Light flux can only be measured in laboratory conditions, otherwise it is simply impossible to determine the level of illumination. However, devices for each room already have certain markings, based on which it is possible to calculate the degree of illumination of the room, expressed in lighting units. The main conditions are to know the area and have basic calculation skills.

Main characteristics of light

Light is a physical quantity, which has such properties as luminous flux power, luminosity, luminous intensity, illumination and brightness.

The power of the luminous flux, that is, visible light radiation, can be assessed by the perceived effect of light on human vision. The unit of measurement for luminous flux is lumen.

An ordinary 100-watt incandescent lamp has a power rating of 1350 lumens, while a fluorescent lamp of the same “wattage” shows much more - 3200 lumens.

In more detail, one point source with a luminous intensity of 1 candela emits light flow 1 lumen power. The solid angle in this case has a value of 1 steradian.

The next characteristic of light is its strength, which characterizes the flux density; this value is measured in candelas. Very generally, it was previously believed that 1 cd is equal to the light of 1 candle; this unit was even equated to 1 W. You can increase the light intensity by installing a concave mirror reflector on one side of the light bulb.

As for brightness, this value is expressed in terms of the candela per square meter ratio. m, that is, the projection of the luminous flux onto a flat illuminated surface at a right angle. Luminosity, or luminosity, reflects the density of light flux relative to the area of ​​the illuminated surface - 1 lumen per square meter. m.

Such a characteristic of light as illuminance demonstrates the surface density of light illuminating a certain surface area. This value is expressed through the ratio li/sq. m. In physics, there are special units in which illumination is measured - lux.

Features of calculation

When calculating the degree of illumination of any room, it is necessary to take into account the law of additivity. It works when there are several light sources affecting a certain area.

The law of additivity is expressed in the summation of illumination produced by each light object separately:

∑ E = E1 + E2 +… + En.

The illuminance index only applies to surfaces that reflect light rather than emit their own light. For example, the moon, walls, floor and any other planes. Room illumination is measured as follows:

• For a room with dimensions of 3x3x3 m, provided it has a five-watt LED with a power of 100 lumens, it is necessary to calculate the total area of ​​​​all illuminated surfaces - floor, ceiling and walls, and then divide the luminous flux by the area.
• Get 100 lumens/9 sq. m * 6=100/54= 1.85 lux - units of illumination measurement.
• If the light source is equipped with a special lens, thanks to which a circle with a diameter of, for example, 1 m will be brighter illuminated on one of the surfaces (the area of ​​the circle, accordingly, will be equal to 0.78 sq. m), then the illumination of this area will have a value of 128 lux .

There are also fairly standard indicators - under certain conditions, light shows approximately the same values, so similar situations can be generalized. Some examples of illumination include the following:

Measuring device

There is a special device for measuring the level of surface illumination- lux meter. Its device includes a photocell that captures light. The operating mechanism of a lux meter can be either digital or analogue - in both cases the measurement accuracy is quite high. GOST assumes a maximum error of about 10%.

In many designs, the section containing the photocell is connected to the rest using an elastic twisted wire to allow work in hard-to-reach places. The device is equipped with light filters, using which you can adjust the measurement process, taking into account the special nuances of the terrain.

When working with the device, it should be positioned horizontally - any deviations from this plane may negatively affect the accuracy of measurements. It is also necessary to avoid the influence of random shadows. Detailed methods for each type of lighting are described in the corresponding state standard.



Lux (unit of illuminance) Lux(from Latin lux ≈ light), unit of illumination in International System of Units. Abbreviated designation: Russian lk, international lx. 1 L. ≈ illumination of a surface with an area of ​​1 m2 with a luminous flux of radiation incident on it equal to 1 lm. ═ 1 L. = 10-4 phot (unit of illumination GHS system of units).

Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what "Lux (unit of illumination)" is in other dictionaries:

Lux (symbol: lx, lx) is a unit of measurement of illumination in the SI system. Lux is equal to the illumination of a surface with an area of ​​1 m² with a luminous flux of radiation incident on it equal to 1 lm. Multiples and submultiples Decimal multiples and submultiples ... Wikipedia

1. lux, constant (luxuriously equipped); cabinlux 2. luxury, a (hotel room, cabin, compartment, etc. of the highest category); live in a suite 3. suite, a; R. pl. ov, counting f. lux (unit of illumination) ... Russian word stress

1. LUX, a; m. [from lat. lux light] Phys. Unit illumination measurements. 2. LUX [from French. luxe luxury]. I. unchanged; in sign. adj. Luxuriously, comfortably equipped, distinctive high quality. Coupe l. Cabin l. Hotel l. II. A; m. Razg... ... encyclopedic Dictionary

