Sunlight is so-called electro-magnetic radiation energy of many different wavelengths emitted by the sun; it travels through space at the enormous speed of 186,000 miles per second. Such energy provides us with the heat and light we need to live, as well as delivering damaging ultraviolet (UV) rays. The way in which this radiation affects us depends on its wave-length, which determines how it is absorbed by molecules in different tissues. These tissues include those in the eye that are responsible for vision and those in the skin, which are both susceptible to UV injury. In addition, there are a host of other solar rays, such as cosmic rays, gamma rays, X-rays and radio-frequency radiation, but these are present in too small quantities at the surface of the Earth or of too low an energy to affect the health of our skin.

The solar radiation, its physical characteristics and spectral distribution.

The solar radiation is an integral corpuscular flow (consisting of protons, alfa-elements, electrons, neutrons, neutrinos) and electromagnetic (photon) radiation.

Electromagnetic portion of the solar radiation

(according to R.F.Donnelly, O.R.White, 1980)


Wave lenght l, nanometers

Frequency band

> 100 000

Far-infrared region

100 000 – 10 000

Infrared region

10 000 – 760

Visible (optical) region

760 – 400

Ultraviolet region

400 – 120

Terminal ultraviolet region

120 – 10

Soft X-rays

10 – 0,1

High-energy (gamma) rays

< 0.1


The solar ultraviolet radiation wave lenght less then 290 nm is completely absorbed by oxygen and ozone of the upper atmosphere. Atmospheric pollution by factory waste helps the ozone layer destruction resulting in appearance of “ozone holes”. The shortest and the most harmful UV waves reach the earth surface through these “ozone holes”.

Artificial UVR sources:

·        direct mercury-quartz lamps (MQL), mercury-arc lamps (MAL) generate UVR wave lengths of 240 – 380 nm;

·        erythemal lamps (LE-15, LЕ-30, LЕ-30) – wave lengths of 285-380 nm;

·        bactericidal lamps (LB-30) – wave lengths of 240-380 nm.

The solar and artificial UVR band consists of three regions:

-         region А – long-wave ultraviolet radiation: l = 315-400 nm;

-         region В – middle-wave ultraviolet radiation: l = 280-315 nm;

-         region С – short-wave ultraviolet radiation: l = 10-280 nm.


Spectral distribution and the main characteristics of the ultraviolet radiation are shown in figure 2.1.



Fig. 2.1. Spectral distribution and the main characteristics

of the ultraviolet radiation (UVR)

Biological effects of the ultraviolet radiation may be biogenic (general-stimulatory, vitamin D formation, chromogenic) and non-biogenic (bactericidal, carcinogenic, etc.).

1. General-stimulatory (erythemal) effect of the ultraviolet radiation is typical for the wave length of 250-320 nm, reaching the maximum at 250 and 297 nm (double peak) and the minimum at 280 nm. This effect results in the photolysis of skin proteins (the UV rays may penetrate the skin as deep as 3-4 mm). The following toxic products of photolysis are generated during this process: histamine, choline, adenosine, pyrimidine etc. These substances are absorbed by blood, they can stimulate metabolism, reticuloendothelial system (RES), marrow, rise the levels of haemoglobin, erythrocytes and leucocytes, increase enzyme activity and liver function, stimulate the activity of the nervous system etc.

         The UVR general-stimulatory effect is emphasized by its erythemal effect, which consists in reflex dilation of capillary vessels, particularly when exposed to the intensive infrared radiation. The erythemal effect may result in the skin burn if exposed to the extensive radiation.

2. Vitamin D forming (аntirachitic) effect of the UVR is typical for the 315-207 nm wave length (region B), reaching the maximum at 280-297 nm. This effect consists in the decomposition of calciferols: ergosterin (7,8-dehydrochplecterol) of the skin fat (in sebaceous glands) turns into the vitamines D2 (ergocholecalciferol), D3 (cholecalciferol), and the provitamin 2,2-dehydroergosterin – into the vitamin D4 under the UVR influence due to the decomposition of the benzene ring.

3. Chromogenic(tanning) effect of the UVR is typical for regions A, B with wave lenght of 280-340 nm, reaching the maximum at 320-330 nm and 240-260 nm. Transformation of tyrosine (amino acid), dioxyphenilalanine and the products of adrenaline decay helps to generate the black pigment melanin under the influence of the UVR and the enzyme tyrosinase. This pigment protects the skin and the whole body from the ultraviolet, optical and infrared radiation surplus.

4. Bactericidal(non-biogenic) effect of the UVR is typical for regions C and B with wave lenght from 300 to 180 nm, reaching maximum at 254 nm (according to some other sources – 253.7-267.5 nm). First, the irritation of bacteria under the influence of the UVR activates their metabolism, then a dose increase provokes the bacteriostatic effect and further - photodecomposition, protein denaturation and microorganisms death.

5.Photo-ophthalmic effect of the UVR (the inflammation of the eye mucous membrane) may be observed high in the mountains (“snow disease” among the alpinists), and also among the electric welders and physiotherapists that don’t follow the security rules during the work with the artificial UVR sources.

6. Cancerogenic effect of the UVR is more evident in hot tropical climate conditions and during an exposure to high levels and long-term action of the UVR technical sources (electric welding etc.).

Measuring methods of the ultraviolet radiation intensity

1. An integral (total) flow of the solar radiation is measured by pyranometer (e.g. Yanishevskiy’s pyranometer). The measure units are . The solar constant is 2  at the upper atmosphere and 1  near the earth surface.

2. Biological method – an erythemal dose determination using the Gorbachov’s biodosimeter (fig. 2.2). A minimal erythemal dose (MED) or biodose is the shortest exposure time to the UVR (minutes), which causes the barely perceptible reddening (erythema) on non-tanned skin 15-20 hours after the exposure (for children - 1-3 hours).

Gorbachov’s biodosimeter is 6-window (1.5×1.0 сm) plane-table with the sliding cover, that may close all or some of the windows. This device (biodosimeter) is fixed on the non-tanned skin (the internal surface of the forearm) to determine the biodose. It is useful to mark the window numbers and locations on the skin. After warming up of the lamp (10-15 minutes), a student is exposed to an artificial source of the UVR at the distance of 0.5 m. Then the window #1 is opened, and after that we open a new window every minute. This way, the window #1 is irradiated for 6 minutes, #2 – 5 minutes, #3 – 4 minutes, #4 – 3 minutes, #5 – 2 minutes, #6 – 1 minute. The exposure time and distance may be different depending on a power of the UVR source and other conditions.

The skin is checked for the reddening 18-20 hours after. An erythemal dose is the exposure time of a window with the smallest erythema.

A physiological dose is 1/2 - 1/4, and a preventive dose is 1/8 of erythemal dose.

A preventive dose for the exposure distance, required for the patient can be calculated using the following formula:

where В is a distance from the lamp to the patient in meters;

С – a standard distance for the determination of a preventive dose in meters, (0.5 m);

А – an erythemal dose at a standard exposure distance in minutes.


Comment: As it’s above mentioned, students will only perform the first phase of the biological method measuring during this lesson. They will irradiate the forearm skin of each other using the Gorbachov’s biodosimeter and indicate numbers of windows on the skin. Students will be able to determine the erythemal dose after 18-20 hours. Then they should write it down in the protocol and prepare the calculations of the physiological and preventive doses for themselves for the next lesson.



Fig. 2.2.Gorbachov’s biodosimeter.


3. Photochemical (Oxalic Acid) method was elaborated by Z.N. Kylichkova. It is based on the oxalic acid decomposition being in proportion with the intensity and duration of the UV irradiation in the presence of nitrate uranil.

Measuring result is the mass (in milligrams) of the decomposed oxalic acid per 1 cm2 of the solution surface. An erythemal dose is 3.7 – 4.1 mg/cm2 of the decomposed oxalic acid, a physiological dose is 1 mg/cm2, a preventive dose is 0.5 mg/cm2.

Intensity of the ultraviolet radiation can be determined using this method as the mass (in milligrams) of the decomposed oxalic acid per 1 cm2 of the solution surface per certain amount of time (day, hour).

Reagents: 0.1 n. oxalic acid solution (6.3 g per liter of distilled water); effecting 0.1 n. solution of potassium permanganate (3.16 g КМnО4 per liter of distilled water): effecting 0,1 n. solution of the oxalic acid and nitrate uranil (6.3 g of oxalic acid and 5.02 g of nitrate uranil per liter of distilled water); 6 % solution of sulphuric acid (60 ml of concentrated acid per liter of distilled water).

Order of testing: 

1.     The titer of 0,1 n. solution of potassium permanganate КМnО4 by 0.1 n. solution of the oxalid acid (Т) has to be determined. For this the following should be done: 25 ml of H2SO4  and 25 ml of 0.1 н. solution of the oxalic acid are poured into the volumetric flask, then it is warmed up to 700C on a bain-marie, and titrated by 0.1 n. solution of KМnО4 from a burette until the appearance of the minimally perceptible pink color, that remains visible for 1 minute. The titer is calculated by dividing the volume of the oxalic acid by the volume of the KМnО4 solution, used in the procedure.

2.     An initial volume of КМnО4 solution on effecting solution of oxalic acid with uranil (V1), which will be exposed to the UVR is determined. For this, the solution of pure oxalic acid is replaced by 25 ml of the effecting solution of oxalic acid with nitrate uranil. The titration process is similar.

3.     This solution is exposed in a desired place to determine the UVR intensity there. 25 ml of the effecting solution of oxalic acid with nitrate uranil is poured into a quartz test-tube. This test-tube is overshadowed by black paper with light-window of a certain size.

A closed test-tube is exposed to the sun for a day (to determine the intensity of the Sun or the sky UVR) or to an artificial source of the UVR for an hour (LE-30 lamp, MQ etc). The test-tube is kept in a light-tight case after this exposure.

Comment: Student are provided with pre-made solution to speed up the work.

4.     The volume of КМnО4 solution by solution of oxalic acid with nitrate uranil after an exposure (V2) is determined similarly. The difference between an initial volume of КМnО4 solution and a volume of oxalic acid solution after an exposure to the UVR is the volume of decomposed oxalic acid.

         Intensity of the UVR is determined as the mass (in mg) of the decomposed oxalic acid per 1 cm2 of the surface of solution during the exposure time(hour).

         Intensity of the UVR may be calculated by this formula:

Х = ,


Т – a titer 0.1 n. solution of КМnО4 determined by oxalic acid;

V1 and V2 – volumes of КМnО4, used for titration of oxalic acid with nitrate uranil, before and after an exposure of the UVR, in ml;

6.3 (mg) – the mass of oxalic acid per 1 ml of 0.1 n. solution;

S – a light-window area of quartz test-tube, cm2;

t– the time of a test-tube exposure to the source of the UVR, in hours (to the sun) or minutes (to the artificial source of the UVR).

Comment. The result of the UVR measuring is determined as a mass (in mg) of decomposed oxalic acid per 1 cm2 per minute (from artificial source) or per hour (from the sun).

Conclusion (example).The intensity of the solar UVR, determined by this method is 1.3  of decomposed oxalic acid. This is 0.3 of an erythemal dose. A man needs to receive at least 1/8 of an erythemal dose every day, for this he is required to spend 24 minutes each day outdoors.

4. Physical (photoelectrical) method measures the intensity of the UVR with the ultravioletmeter (short form is uphymeter). Uphymeter is a device containing the magnium (for length range of 220-290 nm) or stibium-caesium (290-340 nm) photoelement. Results of the measuring are represented in mW/cm2 or mcW/cm2.

Due to the erythemal effect being different at various wave length, and being maximal one when l=297 nm, a special unit – microer is introduced. 1 mcer =1 mcW/cm2 when l= 297 nm. The results in mcW/cm2 have to be multiplied by the relative biological effectiveness (RBE) (tabl.1) if the wave length is different.

E.g., the intensity of the UVR, measured by an uphymeter, is 6 mcW/cm2, of which 4 mcW/cm2 at l=297 nm, and 2 mcW/sm2 at l=310 nm. Radiation dose is: 4´1+2´0,03=4,06 mcer. It has been determined, that 1 MЕD=700-1000 mcer; and 1 preventive dose – 100 mcer.

Table 1

Relative biological effectiveness of the UVR different bands


Wave lenght, nm








Relative biological effectiveness








Similarly to the above mentioned, the bactericidal effect is maximal at the wavelength of 254 nm and decreases if the wave lenght is different, so microbact has been introduced.

1 microbact = 1 mcW/cm2 at l=254 nm. A result in mcW/cm2 is to be multiplied by the relative bactericidal effectiveness (RBcE) coefficient (tabl. 2) if the wave lenght is different from 254 nm.

Table 2


Relative bactericidal effectiveness

Wave lenght, nm








Relative bactericidal effectiveness









There are several types of uphymeter. The instructions on using the automatic UVR dosimeter ДАУ-81 (DAU-81) for measuring the intensity of the UVR and radiation dose are given below.

A dosimeter measures an energy (band to 500 W/m2) and dose (band from 10 J/m2 to 15 MJ/m2) of radiation at the exposure angles between +80° and - 80° from the artificial sources: bacteridcidal diapason UVR-DB from 0.22 to 0.28 mcm (region C); lamps LUV-40, LUV-80 with band from 0.32 to 0.40 mcm (optical region).

A dosimeter ДАУ-81 (DAU-81) consists of a measuring block and converters – primary (UV-C) with F-29 photoelement for wave length 0.22 – 0.28 nm (region C); primary (UV-A) with F-26 photoelement and UV and C2C23 color filters for wave length 0.32 – 0.40 mcm (region A); primary (FAR) with F-25 photoelement and C3C25 and ZC4 color filters for wave length 0.38 – 0.71mcm (optical region).

Dosimeter setup. Connect the primary converter for the selected region (C, A or optical region) to the measuring block and a cable of radiation source (UV lamp) to a control system.

Plug the device into the electrical supply network. Press the “Power” button. The device is ready when the pointer is not at 0 immediately after that.

Order of testing. Press “Power” and switch on the dosimeter.

Press the radiation wave band of energetic illumination switch button (“10”) (the primary converter is closed), after that press the “Уст. 0” (Set 0) button to set the microampermeter pointer to zero.

Press the “500” button. Take the deck off the primary converter. Check the data of the ampermeter. Select a more sensitive mode if the pointer shows less than 1/5 of the scale.

Set necessary dose of irradiation according to the sensor.

Press the “Reset” button. The counter has to show zero.

A chime will make a sound and the radiation source (UV lamp) will be switched off when the necessary dose has been reached.

Write down the data, and press “Reset”. The counter has to show zero.

Dosimeter is ready again after a necessary dose of radiation is set according to the sensor.

2.5. Calculation methods of determination of the UV radiation intensity.

2.5.1. The following formula is used for the calculation of erythemal flow from a movable source of the UVR

source of radiation  = 5.4 × S × H/t,


is the general (integral) flow of irradiation device, ;

5.4 – safety factor;

S – area of the room, m2;

t – the duration of the irradiation source work, min;

H – dose of the preventive UV irradiation, .

Values of H:  - if 1 MЕD = 800 mcer (mcW/cm2 ) = 5000 ;

- if1/2 MЕD = 400 mcer (mcW/cm2 )=2500 ;

- if1/4 MЕD = 200 mcer (mcW/cm2 ) = 1250 ;

- if  1/8 MЕD = 100 mcer (mcW/cm2 ) = 625 .

Comment: The calculation of the preventive UVR dose during the exposure to the sun or the open air with the tables is shown in the topic #3 - “Usage of the UV radiation for disease prevention and air sanation”.


When these rays penetrate the Earth's atmosphere, they are modified in various ways. For example, visible light is scattered by atmospheric oxygen and nitrogen molecules in such a way that it makes the sky look blue; in addition, some of the overall radiation energy is absorbed and some reflected back into space by these molecules as well as by atmospheric water vapour, dust particles and other constituents. The result is that only about two-thirds of the solar energy arriving at the surface of the atmosphere pene-trates to ground level, and is made up of about 5 per cent UV, 40 per cent visible and 55 per cent infrared radiation.


Wavelength (nanometres, nm)

Relevance to life on earth

Cosmic rays


Dangerous and potentially cancer-producing, but penetrate to Earth only in insignificant amounts

Gamma rays


Dangerous and potentially cancer-producing, but penetrate to Earth only in insignificant amounts



Dangerous and potentially cancer-producing, but penetrate to Earth only in insignificant amounts; also used artificially in medicine

Ultraviolet (UV)


Causes short- and long- radiation term damage to exposed living matter, particularly, in humans, sunburn, photoageing and cancer of the skin

Visible light


Allows us to see; enables plants to create food molecules; drives human biorhythms; lifts human mood

Infrared radiation


Warms our bodies



Harmless and of no known radiation significant effect; used artificially for tele- communications

Why sunlight is important

The energy from sunlight has been essential for the evolution of life on Earth. It has provided visible light for photosynthesis, the process by which plants use such energy to grow and eventually provide food for other creatures via the food chain. In addition, its infrared rays have given us the warmth we need to live, while visible light is the part of the spectrum that our eyes need to see, and the part that drives our biological, so-called circadian, rhythms. Our mood and sense of well-being may also be affected by visible light; deprivation of bright light can cause a type of winter depression known as seasonal affective disorder (SAD).

Very small amounts of UV radiation also promote the synthesis of vitamin D in the skin, which strengthens bones and thereby prevents rickets. However, vitamin D also comes in our diet - for example, from fish oils, some meats eggs and dairy products which usually provide all we need. Overall, it therefore seems that the UV radiation part of the spectrum may not be of any value to us at all, but instead is just responsible for most of the harmful effects associated with sun exposure, such as skin sunburn, photoageing and cancer. However, UV radiation is also sometimes used by doctors to treat skin conditions if nothing else is effective, although some damage to the normal skin still occurs during that therapy.

UV radiation

The UV radiation component of sunlight is small but biologically important, consisting of the wave-lengths between 100 and 400 nanometres (nm). These are then further subdivided into three categories:

  • UVC: 100-290 nm

  • UVB: 290-320 nm

  • UVA: 320-400 nm.

UVC is completely absorbed by ozone in the atmosphere and does not penetrate to ground level, so the solar UV radiation that reaches us consists only of UVB (up to about five per cent) and UVA (95 per cent or more); these percentages are, however, approximate and the relative amounts vary considerably with the time of day and year, latitude and other factors. Although UVB accounts for only a small proportion of the total solar UV radiation, it is nevertheless extremely important because these are the wavelengths that are mainly responsible for causing sunburn, photoageing and cancer of the skin. This is because they are many times more effective than UVA in causing harmful changes to the genetic material of living cells, namely DNA. As a result, even though UVA comprises about 95 per cent of the total solar UV radiation around midday in summer, it is responsible for only about 10 to 20 per cent of the harmful effects of sun exposure. There is clear evidence, however, that regularly exposing your skin to the high-dose UVA from most sunbeds causes damage similar to that resulting from sunlight, although sunbeds often emit a great deal of UVB as well. UVA also plays an important role in the development of a whole host of abnormal skin rashes caused by the sun.

Other sources of UV radiation

By far the most important source of UV radiation on Earth is the sun, although the radiation is also emitted artificially by many fluorescent and other lamps, and also by arc welding equipment, and may be an important source of exposure for people who work with them. Special UV radiation lamps are also designed for careful use under medical supervision in skin conditions such as psoriasis and eczema. Many people are further exposed in their workplace or at home to very-low-intensity UV radiation from fluorescent lights. As a result of the minimal UV output involved, however, these are not generally believed to cause measurable skin damage. However, tungsten halogen spot lamps are potentially dangerous if used continually, as they can cause sunburn after minutes to an hour or so of exposure and probably have the potential also to cause skin photoageing and perhaps cancer after many years of constant use.

HOW UV radiation behaves

  • UVC (100 to 290 nm) is completely filtered by the ozone layer and does not reach the Earth's surface.

  • UVB (290 to 320 nm) makes up about five per cent of the total solar UV radiation around midday in summer, but is responsible for 80 to 90 per cent of sunburn, photoageing and cancer.

  • UVA (320 to 400 nm) makes up about 95 per cent of the total solar UV radiation around midday in summer, but accounts for just 10 to 20 per cent of UV-related skin damage; however, it plays an important role in the development of abnormal skin reactions to the sun, the most common of which is polymorphic light eruption, commonly known as prickly heat.

How UV radiation levels vary

The factor that mainly influences the intensity of terrestrial UV radiation is the height of the sun in the sky, which depends on the time of day, season and latitude, whereas altitude, cloud cover, terrain and the amount of sky visible are also modifying factors of less importance.

Time of day

The highest levels of UV radiation in the UK are received in summer within the four hours encompassing the solar zenith (when the sun is at its highest point in the sky), namely between 11:00 and 15:00. At this time, the angle of the sun relative to the Earth's surface is such that sunlight has the shortest distance to travel through the atmosphere and the least opportunity to be absorbed or deflected in transit. As a result, about one-third of the total daily UV radiation is received between 12:00 and 14:00, and three-quarters between 10:00 and 16:00.

The higher the sun is in the sky, the shorter the distance sunlight has to travel through the atmosphere and the lower the likelihood of the radiation being absorbed or deflected.

The levels of UVB in particular vary significantly during the day, being much more susceptible to the atmosphere's effects than those of UVA and visible light; thus, UVB intensity increases and then decreases by many times between the hours of 10:00 and 16:00 in summer. In practical terms, there-fore, this means that the risk of sunburn is greatest around 13:00 in this country, namely when the sun is at its highest, although you still need to keep skin exposure to a minimum between around 11:00 and 15:00 in the summer as radiation levels are persistently high during this period.

Changes in UVA and UVB levels ON A TYPICAL


UVA (%)

UVB (%)

UVC (%)





*Relative to intensity of UVA and UVB, respectively, at the solar zenith (13:00).0.0001Dangerous and potentially cancer-producing, but penetrate to Earth only in insignificant amounts

An easy rule of thumb is that, if your shadow is shorter than your height, you shouldn't be exposed to the sun unprotected

An easy rule of thumb is that, if your shadow is shorter than your height, you shouldn't be exposed to the sun unprotected. Early in the morning and later in the day, however, shadows are longer and there is much less harm from sunlight.