1) (Latin lux light) a unit of illumination in the international system of units (si), equal to the illumination of a surface with an area of ​​1 m2 with a luminous flux of radiation incident on it equal to 1 lumen; abbr. designations: lx, lx. 2) (French luxe luxury lat.… … Dictionary of foreign words of the Russian language

LUX, ah, husband. (specialist.). Unit of illumination. II. LUX 1. a, husband The best hotel room, carriage, salon, cabin in terms of equipment and service. Live (drive, sail) in a luxury. 2. unchangeable Highest class, category, grade. Cabin l. Chocolate l. Atelier l. |… … Ozhegov's Explanatory Dictionary

LUX 1, a, m. (special). Unit of illumination. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

This term has other meanings, see Lux (meanings). The request "lk" is redirected here; see also other meanings. Lux (from Latin lux light; Russian designation: lk, international designation: lx) unit of measurement... ... Wikipedia

I (French luxe luxury, splendor, from the Latin luxus splendor) designation of luxuriously equipped stores, hotels, compartments, cabins, and some goods. II (from the Latin lux light) unit of illumination in the International System... ... Great Soviet Encyclopedia

Light and radiation
By light we mean electromagnetic radiation, causing a visual sensation in the human eye. In this case, we are talking about radiation in the range from 360 to 830 nm, which occupies a tiny part of the entire spectrum of electromagnetic radiation known to us.
Luminous flux F
Unit of measurement: lumen* [lm]. Luminous flux Ф is the entire radiation power of a light source, estimated by the light sensation of the human eye. A conventional 100 W incandescent lamp produces a luminous flux of approximately 1300 lm. A compact fluorescent fluorescent lamp with a power of 26 W creates a luminous flux of approximately 1600 lm. The luminous flux of the Sun is 3.8? 1028 lm.
Luminous Intensity I
Unit of measurement: candela** [cd]. The light source emits luminous flux F in different directions with different intensities. The intensity of light emitted in a certain direction is called luminous intensity I.
Illumination E
Unit of measurement: lux*** [lx]. Illumination E reflects the ratio of the incident luminous flux to the illuminated area. Illumination is equal to 1 lux if the luminous flux of 1 lm is evenly distributed over an area of ​​1 m2
Brightness L
Unit of measurement: candela per square meter[cd/m2]. The luminous brightness L of the light source or illuminated area is the main factor for the level of light sensation of the human eye.
Colorful temperature
Unit of measurement: Kelvin**** [K]. The color temperature of the light source is determined by comparison with the so-called "black body" and is displayed by the "black body line". If the temperature of the “black body” increases, then the blue component in the spectrum increases, and the red component decreases. An incandescent lamp with warm white light has, for example, a color temperature of 2700 K, while a fluorescent lamp with daylight color has a color temperature of 6000 K.

Common colors of light
There are the following three main colors of light: warm white 5000 K.

Color rendition
Depending on the location of the lamps and the task they perform, artificial light should provide the best possible color perception (as with natural daylight). This capability is determined by the color rendering characteristics of the light source, which are expressed in terms of different degrees of "general color rendering index" Ra. Color rendering index reflects the level of correspondence between the natural color of a body and the visible color of that body when illuminated by a reference light source. To determine the value, the Ra color shift is recorded using the eight standard reference colors specified in DIN 6169, which is observed when the light of the light source under test is directed towards these reference colors. The smaller the deviation of the color of the light emitted by the lamp under test from the reference colors, the better the color rendering characteristics of this lamp. A light source with a color rendering index of Ra = 100 emits light that optimally reflects all colors, like the light of a reference light source. The lower the Ra value, the worse the colors of the illuminated object are reproduced.

* One lumen is equal to the luminous flux emitted by a point isotropic source, with a luminous intensity equal to one candela, into a solid angle of one steradian (1 lm = 1 cd x sr). The total luminous flux created by an isotropic source with a luminous intensity of one candela is equal to 4n lumens.

** Candela (designation: cd, cd; from Latin candela - candle) is equal to the intensity of light emitted in a given direction by a source of monochromatic radiation with a frequency of 540·1012 hertz, the energy intensity of which in this direction is (1/683) W /avg.

*** Lux (designation: lux, lx) - a unit of illumination measurement, equal to the illumination of a surface with an area of ​​1 m? with a luminous flux of radiation incident on it equal to 1 lm

**** Kelvin (designation: K) is a unit of measurement of temperature, one kelvin is equal to 1/273.16 of the thermodynamic temperature of the triple point of water. The beginning of the scale (0 K) coincides with absolute zero. Conversion to degrees Celsius. C = K - 273.15

Light is something without which nothing on Earth would be able to exist. Like all physical quantities, it can be calculated, which means there is a unit of measurement for luminous flux. What is it called and what is it equal to? Let's find answers to these questions.