Seasonal variations in UV radiation intensity, particularly of UVB, are most pronounced in temperate climates such as in northern Europe, including the UK. In these regions UVB can vary in strength by up to 25-fold between winter and summer. UVA intensity is, however, more constant, being less susceptible to reflection, scattering and consequent weakening during a longer or shorter passage through the atmosphere.On the other hand, nearer the equator, UV radiation levels vary much less, being high all year round, because the sun is always relatively high in the sky in the middle of the day, regardless of the time of year.

The further you move from the equator, the greater the seasonal variation in UV radiation intensity. In other words, the shorter the distance that UV radiation has to travel through the atmosphere, the less opportunity it has to be absorbed or scattered in transit.

Summer solstice (Northern Hemisphere): UV radiation has the shortest distance to travel through the atmosphere.

Vernal/autumnal equinox.

Winter solstice (Northern Hemisphere): UV radiation has the greatest distance to travel through the atmosphere

Geographical latitude

The further you are from the tropics, the less UV radiation there is: the average annual exposure of a person living in Hawaii (20 degrees N) is approximately four times that of someone living in northern Europe (50 degrees N). This again is caused by the increased distance the UV radiation has to travel through the Earth's atmosphere at higher latitudes.

UV intensity increases with altitude because of the reduced distance the radiation must travel through the atmosphere.


As a general rule, for every 300 metres (around 1,000 feet) of increase in altitude, the ability of UV radiation to cause sunburn increases by about four per cent; this is because it passes a shorter distance through the atmosphere to reach high-altitude regions.

Clouds only moderately reduce the amount of UV radiation reaching the ground - you can still burn on a cloudy summer's day.

Cloud cover

Clouds usually only moderately reduce the amount of UV radiation reaching the ground, having a proportionately much smaller effect than they do on temperature, so you can still burn easily on a cloudy summer's day, even if it feels cool. This is because the water in clouds absorbs heat much better than UV rays.

Thus, scattered clouds in a blue sky make only a small difference to the levels of UVB, although complete light cloud cover can, on occasion, reduce the likelihood of sunburn by about 50 per cent, and very heavy cloud by as much as 90 per cent.
In other words, it is still possible to burn in summer even when it is cloudy, cool and dull. Pollution has a similar effect to clouds, again reducing the effects of UV radiation just a little.


Wind, unless very warm, has the falsely reassuring effect of reducing your skin temperature so that you feel cool even though UVB levels are unchanged. You can therefore get as badly sunburned in a breeze as you can without one. This is even more likely on a cloudy day when you may be unaware of the sun's strength and more likely to stay out longer.

Window glass

Most glass used for windows and car windscreens blocks UVB but not UVA nor, of course, visible light. This means that, although glass markedly reduces the risk of sunburn, it does not prevent UVA-induced skin rashes and long-term damage

Some surfaces reflect UV radiation well, allowing more of it to reach your skin and increasing your risk of damage

Surface reflection

Some surfaces reflect UV radiation well, allowing more of it to reach your skin and increasing your risk of sunburn. Thus, grass reflects only about three per cent of UVB whereas a dry, white, sandy beach reflects up to about 25 per cent. However, although calm open water reflects no UVB when the sun is high, rippling water and rough seas reflect much more, perhaps up to 20 per cent. This means that you can get sunburned much more quickly on a beach, even under a parasol, or sailing, than in your back garden. This sunburn risk may be increased still further by UV radiation scattering from the sky (see below). Fresh snow also reflects large amounts of UVB, up to 85 per cent, which, together with the altitude and misleading cooling effects of wind and weather, accounts for the often severe sunburn experienced by unwary skiers, even in winter.


The ambient air temperature (for example, 10°C versus 30°C) or the temperature of any water in which you may be swimming, unless you are on a dive at least several feet below the surface, has little influence on UVB radiation intensity.

Ozone is a gas that prevents much noxious UV radiation from reaching the Earth's surface. Ozone is produced mainly at tropical and mid-latitudes in the stratosphere.

Scattering from the sky

UV radiation does not pass smoothly through the Earth's atmosphere, but undergoes many collisions with air molecules on the way, much as snooker balls collide. As a result the rays reach the ground at all angles from the sky. So when you can see lots of sky you are still at risk of burning and other skin damage from UVB, even if well protected from direct sunlight by clouds, trees, buildings or a parasol. Up to two-thirds of the UVB arrives in this way and only about a third to a half in a direct line from the sun. Visible light and heat are much less affected by this process.


Several factors influence the intensity of sunlight and its potential to cause skin sunburn, photoageing and cancer:

  • Time of day: risk greatest between the hours of 11:00 and 15:00 in the UK, when the sun is highest in the sky

  • Time of year: risk greatest during the summer months, when the sun rises higher in the sky

  • Geographical latitude: risk greatest near the equator, where the sun always rises high in the sky

  • Cloud cover: risk greatest on a cloudless day, although light cloud only mildly reduces this risk; even heavy cloud removes only 50 to 90 per cent of the radiation

  • Reflection: risk greatest near UV-reflecting surfaces, including sand, snow and rippling water

  • Wind and water: risk not affected by the cooling effect of these

  • Amount of sky visible: risk greatest when lots of sky can be seen; up to two-thirds of UVB radiation arrives indirectly at all angles from the atmosphere (scattering) rather than just direct from the sun, so the risk is reduced by only as little as a third if the sun is directly obscured but wide expanses of sky are still visible


Ozone is a gas that prevents much noxious UV radiation from reaching the Earth’s surface. Ozone is produced mainly at tropical and mid-latitudes in the stratosphere.

Ozone depletion and skin cancer

Ozone is a gas created from oxygen in the upper atmosphere by solar UVC radiation; the ozone then absorbs more UVC and some UVB, which turns it back to oxygen again. At present, there is a balance between the production and destruction of ozone, the absorption of all UVC and some UVB in the process preventing much noxious radiation from reaching the Earth. If, on the other hand, all this absorbed radiation did reach us, vast numbers of vulnerable single-celled organ-isms that are part of food chains, such as plankton in the oceans, would very probably die and possibly eventually end all life. While this was threatening, however, we would face increased risks of sunburn, photoageing and cancer, although we could significantly reduce these by taking more care outside.

It is now well known that certain chemicals and gases, predominantly synthetic chlorine and fluorine compounds used as aerosol propellants and coolants in fridges, can alter this ozone balance if they escape into the atmosphere and inactivate the ozone. In 1974, when scientists first saw that this was beginning to happen, they also warned about the resultant potential for an increase in UV radiation intensity at the Earth's surface. Now ozone 'holes', areas of relative depletion, have repeatedly been recorded by scientists from the British Antarctic Survey during the South Polar spring; the problem is more severe in this region because of the extreme cold which intensifies the process of inactiv-ation. For the moment, however, ozone loss elsewhere in the world and at other times of year, when UV radiation intensity is high enough to matter, is much less. Nevertheless, there is considerable concern that the phenomenon may become much more widespread if measures are not rapidly taken to reduce the responsible pollution on a world-wide scale. Fortunately, however, major steps in this direction are indeed now under way.

In summary, despite annual periods of ozone depletion in some parts of the world, particularly the Southern Hemisphere, there has not been a great deal of evidence of any corresponding significant increases in terrestrial UVB levels over the past decades. If the antipollution measures referred to above continue to be adopted, no major increases are now likely; if they are ignored, however, the risk of future problems remains extremely high. It is therefore clear that other factors have more to do with the rise in the incidence of human skin cancer over the last 50 years than any increased UVB levels as a result of ozone depletion. Of these, probably the most important is that we now spend much more of our increasing leisure time in the sun, although the greater age of our population and improved diagnostic techniques are also likely to be significant.


  • The ozone layer of the atmosphere filters out the solar UV radiation most harmful to living matter

  • This layer is now being depleted by synthetic chemicals, which can diffuse into the atmosphere

  • International agreement is currently reducing the use of these chemicals

  • UV radiation intensity, not yet significantly elevated in populated areas, may be maintained at normal levels by these measures

  • Other factors are responsible for the present increasing prevalence of sun-induced skin damage, most likely lifestyle changes

Health Effects of Ultraviolet Radiation

The amount of UV-B radiation in natural sunlight is dependent upon the concentration of ozone molecules in the atmosphere. Any reduction in stratospheric ozone concentration will result in increased amounts of UV-B radiation reaching the surface. Even a small increase in UV-B radiation is likely to have important consequences for plant and animal life, and will almost certainly jeopardize human health. The best understood harmful effects of UV-B radiation on human health are basal and squamous cell cancers of the skin and eye damage, including cataracts, which can lead to blindness.

UV-B radiation also contributes to the development of melanoma skin cancer and perturbs the body's immune system in ways that can reduce immunity to infectious agents, although magnitude of the impacts cannot yet be estimated. UV-B radiation may also affect human health indirectly by interfering with the food chain. On a global scale, UV-B radiation may increase the infectious disease burden, cause blindness, and reduce the world's food supply.

The current pattern of ozone depletion will cause the incidence of skin cancer to continue to rise at least until the year 2050 and probably beyond. For each 1% reduction in ozone, the incidence of non-melanoma skin cancer will increase by 2%. This means that a sustained 10% decrease in the average ozone concentration would lead to about 250,000 additional non-melanoma skin cancers each year. Each 1% decrease in ozone concentration is estimated to increase the incidence of cataracts by about 0.5%. Increased UV-B radiation could increase the severity of some infections in human populations. Furthermore, skin pigmentation does not seem to provide much protection against the immunosuppressive effects of UV irradiation in humans. Any lowering of immune defenses is likely to have a devastating impact on human health.

UV rays

Johann W. Ritter

Johann W. Ritter was a German physicist born on December the 16th, 1776 in Samitz bel Haynau Silesia, now Poland. He devoted his efforts to studying electricity and electrochemistry. However his main discovery was the ultraviolet region of the spectrum. In 1801 he conducted experiments with silver chloride and a prism. He projected a beam of sunlight through the prism, which split the beam into the colors of the spectrum. He them put chloride in each color to see the outcome. The red caused a small change while the deep violet darkened the chloride. Ritter placed chloride in the lightless area just beyond the violet and it darkened as it were in a smoky fire. The was evidence of another wave form just barely higher than the violet of visible light. It is now known as ultraviolet or UV light. It wasn't until the twentieth century, however, that any photographic records in either of these spectra were made

Solar Ultraviolet or UV rays make up part of the electromagnetic or photonic spectrum of light and radiant energy. Part of this spectrum is broken down into wavelengths and is measured by nanometers or nm, for short. The electromagnetic spectrum within the wavelength region ranges from the vacuum ultraviolet to the far infrared. We cannot see ultraviolet light and it is shorter in wavelength than visible light. Ultraviolet radiation (UV) comes naturally from the sun. There are also some manmade lamps and tools (welding tools, for instance) that can produce UV radiation. For most of us, however, the sun is the primary source of UV. UV is divided into at least three different categories based on wavelength:

  • UVA wavelengths (320-400 nm) are only slightly affected by ozone levels. Most UVA radiation is able to reach the earth's surface and can contribute to tanning, skin aging, eye damage, and immune suppresion.

  • UVB wavelengths (280-320 nm) are strongly affected by ozone levels. Decreases in stratospheric ozone mean that more UVB radiation can reach the earth's surface, causing sunburns, snow blindness, immune suppression, and a variety of skin problems including skin cancer and premature aging.