What is "luminous flux" called?

First of all, it is worth understanding what this term is called in physics.

Luminous flux is the power of light emission, assessed by the light sensation it produces from the point of view of the human eye. This is a quantitative characteristic of the radiation of a light source.

The numerically considered quantity is equal to the energy of the light flux passing through a certain surface per unit time.

Luminous flux unit

How is the physical quantity in question measured?

According to current standards The SI (International System of Units) uses a specialized unit called the lumen.

This word was derived from the Latin noun meaning "light" - lūmen. By the way, this word also gave rise to the name of the secret organization “Illuminati,” which became a subject of general interest several years ago.

In 1960, the lumen officially began to be used throughout the world as a unit of measurement of luminous flux, and remains so to this day.

In abbreviated form in Russian, this unit is written as “lm”, and in English - lm.

It is worth noting that in many countries the light power of light bulbs is measured not in watts (as in the vast expanses of the former USSR), but rather in lumens. In other words, overseas consumers consider not the amount of energy consumed, but the strength of the light emitted.

By the way, because of this, the packaging of most modern energy-saving light bulbs contains information about their characteristics in both watts and lumens.

Formula

The unit of measurement of luminous flux under consideration is numerically equal to light from a point isotropic source (with a force of candela) emitted into a solid angle equal to one steradian.

In the form of a formula, it looks like this: 1 lm = 1 cd x 1 avg.

If we take into account that a complete sphere forms a solid angle of 4P sr, it turns out that the total luminous flux of the above source with a power of one candela is equal to 4P lm.

What is "candela"

Having learned what a lumen is, you should pay attention to the unit associated with it. We are talking about CD - that is, candela.

This name was derived from the Latin word for “candle” (candela). From 1979 to this day it is according to the SI (International System of Units).

In fact, one candela is the intensity of light emitted by one candle (hence the name). It is worth noting that in the Russian language for a long time, instead of the term “candela”, the word “candle” was used. However, this name is outdated.

From the previous paragraph it is clear that lumen and candela are related (1 lm = 1 cd x 1 sr).

Lumens and Luxes

When considering the features of such a light value as a lumen, it is worth paying attention to such a close concept as “lux” (lx).

Like candelas with lumens, luxes also refer to lighting units. Lux is a unit of illumination used in the SI system.

The relationship between lux and lumen is as follows: 1 lux is equal to 1 lm of luminous flux, evenly distributed over a surface of 1 square meter. Thus, in addition to the above lumen formula (1 lm = 1 cd x 1 sr), this unit has one more: 1 lm = 1 lx/m2.

In simpler terms, a lumen is an indicator of the amount of light emitted by a certain source, for example, the same light bulb. But lux shows how light the room really is, since not all light rays reach the illuminated surface. In other words, lumen is the light that came out of the source, lux is the amount of it that actually reached the illuminated surface.

As already mentioned, not all the emitted light always reaches the illuminated surface, because often in the path of such rays there are obstacles that create shadows. And the more there are on the way, the less illumination there is.

For example, when the library hall was built, many light bulbs were hung in it. General illumination this empty room was equal to 250 lux. But when renovation work were completed and furniture was brought into the hall, the light level dropped to 200 lux. This is despite the fact that the light bulbs, as before, produced the same amount of lumens of light energy. However, in the path of each of its rays, obstacles now appeared in the form of shelves with books and other library furniture, as well as visitors and workers. Thus, they absorbed part of the emitted light, reducing the total amount of illumination to the hall.

The situation given as an example is not an exception of its kind. Therefore, when constructing any new buildings or decorating the interior of existing ones, it is always important to take into account its illumination. Most institutions even have a system of lighting standards; naturally, it is measured in lux.

IN modern world There are several programs in which you can not only simulate the design of your room yourself, but also calculate how light it will be. After all, the vision of its inhabitants depends on this.

Lumen and Watt

In the past, in our country, when choosing a light bulb, we were guided by the number of watts it consumes. The more of them, the better the light of this device.
Today, even in our country, radiation power is increasingly measured in lumens. In this regard, some believe that lm and W are quantities of the same kind, which means that lumens to watts and vice versa can be freely converted, like some other SI units.

This opinion is not entirely correct. The fact is that both units of measurement under consideration are used for different quantities. So, a watt is not a light unit, but an energy unit that shows the power of a lighting source. While lumen shows how much light a particular device emits.

For example, a regular incandescent lamp that consumes 100 watts produces 1340 lumens of light. At the same time, its more advanced (today) LED “sister” produces 1000 lm while consuming only 13 W. Thus, it turns out that the light intensity of a light bulb is not always directly dependent on the amount and power of energy absorbed by it. The substance used for lighting in the device also plays an important role in this matter. This means that there is no direct relationship between lumens and watts.

Moreover, these quantities are really related to each other. The luminous efficiency of any light source (the relationship between the energy consumed and the amount of light produced) is measured in lumens per watt (lm/W). It is this unit that is evidence of the effectiveness of this or that lighting fixture, as well as its efficiency.

It is worth noting that if necessary, it is still possible to convert lumens to watts and vice versa. But for this you need to take into account several additional nuances.

• The nature of the light source. Which lamp is used in the calculations: incandescent, LED, mercury, halogen, fluorescent, etc.
• Light output of the device (how much watt it consumes and how many lumens it produces).

However, in order not to complicate your life, to carry out such calculations, you can simply use an online calculator or download a similar program to your computer or other device.

Multiples of Lumen Units

Lumen, like all its “relatives” in the SI system, has a number of standard multiples and submultiples. Some are used for ease of calculation when one has to deal with either too small or too large values.

If we are talking about the latter, then they are written in the form of a positive degree, if about the former - in the form of a negative one. Thus, the largest multiple unit of lumen - iottalumen - is equal to 10 24 lm. It is most often used to characterize cosmic bodies. For example, the luminous flux of the Sun is 36300 Ilm.

The most commonly used units are four multiples: kilolumen (10 3), megalumen (10 6), gigalumen (10 9) and teralumen (10 12).

Lumen subunits

The smallest submultiple unit lumen is ioctolumen - ilm (10 -24), however, like iottalumen, it is practically not used in real calculations.

The most commonly used units are millilumen (10 -3), microlumen (10 -6) and nanolumen (10 -9).

>>Illuminance

• Remember how you felt when you entered a dark room. It becomes somehow uneasy, because you can’t see anything around... But as soon as you turn on the flashlight, nearby objects become clearly visible. Those that are located somewhere further can be barely distinguished by their contours. In such cases, they say that objects are illuminated differently. Let's find out what illumination is and what it depends on.

1. Determine the illumination

A luminous flux spreads from any light source. The greater the light flux that falls on the surface of a particular body, the better it is visible.

• A physical quantity numerically equal to the luminous flux incident on a unit of illuminated surface is called illumination.

Illumination is indicated by the symbol E and is determined by the formula:

where F is the luminous flux; S is the surface area on which the luminous flux falls.

In SI, the unit of illumination is taken to be lux (lx) (from Latin Iux - light).

One lux is the illumination of such a surface, per square meter of which a luminous flux equal to one lumen falls:

Here are some surface values ​​(near the ground).

Illumination E:

Sunlight at noon (at mid-latitudes) - 100,000 lux;
sunlight in an open place on a cloudy day - 1000 lux;
sun rays in bright room(near the window) - 100 lux;
outdoors under artificial lighting - up to 4 lux;
from the full moon - 0.2 lux;
from the starry sky on a moonless night - 0.0003 lux.

2. Find out what illumination depends on

You've probably all seen spy movies. Imagine: some hero, in the light of a weak flashlight, carefully looks through documents in search of the necessary “secret data”. In general, to read without straining your eyes, you need illumination of at least 30 lux (Fig. 3.9), and this is a lot. And how does our hero achieve such illumination?

First, he holds the flashlight as close as possible to the document he is viewing. This means that illumination depends on the distance from the illuminated object.

Secondly, it positions the flashlight perpendicular to the surface of the document, which means that the illumination depends on the angle at which the light hits the surface.

Rice. 3.10. If the distance to the light source increases, the area of ​​the illuminated surface increases

And in the end, for better lighting he can simply take a more powerful flashlight, since it is obvious that as the source of light increases, the illumination increases.

Let's find out how illumination changes when the distance from a point light source to the illuminated surface increases. Let, for example, a luminous flux from a point source fall on a screen located at a certain distance from the source. If you double the distance, you will notice that the same luminous flux will illuminate an area 4 times larger. Since, the illumination in this case will decrease by 4 times. If you increase the distance by 3 times, the illumination will decrease by 9 - 3 2 times. That is, illumination is inversely proportional to the square of the distance from a point light source to the surface (Fig. 3 10).