  • UVC wavelengths (100-280 nm) are very strongly affected by ozone levels, so that the levels of UVC radiation reaching the earth's surface are relatively small.

The effects of UV radiation on earth's ecosystems are not completely understood. Even isolating the effects of UVA versus UVB is somewhat arbitrary. All UV radiation can be damaging. This knowledge has prompted many manufacturers of sun screen and sunglasses to offer products that protect against both UVA and UVB wavelengths.

While humans can choose various courses of protection, for instance avoiding noon-time sun, plants and animals are not so fortunate. Studies have shown that increased UV radiation can cause significant damage, particularly to small animals and plants. Phytoplankton, fish eggs, and young plants with developing leaves are particularly suspectible to damage from overexposure to UV.

Solar UV radiation levels are highest during the middle of the day. In total, almost half the daytime total UV radiation is received during the few hours around noontime. Clouds, as well as ozone, have a tremendous affect on UV radiation levels. However, cloudy skies generally do not offer significant protection from UV. Thin or scattered clouds can have minor impacts on UV and even, for a short time, increase UV above what it would be on a blue sky day by further scattering the radiation and increasing the levels that reach the surface.

To determine UV ray levels an  instrument capable of measuring these "invisible" rays must be used.


The earth's ozone layer is not as thick as it used to be and more ultraviolet radiation from the sun reaches us. Exposure to ultraviolet radiation, often referred to as "UV rays", can cause skin cancer and other serious health problems.

Fortunately, there are simple guidelines to follow to protect against damage from the sun's harmful rays.

Ultraviolet radiation (UV) is a type of invisible light sent out by the sun and by certain kinds of lamps. By now, most people have heard that exposure to ultraviolet radiation can cause skin cancer. It has also been linked to a number of other health problems, including sunburns, cataracts, premature aging of the skin, and weakening of the immune system.

For centuries, the earth's ozone layer protected people from the sun's harmful rays. However, over time, the release of certain chemicals into the environment has damaged the ozone layer. It is thinner than it used to be, so more ultraviolet radiation is getting through to the earth's surface.


Many countries around the world, including Canada, have recognized this problem and have taken steps to protect the ozone layer from further damage. Efforts have focused mainly on controlling the production and use of chemicals that are known to damage the ozone layer.

When grouped together, these chemicals are called ODCs, which stands for "ozone-depleting chemicals". These kinds of chemicals are mainly used in refrigeration and air-conditioning.

Minimizing Your Risk

There is no quick fix for the ozone layer. Once they get into the environment, ozone-depleting chemicals disintegrate very slowly, so they are likely to be with us for a long time. While governments around the world deal with the source of the problem, we should all take steps to avoid over-exposure to ultraviolet radiation.

These general guidelines will help you protect your family from the sun's harmful rays:

§        Cover up when you are going to spend long periods in the sun. Wear long-sleeved shirts, long pants, gloves and a brimmed hat or visor. Avoid see-through clothing when possible.

§        Avoid sunbathing for the purpose of tanning, especially between 11 a.m. and 4 p.m. when the sun's rays are strongest.

§        Wear sunglasses that screen out ultraviolet radiation. Our eyes have no built-in defence against the sun, and damage to the eye from UV rays can lead to cataracts.

§        Use lots of sunscreen lotion, and reapply it every two hours. Look for a sunscreen with a sun protection factor (SPF) of at least 15.

§        Don't think you are safe just because it's cloudy. The sun's harmful rays can get through fog, haze and light cloud cover.


People who work outdoors should avoid prolonged exposure to sunshine because of the damaging effects of ultraviolet (UV) radiation from the sun.


Excessive exposure to the sun's radiation over the years is a factor related to premature skin aging, skin cancer, and cataracts in older people.

The UV levels are highest in spring and summer between 10 a.m. and 4 p.m. At noon on a clear summer day, for example, it can take only 15 minutes to cause a sunburn on unprotected fair skin.

To reduce the exposure of workers to ultraviolet rays while working in direct sunlight when UV levels are high, the following precautions are recommended:

§        Wear a hat.

§        Wear tightly-woven clothing covering as much of the body as is practicable.

§        Apply sunscreen with a Sun Protection Factor (SPF) of 15 or higher on exposed skin. The sunscreen should be effective in filtering both UV-A and UV-B rays; this information is usually printed on the product's packaging.

§        Wear eyeglasses that effectively filter ultraviolet rays. Plastic safety glasses and plastic cosmetic sunglasses have been found to be good UV filters. UV filtering factors appropriate for sunglasses used for different purposes are specified in the CSA Standard Z94.5-95, "Nonprescription Sunglasses."

Children Need Extra Protection

Children and teenagers have thinner skin than adults, so they need extra protection if they are going to be out in the sun for a long time. Sunburn may increase the risk of skin cancer later in life, so it is best to get children used to wearing protective clothing and sunscreen lotion from the start.

At the very least, young children should wear a sunhat, T-shirt and shorts. When you put sunscreen on children, pay special attention to the parts that are most exposed, including their ears, face, neck, shoulders and back, knees and the tops of their feet. Don't use sunscreen on babies. Keep them in the shade instead.

It is important to protect against ultraviolet radiation all year round; not just in the summer. You can continue to enjoy outdoor activities, as long as you take steps to avoid sunburns and over-exposure to the sun's harmful rays.

Government of Canada's Role

Back in 1987, Canada was one of 24 nations to sign the Montreal Protocol on Substances that Deplete the Ozone Layer. This was the first international agreement to limit the use of ozone-depleting chemicals. Since that time, more than 70 countries have signed the Montreal Protocol, which now calls for the total elimination of ODCs by the year 2005.

On the domestic front, Canada has phased out the production of all ozone-depleting chemicals, and has taken steps to control the use of ODCs through regulations that are part of the Canadian Environmental Protection Act (CEPA).


A sun-tan may look good but is not healthy. Sun exposure to fair skin is important in skin aging and skin malignancy. The wavelengths of the solar radiation involved are in the ultraviolet (UV) spectrum - from 200-400 nm. The  increased incidence of cutaneous malignancy from sun exposure and increased UV radiation (UVR) caused by thinning of the stratospheric ozone  is now a major health concern. Ozone is one of the natural sunscreens the upper atmosphere and used to be a more effective filter against solar ultra-violet radiation.  UV exposure causes sunburn, skin aging, photodermatoses and skin cancer. Ultaviolet light is divided into three bands; A, B & C. UVA and UVB are both responsible for photoageing.

Ultraviolet sub-bands:

UVA : at wavelengths of 320-400 nm accounts for  90% of UVR reaching the Earth's surface.

UVB : 290-320 nm  is 10% of UVR reaching the earth surface and  is largely responsible for skin cancer.  UV-B is absorbed in the upper stratosphere (about

25 miles above the earth) at the level of the ozone layer.uVB is 1000 times more potent in causing sunburn (erythema) than UVA.

UVC : 200-290 nm  is absorbed in the upper atmosphere, but would cause severe cellular damage if it reached living organisms.

New and wether information services are now providing infomation about UV levels. The UV Index  can warn people about the local and immediate risk of UV exposure. 

UV effects on Gene Expression

UV light changes the behavior of skin cells by changing the expression of genes and/or damaging DNA. UV radiation causes cyclobutane phyrimidine dimers, 6-4 photo products and single strand breaks. UV increases synthesis of transcription factor proteins that enter the nucleus, bind to genes and increases production of the protein transcribed by the gene.  Protective substances in cells such as p53 can repair DNA damage and stop cells from proliferating. Imperfect repair leaves permanent mutations with changes in the growth characteristics of the skin and rick of cancer.

Protective Measures

§        Avoid  sunburns

§        Avoid tanning parlors

§        Use  protective clothing and sunscreens

§        Checkout any supicious skin lesion

Sunscreens are no substitute for avoidance of mid-day sunlight and protective clothing. Recent studies suggest that people are using sunscreens more frequently and exposing themselves more often to sun,  increasing the total dose of UVR  they receive.

Sunscreens can be divided into 2 main types :

Physical:  These are opaque pastes and creams that reflect or scatter incident UVR. Examples are zinc oxide, titanium dioxide and magnesium silicate. They protect against both the UVB and UVA. The white paste, zinc oxide is the most effective sunblock. A transparent, micronized form of zinc oxide has been marketed as Z-Cote and is be incorporated into a number of other skin products.

Chemical: These chemicals act by absorbing UVB: para-aminobenzoic acid (PABA), PABA esters, salicylates, cinnamates, anthranilates and the benzophenones. Benzophenone compounds  absorb UVB and  wavelengths from 250-365 nm,  However, it is less effective than PABA in the UVB spectrum. Cinnamates can also absorb UVA. Sunscreen   products often contain more than more than one active ingredient.

Examples of commonly used preparations are :

Sunsense : Titanium dioxide Co 3%, Oxybenzone 5%, Ethylhexyl-p-methoxycinnamate 7.5%, Butylmethoxy-dibenzoylmethane 1.5 %

(ii) Coppertone : Ethylhexyl p-methoxylcinnamate, 2-ethylhexyl salicylate,   Octocrylene, Oxybenzone

A Sun Protection Factor (SPF *) >15 is required; more than 15 times the sun exposure is required to produce the same reddening of skin by comparison with unprotected skin. The greater the SPF, the greater the protection. Sunscreen agents such as PABA esters are potential sensitizers, causing allergic contact dermatitis.

Protecting Yourself

Being outdoors in the sun is good for you. Just remember to take a few simple precautions to protect yourself from the sun’s harmful rays throughout the year.

In the late winter and early spring, fresh white snow can increase the amount of UV radiation you receive by up to 85 percent. Protect yourself on the ski slopes or on the trails by wearing sunscreen on your face and sunglasses to protect your eyes.

In the summer time, considering doing outdoor activities such as swimming before 11 a.m. or after 4 p.m. Remember, too, that water and sand reflect UV radiation. Try to spend less time in the sun by finding shade. When you are outdoors, wear clothes that cover your skin such as hats, shoes, long pants and long-sleeved shirts. Protect your eyes with sunglasses that are UV rated. Wear a lot of sunscreen on skin that is not covered. Your sunscreen should block both UV-B and UV-A and have a SPF (sun protection factor) of at least 15 or more. Be sure to reapply it every two hours or after swimming or exercising.

In the spring and fall, UV radiation from the sun can be very strong especially in the spring when ozone depletion is of concern. When outdoors, wear protective clothing, sunglasses, and a hat. Put on sunscreen to protect any exposed skin. Burns and skin damage can occur quickly and stay with you for life.

When should you start practicing these protective behaviors? Right away when you are in the sun. We now know that it takes very little time for the UV rays to damage your DNA, increase your risk to skin cancers, weaken your immune system and damage your eyes. By the time you see it, damage has been done. So start practicing as soon as you are in the sun!