If a beam of light falls perpendicular to the surface, then the luminous flux is distributed over a minimal area. If the angle of incidence of light increases, the area on which the luminous flux falls increases, so the illumination decreases (Fig. 3.11). We have already said that if the intensity of the light source increases, the illumination increases. It has been experimentally established that illumination is directly proportional to the light intensity of the source.

(Illumination decreases if there are particles of dust, fog, smoke in the air, since they reflect and scatter a certain part of the light energy.)

If the surface is located perpendicular to the direction of propagation of light from a point source and the light propagates in clean air, then the illumination can be determined by the formula:

where I is the luminous intensity of the source, R is the distance from the light source to the surface.

Rice. 3.11 In the case of increasing the angle of incidence of parallel rays on the surface (a 1< а 2 < а 3) освещенность этой поверхности уменьшается, поскольку падающий световой поток распределя­ется по все большей площади поверхности

3. Learning to solve problems

The table is illuminated by a lamp located at a height of 1.2 m directly above the table. Determine the illumination of the table directly under the lamp if the total luminous flux of the lamp is 750 lm. Consider a lamp as a point source of light.

• Let's sum it up

A physical quantity numerically equal to the luminous flux F incident on a unit of illuminated surface S is called illumination. In SI, the lux (lx) is taken as the unit of illumination.

The illumination of the surface E depends: a) on the distance R to the illuminated surface b) on the angle at which the light falls on the surface (the smaller the angle of incidence, the greater the illumination); c) on the luminous intensity I of the source (E - I); d) transparency of the medium in which light propagates, passing from the source to the surface.

• Control questions

1. What is called illumination? In what units is it measured?
2. Is it possible to read without straining your eyes in a bright room? outdoors under artificial light? under the full moon?

3. How can you increase the illumination of a certain surface?

4. The distance from the point light source to the surface was increased by 2 times. How did the illumination of the surface change?

5. Does the illumination of a surface depend on the intensity of the light source that illuminates this surface? If it depends, then how?

• Exercises

1. Why is the illumination of horizontal surfaces at noon greater than in the morning and evening?

2. It is known that illumination from several sources is equal to the sum of illumination from each of these sources separately. Give examples of how this rule is applied in practice.

3. After studying the topic “Lighting,” seventh-graders decided to increase the illumination of their workplace:

Petya replaced the light bulb in his desk lamp with a higher power bulb;
- Natasha put another one table lamp;
- Anton raised the chandelier that hung above his table higher;
- Yuri positioned the table lamp in such a way that the light began to fall almost perpendicular to the table.

Which students did the right thing? Justify your answer.

4. On a clear noon, the illumination of the Earth's surface by direct sunlight is 100,000 lux. Determine the luminous flux incident on an area of ​​100 cm2.

5. Determine the illumination from a 60 W electric light bulb located at a distance of 2 m. Is this illumination sufficient for reading a book?

6. Two light bulbs placed side by side illuminate the screen. The distance from the light bulbs to the screen is I m. One light bulb was turned off. How much closer do you need to move the screen so that its illumination does not change?

• Experimental task

To measure the intensity of light, instruments called photometers are used. Make a simple analogue of a photometer. To do this, take White list(screen) and place it on it grease stain(for example, oil). Fix the sheet vertically and light it from both sides different sources light (S 1, S 2) (see figure). (The light from the sources should fall perpendicular to the surface of the sheet.) Slowly move one of the sources until the spot becomes almost invisible. This will happen when the illumination of the spot on one and the other side is the same. That is, E 1 = E 2.

Because the . Measure the distance from the first source to the screen (R 1) and the distance from the second source to the screen (R 2).

Compare how many times the luminous intensity of the first source differs from the luminous intensity of the second source: .

• Physics and technology in Ukraine

Research and production complex "Fotopribor" (Cherkassy) The scope of the enterprise is the development and production of precision mechanics, optoelectronics and optomechanics devices for various purposes, medical and forensic equipment, household goods, office watches of a representative class. HBK Fotopribor develops and produces periscope sights for a variety of artillery installations, gyrocompasses, gyroscopes, optical-electronic equipment for helicopters, armored vehicles, as well as wide range optical equipment and devices for various purposes.

Physics. 7th grade: Textbook / F. Ya. Bozhinova, N. M. Kiryukhin, E. A. Kiryukhina. - X.: Publishing house "Ranok", 2007. - 192 p.: ill.

Lesson content lesson notes and supporting frame lesson presentation interactive technologies accelerator teaching methods Practice tests, testing online tasks and exercises homework workshops and trainings questions for class discussions Illustrations video and audio materials photographs, pictures, graphs, tables, diagrams, comics, parables, sayings, crosswords, anecdotes, jokes, quotes Add-ons abstracts cheat sheets tips for the curious articles (MAN) literature basic and additional dictionary of terms Improving textbooks and lessons correcting errors in the textbook, replacing outdated knowledge with new ones Only for teachers calendar plans learning programs guidelines

1. Luminous flux

Luminous flux is the power of radiant energy, assessed by the light sensation it produces. Radiation energy is determined by the number of quanta that are emitted by the emitter into space. Radiation energy (radiant energy) is measured in joules. The amount of energy emitted per unit time is called radiation flux or radiant flux. The radiation flux is measured in watts. The luminous flux is designated Fe.

where: Qе - radiation energy.

The radiation flux is characterized by the distribution of energy in time and space.

In most cases, when talking about the distribution of radiation flux over time, they do not take into account the quantum nature of the occurrence of radiation, but understand this as a function that gives a change in time of instantaneous values ​​of the radiation flux Ф(t). This is acceptable because the number of photons emitted by the source per unit time is very large.

According to the spectral distribution of the radiation flux, sources are divided into three classes: with line, stripe and continuous spectra. The radiation flux of a source with a line spectrum consists of monochromatic fluxes of individual lines:

where: Фλ - monochromatic radiation flux; Fe - radiation flux.

For sources with a striped spectrum, radiation occurs within fairly wide areas of the spectrum - bands separated from one another by dark intervals. To characterize the spectral distribution of the radiation flux with continuous and striped spectra, a quantity called spectral flux density

where: λ - wavelength.

The spectral radiation flux density is a characteristic of the distribution of the radiant flux over the spectrum and is equal to the ratio of the elementary flux ΔФeλ corresponding to an infinitesimal area to the width of this area:

Spectral radiation flux density is measured in watts per nanometer.

In lighting engineering, where the main receiver of radiation is the human eye, to evaluate effective action radiation flux, the concept of luminous flux is introduced. Luminous flux is the flux of radiation, assessed by its effect on the eye, the relative spectral sensitivity of which is determined by the average spectral efficiency curve approved by the CIE.

In lighting technology, the following definition of luminous flux is used: luminous flux is the power of light energy. The unit of luminous flux is lumen (lm). 1 lm corresponds to the luminous flux emitted in a unit solid angle by a point isotropic source with a luminous intensity of 1 candela.

Table 1. Typical luminous values ​​of light sources:

Types of lamps	Electric Energy, W	Luminous flux, lm	Luminous output lm/w
	100 W	1360 lm	13.6 lm/W
Fluorescent Lamp	58 W	5400 lm	93 lm/W
Sodium lamp high pressure	100 W	10000 lm	100 lm/W
Sodium lamp low pressure	180 W	33000 lm	183 lm/W
High pressure mercury lamp	1000 W	58000 lm	58 lm/W
Metal halide lamp	2000 W	190000 lm	95 lm/W

The light flux Ф falling on a body is distributed into three components: reflected by the body Фρ, absorbed by Фα and transmitted Фτ. When using the following coefficients: reflection ρ = Фρ /Ф; absorption α =Фα/Ф; transmission τ = Фτ / Ф.

Table 2. Light characteristics of some materials and surfaces

Materials or surfaces	Odds			Character of reflection and transmission
	reflections ρ	absorption α	transmission τ
Chalk	0,85	0,15	-	Diffuse
Silicate enamel	0,8	0,2	-	Diffuse
Mirror aluminum	0,85	0,15	-	Directed
Glass mirror	0,8	0,2	-	Directed
Frosted glass	0,1	0,5	0,4	Directional-scattered
Organic milk glass	0,22	0,15	0,63	Directional-scattered
Opal silicate glass	0,3	0,1	0,6	Diffuse
Silicate milk glass	0,45	0,15	0,4	Diffuse

2. Light power

The distribution of radiation from a real source in the surrounding space is not uniform. Therefore, the luminous flux will not be an exhaustive characteristic of the source if the distribution of radiation in different directions of the surrounding space is not simultaneously determined.

To characterize the distribution of light flux, the concept of spatial density of light flux in different directions of the surrounding space is used. The spatial density of the luminous flux, determined by the ratio of the luminous flux to the solid angle with the vertex at the point where the source is located, within which this flux is evenly distributed, is called luminous intensity:

where: F - luminous flux; ω - solid angle.

The unit of luminous intensity is the candela. 1 cd.