UV Index Sun Protection Messages

UV Index


Sun Protection Actions

0 - 2




  Minimal sun protection required for normal activity

  Wear sunglasses on bright days. If outside for more than one hour, cover up and use sunscreen

  Reflection off snow can nearly double UV strength. Wear sunglasses and apply sunscreen

3 - 5



  Take precautions – cover up, wear a hat, sunglasses and sunscreen - especially if you will be outside for 30 minutes or more

  Look for shade near midday when the sun is strongest

6 – 7




  Protection required – UV damages the skin and can cause sunburn

  Reduce time in the sun between 11 a.m. and 4 p.m. and take full precautions – seek shade, cover up, wear a hat, sunglasses and sunscreen

8 - 10


Very High


  Extra precautions required – unprotected skin will be damaged and can burn quickly

  Avoid the sun between 11 a.m. and 4 p.m. and take full precautions – seek shade, cover up, wear a hat, sunglasses and sunscreen

11 +


  Values of 11 or more are very rare in Canada . However, the UV Index can reach 14 or more in the tropics and southern U.S.

  Take full precautions. Unprotected skin will be damaged and can burn in minutes. Avoid the sun between 11 a.m. and 4 p.m. , cover up, wear a hat, sunglasses and sunscreen

  White sand and other bright surfaces reflect UV and increase UV exposure


Sun Protection Tips

  The amount of UV you receive depends on both the strength of the sun's rays (measured by the UV Index) and the amount of time you spend in the sun. Reduce your time in the sun – seek shade, particularly between 11:00 a.m. and 4:00 p.m. from April to September.

  Cover up, wear a broad-brimmed hat, a shirt with long sleeves and wrap-around sunglasses or ones with side shields

  Use sunscreen – with a sun protection factor (SPF) of 15 or higher, with both UVA and UVB protection. Apply generously before going outside, and reapply often, especially after swimming or exercise

  Listen for Environment Canada’s UV Index – it’s included in your local weather forecast whenever it is forecast to reach 3 (moderate) or more that day.

Creating a Safe Environment

Education about sun safety

Education is a key strategy in bringing greater awareness of the changes to the ozone layer, of the dangers of over exposure to UV radiation and in promoting sun sensible behavior.

School children spend much time outside when the sun is strong especially during lunch time, recess and sport activities. As part of public health and safety, helping young people protect themselves from the sun now will go a long way to preventing serious health problems later in life.

It is during our younger years that we receive most of our lifetime's exposure to ultraviolet radiation from the sun. Damage in the form of a sunburn stays with us for life and can be dangerous later in life. Parents, teachers, and schools can participate by educating children about sun safety, UV radiation and the ozone layer and by protecting children from over exposure. Here are some simple ideas to follow.

Limiting time in the sun

Reducing students exposure can be done by planning outside school activities outside the hours from 11 a.m. to after 4 p.m. If children are outside during this time period, it should be school policy that children wear a hat, sun glasses, apply sunscreen and are wearing protective clothing. Before 11 a.m. check the UV Index and ensure children are taking the appropriate protective measures.

Ensuring that there is plenty of shade in the schoolyard will help reduce exposure to the sun at lunchtime. Schools can ensure that there is plenty of temporary shade available for playgrounds, sport days and sport tournaments.

Different kinds of radiation influence on peoples.

Among well-known springs and kinds of natural ray energy, we need say about sun, radioactive and cosmic radiation. All this kinds of ray energy influences on ours organism. However, more importance for man is a sun radiation. Sun and life, - Wright K. L. Timiraysev, - this two-conception person may be, can connect, compare, than, when can analyze our selves and environment.

We can say about influence sun radiation in prophylactics of tuberculosis, catarrh diseases and others. Well-known bactericides relation of sun ultraviolet radiation. Big meaning has sun radiation for hardening organism. Sun radiation usage not only for prevent different diseases, it usage for cure this diseases too.

Progress of sun curing in our country connects with name, V. Z. Snegirov. In 1882 years he first usage sun ray for curing gynecological patients. In 1901 V. N. Tomshevskiy begin studding bactericides relation of sun - light . He shows main role ultraviolet rays in influencing on microorganism.

In connecting with more importance discover of investigators in branch of electrolight techniques appears possibility use piece lightening.

Distributors of piece lightening were Shtane, Zachnovsky, Evalgl, Kozlovsky, Minin and others.




Spectrum of the Sun Radiation.

Spectrum of the Sun Radiation from the sun is photographed using a spectrometer and is analyzed through the use of a spectrograph. The dark lines in the spectrum are called absorption lines, and are caused by the absorption of radiation by elements in the sun’s atmosphere. By studying these absorption lines, scientists are able to identify the elements present in the sun. The prominent line at the red end of the spectrum is one of the hydrogen lines and the lines in the yellow indicate the presence of sodium. 

Sunlight appears yellowish, but it is actually a combination of a rainbow of colors. Scientists use special instruments called spectrographs to separate sunlight out into its different colors. These instruments do the same thing that water molecules in the atmosphere do when the molecules produce a rainbow. Each color corresponds to a different wavelength of light. Red has the longest wavelength of visible light, and violet has the shortest. The range of wavelengths of sunlight and the intensity at each wavelength are called the Sun’s spectrum. The study of the spectra of the Sun and other objects or materials is called spectroscopy.

When sunlight is spread out like a rainbow in the Sun’s spectrum, many dark gaps separate one color from another in the row of colors. These gaps are called absorption lines. Each absorption line is created when sunlight passes through the gases in the Sun’s photosphere. Atoms and ions of each element in the gas absorb light at certain wavelengths, creating dark gaps in the Sun’s spectrum.

The dark absorption lines in the spectra of the Sun and other stars fingerprint the ingredients of these stars. Each chemical element produces a unique set of lines, and the presence of these lines shows that a particular element is present in the stellar photosphere. Darker absorption lines indicate greater absorption and therefore larger amounts of the element.

Absorption lines in the Sun’s spectrum show that hydrogen is by far the most abundant element in the Sun. Other prominent absorption lines are produced by helium, sodium, calcium, and iron. Altogether, 92.1 percent of the atoms in the Sun are hydrogen atoms, 7.8 percent are helium atoms, and the other, heavier elements—sodium, calcium, iron, and other elements—make up only 0.1 percent of the atoms in the Sun. The Sun’s absorption lines are called Fraunhofer lines, named after German physicist Joseph von Fraunhofer, who cataloged them in the 1800s. The most common Fraunhofer lines are listed below, by the letter Fraunhofer gave them, the color that they block, and the element that causes them.

The Fraunhofer lines designated A and B actually have nothing to do with the composition of the Sun. They only appear on spectra gathered within Earth’s atmosphere. Earth’s atmosphere absorbs sunlight at the wavelengths of the A and B Fraunhofer lines, creating dark lines on the Sun’s spectrum. A spectrum gathered above Earth’s atmosphere would not have these lines.

    The physiological role of daylight inside of house (apartments, room) is that daylight renders a favorable influence on mental condition of the person, especially ill. One the rational lighting has positively effect on a functional state of a cortex of the brain, improves the function of other analyzers. Under the influence of light the metabolism in an organism of the person strengthens, the synthesis of vitamin D is carried out; the processes of a hemopoiesis, the work of closed glands are improved. The mode of lighting plays an essential role in a regulation of biological rhythms. In conditions of intensive lighting the growth and development of the human’s organism is improved.

    The light intensity of a job’s (work’s) place has large significance for preventive maintenance of violation of vision. The no rational lighting promotes development of near-sightedness. One to bad or incorrect daylight the mental serviceability is reduced, the fatigue of an organism occurs fast, the coordination of movements is worsened. Besides the daylight is renders a thermal, physiological and bacteriological effect. There fore residential, industrial and public buildings should be provided with daylight.

       Owing to a large physiological significance of a visible part of the solar spectrum all locations of preventive establishments which are intended for long stay of patients should have daylight. At a bad daylight (dark time of day, bad weather) the sources of artificial lighting should be used.

       The daylight should be steady, with sufficient intensity, not to render for blinding operation, not to create sharp shades.

      The daylight in rooms depends on a light climate, which develops on general climatic conditions of locality, degree of an air transparency, echoing properties of an environment.

       The orientation of windows has also the relevant significance on also the parties of light defining a insole mode of locations. Depending on orientation of windows  three types of insole mode are distinguished.

Types of insulation mode in room

Insular mode of

Orientation windows on the world sides

Time of insulation


% square of room, which insulation

A heat quantity expense at the solar radiation



the South-East,  the South-West



more 3300


the South,

the East





the North-East the North-West

< 3

< 30

< 2100

         The insular  mode of locations should be taken into account at patient’s wards.

In moderate and southern attitudes hospital wards, the room of day time stay should be oriented on the South or South-East, for maintenance of sufficient illuminant and insulation of a place without an overheating.

To the North-up, North-West, North-East are oriented the dressing rooms, rooms for medical procedures , operational, reemission rooms, that ensures a even steady daylight of these places with an indirect lighting and excludes a superheating of rooms blinding effect of sun rays and appearance of a spangle from medical tools.

The lighting depends on distance between buildings  height and proximity of green plantations. A denseness of buildings in a district quarter and close disposition of houses to each other leads to a considerable loss of a solar radiation, especially in the lower levels.

The essential factor that influences on intensity and duration of daylight of rooms, is the size, form and disposition of windows. The upper edge of windows is necessary to higher as it is possible. The area of windows should correspond  to area of room. Therefore a widespread method of evaluate of a daylight is geometrical, at which one calculate light coefficient (LC), i.e. attitude of a glass area of windows to area of a floor of room. The more size of light factor, the better is lighting. For living rooms LC = 1:6 - 1:8, for hospital wards, the doctors cabinets, educational classes 1:5 - 1:6, for operational, birth wards, observation, dressing rooms, labs 1:3 - 1:4, for extra locations 1:10 - 1:12.

 The best in form are the rectangular windows, and the upper edge of the window should be placed from a ceiling on 20-30 cm., for maximum receipt of light to the depth of rooms.

At contamination of glasses the lighting in room decreases on 50-70  %.

The lighting in room is depend on coloring of a ceiling, floor, walls, furniture in the room. The dark colors swallow a plenty of light rays, therefore coloring of locations and furniture at schools, children's preschool and preventive establishments should be brighten. The white color and light tone are mirrored by sun rays on 70-90 %, yellow color - on 50 %, green - on 50-60 %, blue, violet - on 10-11%, black - on 1 %.

The basic lighting engineering parameter for a normalization of a daylight is coefficient of daylight (CDL).This attitude of lighting indoors to simultaneous lighting  outdoor, expressed in %. For living rooms CDL must be not less than 0,5 %, for hospital wards - not less than 1 %, for school classes - not less than 1,5 %, for operational - not less than 2,5 %.

The angle of incidence of light rays is an angle between a horizontal surface of a table, and line conducted from this surface to the upper edge of the window. The more erectly direction of light rays, i.e. the more angle, the lighting is more. For living rooms the angle of incidence in norm should be not less than 27°.

Coefficient of depth(CD ) of room - this is a attitude of distance from the upper edge of the window to a floor to distance from the window to the opposite wall. The hygienic norm CD is no more 2.


Description of natural illumination of workplaces



Coefficient of daylight (CDL)

not less 0,75 %

Light coefficient (LC)

not less 1/6-1/8

Angle of incidence of light rays

not less 27°

Angle of opening

not less 5°

 Coefficient of depth of room(CD)

no more 2


 The estimation of illumination is made on an illumination level of a horizontal surface on a job place with the help of a luxmeter. An accepting part of the instrument is the photo cell conversing a quantity of light in electrical. A recording part is the sensing galvanometer calibrated in luxs. The obtained result is compared to the established norms.

Appraisal of artificial lighting.

While appreciation of artificial lighting first of all sufficiently of light is measured by directly definition of lighting in lodging. The results are usually compared with well-known hygienic norms. Then one should characterize the light, in particular to indicate whether it is similar to the day light, whether is even, whether it has blinding effect and so on. For answering these questions we have to indicate the kind of light source, the system of lighting, the type of lighting device (chandelier of direct light, of diffused light, of repulsed light, the height of its location, the order of its location, the force of lamps, properties of protective stuff and its ability to make the brightness less. It is also important to establish the presence of shadows on working surface of table; the contact between brightness of working surface and surroundings. Also one have to find whether light sources have blinding effect at the expense of light repulsing from smooth and polishing surfaces and objects. The aim of creating of hygienic norms for lighting is to make the most favourable conditions for eye work. That provides its great working ability and minimal weariness. The functions of eye lights depend of lighting conditions. In sufficient lighting eye can perform its function without stress; on the contrary in irrational lighting eye gets tired very quickly.

Electric Lighting, illumination by means of any of a number of devices that convert electrical energy into light. The types of electric lighting devices most commonly used are the incandescent lamp, the fluorescent lamp, and the various types of arc and electric-discharge vapor lamps .

Neon Lights at Night Bright neon lights shine throughout the night in Las Vegas, Nevada. Neon lamps are used for art, advertising, and even airplane beacons. They are made by evacuating air from glass tubes, then filling them with neon gas. When the light is “on,” an electric current flows through the gas between two electrodes sealed within the tube. The neon forms a luminous band between the two electrodes. 


Incandescent Lamp In an incandescent lamp, an electric current flows through a thin tungsten wire called a filament. The current heats the filament to about 3000° C (5400° F), which causes it to emit both heat and light. The bulb must be filled with an inert gas to prevent the filament from burning out. For many years incandescent lamps were filled with a mixture of nitrogen and argon. Recently the rare gas krypton has been used because it allows the filament to operate at a higher temperature, which produces a brighter light.

If an electric current is passed through any conductor other than a perfect one, a certain amount of energy is expended that appears as heat in the conductor . Inasmuch as any heated body will give off a certain amount of light at temperatures above 525° C (977° F), a conductor heated above that temperature by an electric current will act as a light source. The incandescent lamp consists of a filament of a material with a high melting point sealed inside a glass bulb from which the air has been evacuated, or which is filled with an inert gas. Filaments with high melting points must be used because the proportion of light energy to heat energy radiated by the filament rises as the temperature increases, and the most efficient light source is obtained at the highest filament temperature. Carbon filaments were employed in the first practical incandescent lamps, but modern lamps are universally made with filaments of fine tungsten wire, which has a melting point of 3410° C (6170° F). The filament must be enclosed in either a vacuum or an inert atmosphere, otherwise the heated filament would react chemically with the surrounding atmosphere. Using an inert gas instead of a vacuum in incandescent lamps has the advantage of slowing evaporation of the filament, thus prolonging the life of the lamp. Most modern incandescent lamps are filled with a mixture of argon or krypton and a small amount of nitrogen.

Radical changes in incandescent lamp design have resulted from substituting compact fused-quartz glass tubes for glass bulbs. These new, stronger-walled bulbs have made tungsten-halogen lamps, a variation of the incandescent lamp, possible. Tungsten-halogen lamps use the regenerative cycle of halogens to return evaporated tungsten particles to the filament, thus extending the life of the bulb. The high temperatures required to take advantage of halogen’s regenerative cycle made this idea impossible until the walls of the bulb could be made stronger by the introduction of quartz. These bulbs are filled with a mixture of argon and halogen (usually bromine) gases along with a small amount of nitrogen.


Components of a Fluorescent Lamp A fluorescent lamp consists of a phosphor-coated tube, starter, and ballast. The tube is filled with an inert gas (argon) plus a small amount of mercury vapor. The starter energizes the two filaments when the lamp is first turned on. The filaments supply electrons to ionize the argon, forming a plasma that conducts electricity. The ballast limits the amount of current that can flow through the tube. The plasma excites the mercury atoms, which then emit red, green, blue, and ultraviolet light. The light strikes the phosphor coating on the inside of the lamp, which converts the ultraviolet light into other colors. Different phosphors produce warmer or cooler colors. 

Electric-discharge lamps depend on the ionization and the resulting electric discharge in vapors or gases at low pressures if an electric current is passed through them . Representative examples of these types of devices are the mercury-vapor arc lamp, which gives an intense blue-green light and is used for photographic and roadway illumination, and the neon lamp, which is employed for decorative sign and display lighting. In newer electric-discharge lamps, other metals are added to mercury and phosphor on the enclosing bulbs to improve color and efficacy. Glasslike, translucent ceramic tubes have led to high-pressure sodium vapor lamps of unprecedented lighting power.

The fluorescent lamp is another type of electric-discharge device used for general-purpose illumination. It is a low-pressure mercury vapor lamp contained in a glass tube, which is coated on the inside with a fluorescent material known as phosphor. The radiation in the arc of the vapor lamp causes the phosphor to become fluorescent. Much of the radiation from the arc is invisible ultraviolet light , but this radiation is changed to visible light if it excites the phosphor. Fluorescent lamps have several important advantages. By choosing the proper type of phosphor, the light from such lamps can be made to approximate the quality of daylight. In addition, the efficiency of the fluorescent lamp is high. A fluorescent tube taking 40 watts of energy produces as much light as a 150-watt incandescent bulb. Because of this illuminating power, fluorescent lamps produce less heat than incandescent bulbs for comparable light production.

One advance in the field of electric lighting is the use of electroluminescence, known commonly as panel lighting. In panel lighting, particles of phosphor are suspended in a thin layer of nonconducting material such as plastic. This layer is sandwiched between two plate conductors, one of which is a translucent substance, such as glass, coated on the inside with a thin film of tin oxide. With the two conductors acting as electrodes , an alternating current is passed through the phosphor, causing it to luminesce. Luminescent panels may serve a variety of purposes—for example, to illuminate clock and radio dials, to outline the risers in staircases, and to provide luminous walls. The use of panel lighting is restricted, however, because the current requirements for large installations are excessive. .

A number of different kinds of electric lamps have been developed for such special purposes as photography and floodlighting. These bulbs are generally shaped to act as reflectors when coated with an aluminum mirror . One such lamp is the photoflood bulb, an incandescent lamp that is operated at a temperature higher than normal to obtain greater light output. The life of these bulbs is limited to 2 or 3 hours, as opposed to that of the ordinary incandescent bulb, which lasts from 750 to 1000 hours. Photoflash bulbs used for high-speed photography produce a single high-intensity flash of light, lasting a few hundredths of a second, by the ignition of a charge of crumpled aluminum foil or fine aluminum wire inside an oxygen-filled glass bulb. The foil is ignited by the heat of a small filament in the bulb. Increasingly popular among photographers is the high-speed gas-discharge stroboscopic lamp known as an electronic flash.

The sources of artificial lighting.

There are two main sources of artificial lighting: incandescent bulbs and luminescent lamp. A bulb is very convenient source of light. Its deficiency is a very small light returning: on 1 Vat of expended electric energy one can receive 10-20 lm. The spectrum of its radiation differs from the spectrum of white daylight. It has less quantity of blue and violet radiation and more red and yellow one. That’s one taking into consideration psycho-physiological side this radiation is pleasant and warm.

Luminescent lamp consists from glass tube. The internal surface of this glass is covered by luminoforum. The tube is full of mercury steam. At the ends it has electrodes. When the lump is switched in the electric net on, the electric current creates between the electrodes. It generates ultraviolet radiation. Under ultraviolet radiation influence luminofor starts to shine. Thus choosing different kinds of luminofor one can made luminiscent lamps with different spectrum of visible radiation: lamps of day light, white light, warm-white light. The spectrum of day light lamp radiation is very clothing by spectrum of natural lighting of lodging, situated on the north. This light helps to get tired less, even if we look at very small subject. To deficiency of lamp one can attribute blue color at surroundings: skin… and so on.

Lighting appliance of bulbs.

There are lighting appliance of direct light, reflected light, half-reflected light, and diffused light. The lighting appliance of direct light directs over 90% of lamp light to the lighting place, providing its high lighting. But at the same time there is a great difference between the lighting and sun lighting places of lodging. Harsh shadows are created sometimes it can blind there person. Usually this kind of lighting appliance is used for lighting of auxiliary lodging and sanitary lodgings. The appliance of reflected light is characterised by the fact, that rays from lamp are directed to the ceiling and upper part to the walls. They are repulsed, and evenly, without shadows, are divided in lodging. Their light is soft and diffused. This kind of lighting appliance creates lighting, which exactly corresponds to hygienic norms. But it is not economic one. Because in this case 50% of light is lost. That’s for lighting of settlements, classrooms, wards more economic lighting appliance is used – appliance of diffused light. In this case a part of rays shine the lodging after coming through milk or mat glass, and part of rays shine the lodging after repulsing from ceiling and walls. Such lighting appliance creates satisfactory conditions of lighting, does not blind and doesn’t create harsh shadows.

Deficiencies of luminiscent lamps (compared with bulbs).

One of the deficiencies of luminiscent lamp is that the skin of people in this light looks very pale or grey. That’s why there lamps are not used in schools, wards and others lodging like these. Becides there are another deficiency. If lighting in case of using luminiscent lamps is power than 750-150 Lk, one can see “twilight effect”. That means lighting is insufficiently even to look at big object. That’s why while using luminiscent lamps, lighting should be not less than 75-150 Lk. Besides while looking at moving or rotating object in luminiscent lighting sometimes “stroboscope effect” can occur. That means creating of numerous contours of objects. When dossals are out of order luminiscent lamps radiate pulse light or create noise.

The spectrum of worm-white lamps is rich on yellow and rose rays. This can make the colour of face more pleasant. But at the same time these lamps decrease eye capacity for work. These lamps are used for lighting of railway station, hall, and cinemas, metro stations.

Advantages of luminiscent lamps compared with bulbs.

       The bulb cannot be used when one need to differentiate colours well. In this case one should use luminiscent lamp of daylight. Lamps of white light have spectrum rich on yellow rays. That’s why while using true lamps great capacity for eye work is presented, and skin colour looks great. That’s why lamps of white light are used in schools, lecture rooms, settlements, and wards of hospitals. Spectrum of lamps of warm-white light is rich on yellow and rose radiation. This fact makes less capacity for eye work, but makes the skin colour very pleasant. Variety of spectrum is one of the hygienic advantages of these lamps light returning of luminiscent lamps is in 3-4 times higher than light returning of bulbs. That’s why they are more economic. During numerous comparative investigations with bulbs on industrial plants, in schools, hospitals, lecture rooms objective induces, which characterise the nervous system state, weariness of eye, capacity for work almost in all cases prove hygienic advantage of luminiscent lamps. But for their wide usage we need professional help. It is necessary to choose the lamp correctly, according to its spectrum, taking into consideration purpose of the place.

Methods of definition of artificial lighting.