This is the luminous intensity emitted in a perpendicular direction by a blackbody surface element with an area of ​​1:600000 m2 at the solidification temperature of platinum.
The unit of luminous intensity is the candela, cd is one of the basic quantities in the SI system and corresponds to a luminous flux of 1 lm, uniformly distributed within a solid angle of 1 steradian (avg). A solid angle is a part of space enclosed inside a conical surface. Solid angleω is measured by the ratio of the area it cuts out from a sphere of arbitrary radius to the square of the latter.

3. Illumination

Illuminance is the amount of light or luminous flux incident on a unit surface area. It is designated by the letter E and measured in lux (lx).

The unit of illumination lux, lux has the dimension lumen per square meter (lm/m2).

Illumination can be defined as the density of luminous flux on an illuminated surface:

Illumination does not depend on the direction of propagation of the light flux onto the surface.

Here are some generally accepted illumination indicators:

Summer, day under a cloudless sky - 100,000 lux

Street lighting- 5-30 lux

Full moon on a clear night - 0.25 lux

4. The relationship between luminous intensity (I) and illuminance (E).

Inverse square law

Illumination at a certain point on a surface perpendicular to the direction of propagation of light is defined as the ratio of luminous intensity to the square of the distance from this point to the light source. If we take this distance as d, then this relationship can be expressed by the following formula:

For example: if a light source emits light with an intensity of 1200 cd in a direction perpendicular to the surface at a distance of 3 meters from this surface, then the illuminance (Ep) at the point where the light reaches the surface will be 1200/32 = 133 lux. If the surface is at a distance of 6 m from the light source, the illumination will be 1200/62 = 33 lux. This relationship is called "inverse square law".

Illumination at a certain point on a surface not perpendicular to the direction of light propagation is equal to the luminous intensity in the direction of the measurement point, divided by the square of the distance between the light source and the point on the plane multiplied by the cosine of the angle γ (γ is the angle formed by the direction of incidence of the light and the perpendicular to this plane).

Hence:

This is the law of cosine (Figure 1).

Rice. 1. To the law of cosine

To calculate horizontal illumination, it is advisable to change the last formula by replacing the distance d between the light source and the measurement point with the height h from the light source to the surface.

In Figure 2:

Then:

We get:

Using this formula, the horizontal illumination at the measurement point is calculated.

Rice. 2. Horizontal illumination

6. Vertical illumination

Illumination of the same point P in a vertical plane oriented towards the light source can be represented as a function of the height (h) of the light source and the angle of incidence (γ) of luminous intensity (I) (Figure 3).

luminosity:

For surfaces of finite dimensions:

Luminosity is the density of the luminous flux emitted by a luminous surface. The unit of luminosity is the lumen per square meter of luminous surface, which corresponds to a surface of 1 m2 that uniformly emits a luminous flux of 1 lm. In the case of general radiation, the concept of energetic luminosity of the radiating body (Me) is introduced.

The unit of energetic luminosity is W/m2.

Luminosity in this case can be expressed through the spectral energy luminosity density of the emitting body Meλ(λ)

For a comparative assessment, we reduce the energy luminosities to the luminosities of some surfaces:

Sun surface - Me=6 107 W/m2;

Incandescent lamp filament - Me=2 105 W/m2;

The surface of the sun at the zenith is M=3.1 109 lm/m2;

Fluorescent lamp bulb - M=22 103 lm/m2.

This is the intensity of light emitted per unit surface area in a specific direction. The unit of measurement for brightness is candela per square meter (cd/m2).

The surface itself can emit light, like the surface of a lamp, or reflect light that comes from another source, like the surface of a road.

Surfaces with different properties reflections under the same illumination will have different degrees of brightness.

The brightness emitted by a surface dA at an angle Ф to the projection of this surface is equal to the ratio of the intensity of light emitted in a given direction to the projection radiating surface(Fig. 4).

Rice. 4. Brightness

Both the luminous intensity and the projection of the emitting surface do not depend on distance. Therefore, brightness is also independent of distance.

Some practical examples:

Sun surface brightness - 2000000000 cd/m2

Brightness fluorescent lamps- from 5000 to 15000 cd/m2

Full moon surface brightness - 2500 cd/m2

Artificial lighting roads - 30 lux 2 cd/m2

Luminous flux is light energy emitted by a point source. Since it depends on the distance, it is expressed in spatial angles.

Lumen is a unit of measurement of the power of light radiation, which is estimated by the sensation of light to the human eye.

The unit of measurement for luminous flux, lumen, can be thought of as the total amount of light. For example, a 40 W incandescent lamp will create a luminous flux corresponding to 415 lumens, a fluorescent lamp will create a flux of 3200 lumens. Place any optical system around the light source, the amount of light (lumens) will be the same. Thus, if the number of lumens is not written on a non-directional light source, then it is not clear how it will illuminate.