Artificial lighting can be defined by means of calculate methods, for example the methods of middle horizontal lighting. The principle of the methods is the following: if we use 10 Vat of electro energy stress on each square meter of floor, we receive the middle horizontal lighting. It depends on the force of used lamps. While the same expenditure of energy on square unit lighting can be different. It can be explained by different lighting returning of lamps of different force. Using data about lighting while expending energy (10 Wt/m2 ) and taking into consideration that received lighting depends directly on expended energy, one can find artificial lighting. For this we use the quantity of lamps with certain power and quantity of chalendeliers with certain power, which it is necessary for certain lighting. For example, it is necessary to find middle horizontal lighting in classroom. Its floor’s square is 50 m2. . We also know that 6 chalendeliers are used. The force of each lamp is 200 Wt. The voltage in net is 120 V. Taking into concideration all the conditions, general electro energy force, which is used to shine the classroom is 200 x 6 =1200 Wt. On 1 m2 of floor we have 1200:50 = 24 Wt/m2.  For lamps 200 Vat in case of energy expenditure 10 Vat/m2 lighting E will be 35,5 Lk. The lighting will be higher in so many times, as the energy expenditure is higher then common on square unit:

Proper power (Wt2) of general illumination

Height of hanging of lamps, м

Square of the apartment


Level of illumination, lux










Luminescence lamp




















































More 300










Incandescent lamp (bulb lamp)




















































More 300











Hygienically norms of artificial illumination



Minimal illumination, lx

Luminescence lamp

Incandescent lamp

(bulb lamp)

Оperation  room



Doctors room

300 (200)

150 (100)

Room for patient



Study rooms, laboratory room







Methods of determination of the natural lighting indices in different premises


Descriptive data:

1.   External factors that influence natural lighting in different premises:

- the territory latitude and its climate (number of sunny and cloudy days);

- season of the year and time of the day, when the premises are being used, existence of objects producing shadow (buildings, trees, hills, mountains).

2. Internal factors:

- name and function of premises;

- window orientation, floor;

- type of natural lighting, (light aperture location), (one-side, two-side, upper and combined);

- number of windows, their construction (one-framed, two-framed, combined);

- clarity and quality of glass, existence of objects producing shade (flowers and curtains);

- the window-sill height, distance from the window top edge to the ceiling;

- brightness (reflection ability) of the ceiling, walls, equipment and furniture

The above mentioned factors also influence the premises insolation regimen (the duration of exposure to the direct solar light). It can also be influenced by the windows’ orientation. (table 1).

Table 1

Types of premises isolation regimen

Premises insolation regimen

Orientation of windows

The duration of insolation, hours

The insolated area of the floor,%


South-East, South-West




South, East, West




North-East, North-West, West

less than 3

till 30


According to the hygienic norms the duration of insolation in residential areas, classrooms and other premises of similar functions must be not less than 3 hours.

The assessment of natural lighting in different premises using thegeometric method:

1.   The lighting coefficient determination (the ratio of the glazed part area to the floor area, expressed in common fraction);

- the total area of the glazed window part is to be measured (S1), m2;

- the area of the floor is to be measured (S2), m2;

- the lighting coefficient is to be measured (LC=S1:S2=1:n)(nis calculated as S2 divided on S1 and approximated to the integer).

The received result is assessed according to the hygienic norms (table 2).


Table 2

 The natural lighting norms for different premises

The type of premises

The daylight factor (DF)

The lighting coefficient (LC)

The angle of incidence (a)

The aperture angle (g)

The depth coefficient of premises

not less than

not less than

not less than

not less than



1:4 – 1:5






1:5 – 1:6




3. Wards


1: – 1:8




4. Surgeries


1:2 – 1:3





2. Determination of the angle of incidence a (the ABC angle at the furthest workplace from the window is formed by the horizontal line (or plane) AB from the workplace to the lower window edge (window-sill) and the line (plane) AC from the workplace to the upper window edge) (fig. 4.1).



Fig. 4.1. Diagram for determination of the angle of incidence and the angle of aperture


The aperture angle calculation:

tga=BC/AB (see table of tangents), a - the angle of incidence;

tgb=BD/AB (see table of tangents), b - the angle of shading;

Ðg=Ða-Ðb, Ðg is the angle of aperture.

Conventional marks:

BC- the height from the upper window edge to the work plane level, m;

AB- the distance from the window to the furthest work place, m;

BD- the distance from the projection of the shadowing object’s top onto the window glass to the level of the worktop, m.


As this angle together with the window glass line form the right triangle, it must be determined by tangent – the ratio of the window height above the workplace level (BC) (opposite cathetus of the triangle) to the distance from the window to the workplace (AB) (adjacent cathetus of the triangle). The angle of incidence a is found by the tangent value using the table 3.

Table 3


The trigonometric table


angle, 0


angle, 0


angle, 0



























































































3. The aperture angle g  determination (CAD angle, under which the part of the sky can be seen from the working place). This angle can be determined as the difference between the angle of incidence a and angle of shading b (DAB angle at the workplace between the horizon and the plane connecting the workplace and the shading object’s top (buildings, trees, mountains) (see the diagram, fig. 4.1).

To determine the angle of shading you must find the point D, where the line (plane) connecting the workplace and the top of the shading object comes through the window, divide the BD cathetus by AB (find the tangent of the shading angle), and find the value of the angle of shading b from the table.

4. The determination of depth coefficient in different premises - the ratio of the distance from the window to the opposite wall (EF, m) to the upper window edge height above the floor (CE, m). According to the hygienic norms this coefficient must not be higher than 2 for residential areas, classrooms and other similar premises.

The lighting engineering method of natural lighting assessment in different premises consists in determination of daylight factor (DF).

The daylight factor (DF) is defined as the ratio of the actual illuminance at a point in a room (lux) and the illuminance available from an identical unobstructed sky:



The indoor and outdoor lighting is measured by luxmeter (see the instruction, appendix 2 and fig. 4.2).


Fig. 4.2. Luxmeter U-116 (Ю-166)

(1 – measuring device (galvanometer); 2 – light receiver (selenium photo-cell); 3 – changing light filters)

The part of the sky can be hidden behind the tall buildings and trees in the cities or by mountains in highlands. That’s why the curves of the regional lighting climate are used in practice (fig. 4.3). 

The curves, shown on the fig.4.3, include months, hours and the level of cloudiness. The ordinate axis has lighting indicators, marked in thousands of lux.

The natural lighting of factory sections may be side (one-side, double-side), upper (light apertures in the ceilings) and combined.

According to the Building Norms and Rules (BNandR)-4-79, the daylight factor (DF) is calculated:

- in case of one-sided lighting – at the distance of 1 m from the opposite wall;

- in case of double-sided lighting - in the middle of the section;

- in case of the combined lighting, the average of the several lighting measurings, performed using the “envelope” method is calculated (table 4).

Table 4



on lighting determination using the luxmeter


The U-116 (Ю-116) or U-117 (Ю-117) luxmeter consists of selenium photo-cell with changing light filters and the galvanometer with the scale. When the light strikes the photo-cell surface, it produces the electric current, the strength of which is measured by the galvanometer. The galvanometer indicates the value of the researched light in luxes.

The front panel of the luxmeter also contains the switching buttons, and the scheme, that explains the effect of each button when using different light filters. There are two different scales at the device’s panel: the 0 – 100 scale, and the 0-30 scale. Each of them has the starting point of its measuring range marked: on the 0-100 scale that is 20, and on the 0-30 scale – 5. Also there is the screw-adjusted regulator for setting the device to zero.

The selenium photo-cell connected to the device with the plug is hidden in the plastic case. The spherical light filter, made of white light dispersing plastic and the opaque ring, is used with the photo-cell for more exact measuring. This filter is used simultaneously with one of the three changing filters. These changing filters have different attenuations (10, 100 and 1 000), and they extend the measuring range.

The process of the measuring consists of the following:

1)     The device is set to 0;

2)     By trying the different combinations of the pressed buttons and changing filters, the appropriate scale for the present light is found. When the button, next to which the ranges, divisible by 3 are written, the 0-30 scale is used. When the button with the ranges, divisible by 10 is pressed – the 0-100 scale is used;

3)     The measuring result in scale marks is then multiplied by the attenuation value of the filter used.


The U-116 (Ю-116) or U-117 (Ю-117) luxmeter is graded for measuring the light, produced by the incandescent lamps. The correcting coefficients are used for the other types of light. For the natural light its value is 0.8, for the fluorescent daylight lamps – 0.9, and for the white lamps – 1.1.

The general assessment of the natural lighting in different premises is made by comparing the results of all measurements with the hygienic norms. The accuracy of visual work is the base for these norms. It includes the sizes of the visual objects, their contrast against the background etc.

For the convenience the results of measurements and the hygienic norms are written into the table:


Results of determination

Hygienic norm













To draw the final conclusion about the natural lighting of different premises it is necessary to compare the assessment of each result with the norm.  

Physical characteristics of artificial illumination

1. The artificial illumination (same as natural) is characterized by:

- light intensity (I)- the light source capacity, measured in candles (Cd). It’s a light intensity, that generates the monochrome radiation of the 5401012Hzfrequency in certain direction, with radiant intensity in that direction of 1/683Wt/steradian;

- light flow (luminous flux) (F)- the density of light, measured in lumens (lm)- light flow, radiated by the individual source with intensity of 1 cd in the solid angle of 1 steradian. The solid (spatial) angle is the cone, which, if its top is considered to be in the center of the sphere, cuts the surface, equaling to the squared radius of that sphere from it;

- illuminance (E)- the amount of light falling on a surface (surface density of the light flow) , where S is the illuminated surface area, m2. The illuminance is measured in luxes. 1 lux is the illuminance of the 1 m2 surface, illuminated by the light flow of 1 lumen;

- brightness (B) –light intensity, at which the light is radiated or reflected from the surface in certain direction. , where  is the angle between the light direction and the perpendicular to the surface.

The unit of brightness is cd/m2- the brightness of the surface with the area of 1m2, radiating or reflecting the light with the intensity of 1cd;

- reflection coefficient (β) - the ratio of the reflected light flow (Fref) to the light flow received by the surface (Frec). It is calculated using the following formula .

The β value is 0.9 for fresh snow, 0.7–for white paper and 0.35 for untanned skin.

- optical transmission coefficient(τ) is the light flow, which goes through the (Fthrough.) medium, divided by the light flow, which falls on that medium .

This coefficient allows assessing the quality and the cleanness of the window glass and the glass parts of different lightingfixtures.

-luminosity (M) – surface density of the light flow, expressed in lm, which is radiated from the 1m2 surface (lm/m2).

2.                                                                                                                                   Human vision

- visual acuity (the recognition ability) is the ability of the visual analyzer to recognize the smallest elements of the object. It’s determined by the smallest angle, under which the two adjacent spots are recognized as separate. The visual acuity is conventionally considered to equal to one angular minute. The visual acuity grows proportionally to the illuminance until it reaches 130-150lux. When the illuminance is above that point, the visual acuity growth slows down.

- contrast sensitivity is the ability of the visual analyzer to perceive the minimum difference between the brightness of the object and the background. It reaches its highest level when the illuminance is 1 000-2 500 luxes;

- visual perception speed is the time, required to recognize the details of the object. This speed grows until the illuminance reaches 150 luxes. After that point, the growth slows down unproportionally to the illuminance growth;

- visibilityis the integral function of the visual analyzer, which is the combination of its main functions – visual acuity, contrast sensitivity, visual perception speed;

- clear vision stability is the time, during which the object can be clearly seen to the total time of the object examination. Physiologically this function of the visual analyzer based on the destruction of the visual purple (rhodopsin) under the influence of the light and formation of the protective black pigment on those parts of the retina, where the picture is the brightest. This function reaches its optimal value at the illuminance of 600-1 000 luxes. Its reduction is the evidence of the visual analyzer fatigue;

- color recognition function. White, black, grey – achromatic colours are only characterized by brightness and light flow intensity. Chromatic colours (monochromatic) are characterized by brightness and chromaticity. Vision is the most sensitive to the yellow and green part of the visual spectrum and the least sensitive to the violet light. During the twilight or under the artificial illumination (especially with incandescent lamps) the visual analyzer’s colour recognition reduces and may distort;

- adaptationis visual analyzer’s ability to reduce its sensitivity during the change from low to high illumination (light adaptation), (achieved very quickly, (in 2-3 minutes) and is caused by the visual purple conversion into the protective black pigment in the retina), and to increase it again when the illumination changes from high to low level (adaptation to darkness), which takes much longer – up to 40-60 minutes and is caused by the restoration of the visual purple in the retina;

- accommodationisthe ability of the eye to regulate the visual acuity depending on the distance to the examined object and illumination due to the changes in the light refraction in the optic system of the eye, which is mostly caused by the chrystalline lens curvature change. The curvature will increase when the illumination is less than 100-75luxes. So, in such circumstances the object must be closer to the eye for the proper recognition;

The insufficient illumination leads to the overstrain of accommodation system, overstrain of the visual analyzer, and for children and adolescents (their eye has not yet formed completely) it may cause the myopia (short-sightedness) especially if they have the congenital disposition;

- critical flicker frequency is determined by the time, during which the afterimage remains in the visual analyzer: the image of an object, which has disappeared from the visual field still remains visible for some time depending on the object brightness. This visual function is based on the same processes of visual purple destruction and restoration. The cinema, one of the most important human inventions, is based on it. The frequent change of the frames and the almost similar objects (25 frames per second), and the darkening of the screen provides dynamic and continuous picture.

The sources of artificial illumination may be electric and non-electric. Non-electric sources are kerosene, carbide lamps, candles and gas lamps. Their use nowadays is mostly limited to the field conditions and emergency situations. The electric sources of artificial illumination may be arc lamps (in searchlights, floodlights, spotlights etc), incandescent lamps, gas-discharge lamps and luminescent lamps.

The disadvantage of incandescent lamps is the spectrum parallax in the yellow-red direction, the distortion of the color perception, the dazzling (blinding) effect of direct rays.

The luminescent lamps have the spectrum, almost similar to the day light with modifications, depending on the luminophor, that covers the internal surface of the glass tube and transforms the ultraviolet luminescence of mercury vapour in the tube into the visible light. There are the daylight lamps (DL), white light lamps (WL), warm white light lamps (WWL) etc.

The disadvantage of luminescent lamps is the stroboscopic effect - the flickering of moving objects.

One of the disadvantages of both the direct sunlight and bright sources of artificial illumination is their ability to cause the dazzling effect. We protect ourselves from the bright sunlight using the curtains and jalousies, dark-toned windows, the sun glasses.

The lighting fixtures (also used for the aesthetic purpose), are used for protection from the dazzling effect of artificial light sources.

The lighting fixtures are divided onto 5 types according to light flow formation (see fig. 5.1):

- direct light type, directing the whole light flow into one hemisphere (the table lamp with the opaque lamp-shade, spotlights, floodlights, and other fixtures used in photo and movie shooting);

- evenly-diffusing the light (dim or light-white sphere);

- reflected light (when the lamp with the opaque lamp-shade directs the light flow towards the upper hemisphere);

- directed-diffused light type, when the main light flow is directed towards the lower hemisphere through the aperture in the lamp-shade and the other part is diffused to the upper hemisphere through the lamp-shade made of plastic, dim or light-white glass;

- reflected-diffused light type, when the main light flow is directed towards the upper hemisphere and is reflected from the ceiling but a part of it is diffused to the lower hemisphere through the lamp-shade with dim or light-white glass.

The allowable values of dazzling at the workplace are:

-20 cd/m2 for types 1 and 2 of the visual work;

-40 cd/m2 for the types 3-5 of the visual work;

- 60 cd/m2 for the types 6 and 7 of the visual work.


Fig.5.1. Types of lighting fixtures

(1 - direct light type, 2 - directed-diffused light type; 3, 4 - evenly-diffused light type; 5 - reflected-diffused light type)


The scheme of the artificial illumination assessment in different premises

Descriptive data:

-                    name and function of premises;

-                    system of illumination (local, general and combined);

-                    number of lights, their types (incandescent, luminescent and other lamps);

-                    their capacity, Wt;

-                    type of lighting fixture, light flow direction and formation (direct, evenly-diffused, directed-diffused, reflected, diffused-reflected);

-                    height of the lamps above the floor and the work plane;

- illuminated area;

- reflection ability (brightness) of ceiling, walls, windows, floor, furniture and other surfaces.


Illumination determination using the ‘Watt’ calculation method:

a)     the area of the premises is determined, S, m2;

b)    the total capacity of all the lamps, Wt, is determined;

c)     the specific capacity, Wt/ m2, is calculated;

d)    the illuminance at the specific capacity of 10Wt/m2 can be found from the table 1 of minimum horizontal illuminance values;

e)     for the incandescent lamps the illuminance is calculated according to the following formula:

where, P –is a specific capacity, Wt/m2;

Etab- illuminance at 10Wt/m2, (from table 1);

    K – which equals to 1.3, is the reserve coefficient for residential and public premises.

The (Etab) minimum horizontal illuminance values at the specific capacity (P) of 10 Wt/m2

The electric lamp capacity, Wt

The direct light

Half-reflected light

Voltage, V








































This formula may be applied for the illumination calculation if all the lamps have the same capacity.The calculations are done separately if there are lamps with different capacity. Their results are added up. The received illumination value by the “Watt” method is compared to the normative values (table 2).

Table 2

Standards of the general artificial illumination (BNaR II-69-78 and BNaR II-4-79)


The smallest illumination, lux

Luminescent lamps

Incandescent lamps

Rooms and kitchens of dwelling houses






Rooms of technical drawing



School workshops



Public reading halls



Operating and sectional rooms



Delivery room, dressing ward, manipulation room






Surgeon’s, obstetritian-gynecologist’s, pediatrician’s, infectionist’s, dentist’s room



X-ray room



Functional diagnostics room



Wards for newly-born babies, postoperative rooms




For the luminescent lamps with 10 Wt/m2 specific capacity the minimum horizontal illumination is 100 luxes. The minimum horizontal illumination for other specific capacities is calculated proportionally.

For the industrial areas, according to BNandR II-4-79, all activities are divided into seven types of work, based on the linear dimensions of the smallest object, worked with at the distance of 0.5 m from the eye. The first 5 types are divided into 4 sub-types (a, b, c, d), based on the contrast between the examined object and the background, and the background luminosity. For example, during the especially accurate work (type 1, the object size is less than 0.1 mm), the illumination at the workplace must be 1 500luxes if the contrast with the background is low; 1 000 luxes if the contrast is medium and 400 luxes if the contrast is high. When the work is of low accuracy (type 4, object size is 1.0-10 mm ), the illumination must be 150,100, 75luxes respectively.

The above mentioned method is not fully precise as it doesn’t take the illumination in each point, lamp location and some other factors into the account, but is often used for the classes, wards and other areas illumination assessment.

To determine the illumination at the definite workplace, the lamp specific capacity (P) must be multiplied by the coefficient (e), which shows the amount of luxes, given by the 1 Wt/m2 specific capacity: E=P×e. This coefficient for the premises of 50m2 area and the lamp capacities of less than 110 Wt is 2, 110 Wt and more – 2.5 (see table 3) and 12.5 for the luminescent lamps.

Table 3

The values of the coefficient e

Lamp capacity, Wt

Voltage, V



less than 110



110 and more



Illuminance determination using the luxmeter.

The determination of horizontal illuminance at the workplace is done with the help of luxmeter (see topic 4, appendix 2). The 0.9 correction coefficient is used for the luminescent lamps of day illumination (LD); 1.1 - for the white lamps; 1.2-for the mercury-discharge lamps, because the device has initially been intended for measuring of the illuminance, produced by incandescent lamps.

If the determination is done in the morning or in the afternoon, it’s necessary to determine the illuminance, produced by the mixed illumination (both natural and artificial). After that the determination is done when the artificial illumination is switched off. The difference between the received data is the value of illuminance, produced by the artificial illumination.

The illumination evenness is determined by the “Envelope method,” which means that illuminance is measured at 5 different points of the premises and evaluated by calculation of illuminance variety coefficient (minimum illuminance divided by the maximum illuminance at two different points, which are 0.75 m from each other, when the evenness is determined at the workplace, or 5 m from each other, if the evenness is determined in the whole room).

The calculation of the workplane brightness is made using to the formula:

where,B-is brightness, cd/m2;

E-illumination, lux;

C-coefficient of surface reflection

(0.7-white; 0.5 - light-beige; 0.4-brown; 0.1-black).

The allowable brightness of general illumination lamps for residential and public premises is given in the table 4.


The allowable brightness values of general illumination lamps for residential and public premises


The allowable brightness value, cd/m2

for incandescent lamps

for luminescent lamps

The main premises of dwelling and public buildings

15 000

5 000

Classrooms, training rooms, lecture-halls, reading-halls, libraries

5 000-8 000

5 000-8000

Doctor’s room

15 000


Wards, special rooms of children institutions and boarding-schools

5 000

5 000


The height of the lamps above the floor and the working place, and the location of general light lamps in the horizontal plane of premises is of the great importance for creating the sufficient and even illumination, and for the protection from dazzling. When the illumination is general or combined, the lamps of general light are located evenly in the horizontal plane of the ceiling (when it is necessity to create sufficient illuminance in every point of premises), or they are locally concentrated (to create the high illuminance in certain parts of the room). The lamp height above the floor must be not lower, than values, given in the table 5 to minimize the dazzling effect of the lamps.

The best illumination conditions are created when the optimal ratio between the distance between the lamps in horizontal plane (L), and their height above the work-plane (H) is used. These ratios have been found as a result of the determination of the light distribution curves of different lamps. The optimal values are shown in table 6.

Table 5

The lowest height of the lamps above the floor (m)

Lamps characteristics

Incandescent lamps

Luminescent lamps (depending on the amount of lamps in the fixture)

200Wt and less capacity

capacity more than 200 Wt

4 and less

more than 4

Direct light lamps

with diffusing reflectors:





a) protective angle from 10° to 30°;





b) protective angle more than 30°





Lamps of diffused light with the light diffusers transparency:





a) less than 55%





b) from 55 to 80%






Table 6

The optimal ratios between the distance between the lamps and their height above the work-plane (L/H)

The lamp type


“Universal” without a shade, with opal shade


Direct light “Lucetta”, enameled narrow angle fixture


Enameled narrow angle fixture


The sphere of light-white silicate or organic glass



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