Illumination and brightness

Illuminance is the amount of light, it quantifies light, which falls on a particular surface area of ​​the body. It depends on the wavelength of light, because the human eye perceives the brightness of different wavelengths of light differently, in other words, different colors.

Illuminance is calculated for different wavelengths separately. People perceive the brightest colors as:

• green - light with a wavelength of 550 nanometers;
• yellow orange. They are located next to it on the spectrum.

Light coming from red, blue and purple flowers, have a short or long wavelength, so they are perceived as darker. The concept of illumination is often correlated with the concept of brightness.

When lighting an area with the same lamp, a large area will be less illuminated than a small one.

Difference between brightness and illuminance

The Russian language gives two answers to the question of what brightness is. Brightness means a characteristic of luminous bodies, that is, a physical quantity. It also defines a subjective concept that depends on many factors, for example:

• structural features of human eyes;
• amount of light in the room.

The less light there is environment, the brighter the light source appears to us. You should distinguish between brightness and illumination and remember the following:

• brightness is the light that is reflected from the surface of a luminous object;
• Illuminance is the light that falls on the illuminated surface.

In astronomy, brightness includes two concepts, where stars emit and planets reflect. In this science, stellar brightness is measured on a photometric scale, and the greater brightness of the star is correlated with a smaller value. The most negative values ​​are bright stars.

The unit of luminance (candela per square meter) is used for applied or physiological purposes.

The lux unit is used to calculate light levels. One lux is equal to one lumen per square meter. The foot-candle is also used to measure illumination. She is consulted in the fields of cinema and photography and some others. The foot is in the name because the foot-candle means the candela illumination of a square foot of surface, measuring in one foot intervals.

Photometer

A photometer is a device that measures illumination. The light is sent to a photodetector, then converted into an electrical signal and measured. There are photometers that work on a different principle. Mostly photometers show light levels in lux, but there are also those who use other units. Those photometers, also called exposure meters, are involved in determining shutter speed and aperture, thereby helping photographers and cameramen. In addition, photometers are used to determine the level of safe illumination in other areas, for example, in crop production, in museums, where it is necessary to maintain the required illumination.

Safe flow of light at work

Working in a dark or dimly lit room can cause various health problems, be it blurred vision, depression or other physiological and psychological disorders. For this reason, in the workplace, as part of occupational safety regulations, minimum safe lighting requirements are included. IN final result The measurement produced by the photometer includes the area of ​​light propagation. These indicators ensure sufficient illumination of the entire room.

Light flux and museum exhibits

The speed at which museum exhibits will deteriorate and fade depends on the illumination and the intensity of the flow from the light source. Museum workers are working to determine the illumination of exhibits. This is done in order to ensure that there is a safe amount of luminous flux on museum units, as well as to ensure a sufficient level of illumination for visitors while viewing the exhibit.

The illumination level can be measured with a photometer, which is not easy to do because it should be installed as close to the exhibit as possible, and this requires removing the protective glass, turning off the alarm and obtaining permission. This task is made easier in another way, which is often used by museum staff. Instead of a photometer, a camera is used, which is not a replacement for a photometer in situations where more precise measurements found problem with lighting, but it is quite enough to identify a deviation from the norm.

You can determine the exposure with your camera based on the light level readings. The exposure illumination level is easy to determine using simple calculations. Museum staff resort to a formula or use a table, where exposure is represented in illuminance units. When making calculations, do not forget that the camera absorbs a certain amount of light, so you should take this into account.

Before providing a plant with the light it needs for photosynthesis, you need to know how much each crop needs. Gardeners and plant growers know this. They measure light levels to make sure each plant gets the amount of light it needs. Photometers are often used for such procedures.

Photometers are also widely used in laboratory practice. For example, a range of samples is determined with the help of which chemical composition. A special class of such devices includes a flame photometer. He detects alkali metals in samples, such as sodium, lithium, potassium. To detect them, you need to burn the sample at high temperature and use a photometer to analyze the flame spectrum. This problem is much more difficult to solve in other ways.

Modern photometers convert light radiation into electrical impulses; they are recorded using the principle of an ammeter and voltmeter, and then converted into a computer format.

A photometer is an instrument covering many fields of knowledge, such as chemistry, molecular biology, physics, materials science and others. The photometer is widely used in industry, laser and optical products. In addition to the chemical laboratory, the photometer finds application in forensic laboratories.

Thus, from the above, you have learned about the units of measurement of light, which It is better to buy lamps with the specified number of lumens that the concepts of illumination and brightness are different, but the amount of light can be measured special device.