Surface illumination is the quantity

∆Φ - luminous flux incident on the surface of the area

∆S, Figure 3.3. If ∆Φ = 1lm,

∆S = 1m, illumination = 1 lux, (lux).

That is, 1lx = 1lm: 1m2.

Figure 3.3

3.2.5 Law of illumination

Elementary transformations make it possible to establish the relationship between the surface illumination E and the distance R and the angle of incidence of light j on the surface, Figure 3.3, in the form:

Formula (3.9) is called law of illumination .

3.2.6 Luminosity of the emitting surface, m

So far, we have considered point light sources. Every real source has finite dimensions. Let a luminous area of ​​area DS, Figure 3.4, emit light into a hemisphere, which corresponds to a solid angle DW = 2πavg. Let us denote by DΦ PS the luminous flux emitted by the area DS into the hemisphere.

The value, lm/m2 is called Withdecency radiating areaDS.

According to Figure 3.4, luminosity M is numerically equal to the luminous flux emitted from a unit area of ​​the luminous surface into a solid angle of 2π steradians.

Figure 3.4

3.2.7 Brightness of the luminous surface, l

Let a luminous surface of area DS emits a luminous flux DΦ into a solid angle DΩ, the axis of symmetry of which makes an angle Θ with the normal to the emitting surface, Figure 3.5.

Figure 3.5

Magnitude

, (3.10)

according to , is called the brightness of the luminous surface.

3.2.8 Lambert's Law

In 1760, the German scientist Lambert showed that if the area DS not only emits light, but also ideally evenly scatters it in all directions, the brightness of the radiation L does not depend on the angle Θ included in (3.10).

According to Lambert's law

L L = const, (3.11)

for any Θ included in (3.10).

Elementary transformations, , show that for a Lambertian source, the relationship between the luminosity of the emitting surface M L and its brightness L L has the form:

M L = L L × π (3.12)

3.2.9 Light exposure, ns

Light exposure H C is the product of surface illumination E and time t during which the surface is irradiated. A-priory,

H C = E × t, (lx × s) (3.13)

At the end of Section 3.2, we present in Table 3.2 the main photometric characteristics, analytical expressions for them and dimensions in “S I“.

Table 3.2 List of main photometric characteristics.

Name of photometric quantities	Analytical expression	Dimension in “SI”
The power of light		Candela, (kd)
Light flow		Lumen, (lm)
Surface illumination		Lux, (lx), (lumen per square meter), (lm/m).
Luminosity of the emitting surface		Lumen per square meter (lm/m)
Luminous surface brightness		Candela per square meter, (cd/m)

3.3 Energy characteristics of optical radiation

3.3.1 Energy exposure, N E

A value equal to the ratio of the energy of radiation DW incident on a surface to the area of ​​this surface DS:

, (3.14)

3.3.2 Radiation flux, F E

A value equal to the ratio of the radiation energy DW transferred by radiation to the transfer time of this radiation Dt

F E = , (W), (3.15)

called radiation flux.

3.3.3 Energy luminosity Є (integrated emissivity)

The integral emissivity is equal to the ratio of the radiation flux F E to the area DS I from which this flux is emitted:

3.3.4 Surface irradiance, Є O

A value equal to the ratio of the radiation flux F E to the area DS P over which this flux falls and is absorbed

Bibliography

Ignatov A.N. Fundamentals of optoelectronics. Part 1. Emitting and photo-receiving devices. – Novosibirsk, 1988.

Ignatov A.N. Fundamentals of optoelectronics. Part 2.

Liquid crystal and electroluminescent indicator devices. – Novosibirsk, 1989.

Selivanov L.V. Fundamentals of optics. Part I. - Novosibirsk: SibGATI, 1995. – 54s

Selivanov L.V. Fundamentals of optics. Part II.

– Novosibirsk: SibGATI, 1995. – 56s.

Selivanov L.V. Fundamentals of optics. Part V. - Novosibirsk: SibGATI, 1997. – 56s.

Selivanov L.V. Fundamentals of optics. Part IV.

– Novosibirsk: SibGATI, 1997. – 63s.

Goss F., Hanchen H. Ann. Phys. Ser. 6, I. – Leipzig, 1947 – 333s.

Hansperger R. Integral optics. Translation from English. – M.: MIR, 1985. – 380s.

Mahlke G., Gessing P. Fiber optic cables. Translation from English. – Novosibirsk: PUBLISHER, 1997. – 264s.

Cheo P.K. Fiber optics. Translation from English. – M.: Energoatomizdat, 1988. – 279s.

Gower D. Optical communication systems. Translation from English. – M.: Radio and Communications, 1989. - With.

Mason U. Physical acoustics, vol. 3, part B. Translation from English. – M.: MIR, 1968. – 320s.

Lighting devices differ in design, physical properties and technical characteristics. The parameters of lighting devices raise many questions and disputes, especially the unit of illumination measurement. It is often confused with other concepts, such as luminous intensity or brightness. In addition, many consumers buy lighting fixtures based on the total value, without taking into account heat and light losses.

What is illumination

The concept of illumination is closely related to the magnitude luminous flux, measured in laboratories using special equipment. The illumination itself can be determined independently, and its value is taken into account by the relevant SNiPs. To calculate this parameter, use the luminous flux, measured in lumens, which is in relation to the area of ​​the illuminated surface. It should hit the surface at a 90 degree angle. Illumination is measured in special units - lux (lx).

The magnitude of the luminous flux has a direct impact on the physical and psychological condition person. Too little lighting depresses the brain, and too bright, on the contrary, has a stimulating effect on brain processes. Such a negative effect causes premature wear and tear of the body and has a detrimental effect on the organs of vision.

Therefore, when drawing up a lighting design and placement of lighting devices, a safety factor must be used that takes into account the likely drop in illumination during operation. Gradually, optical components wear out and become dirty, which leads to a decrease in the brightness of artificial light. In addition, the natural light factor decreases as the reflective properties of surrounding objects gradually change.

Illumination is primarily measured at the workplace. At the same time, sound vibrations are determined, the degree of contamination, electromagnetic and even gamma radiation are taken into account. The measurement results allow you to create the most optimal conditions labor, in accordance with sanitary standards and rules.

In what units is illumination measured?

The unit of illumination measurement should be discussed in more detail. The generally accepted unit is lux, which represents the illumination when a luminous flux of 1 lumen falls on a surface of 1 m2.

How much illumination does the unit of measurement 1 lux actually include? For this purpose, it is necessary to compare several standard parameters based on human physiology, enshrined in strict medical rules and government standards. Without compliance with them, it is impossible to approve any construction project.

An illumination level of 1 lux is created by an ordinary candle located at a distance of 1 m from the illuminated surface. With the help of this simple device it is quite possible to calibrate a homemade measuring device- lux meter.

As examples for comparison, we can take several known species illumination

• Bright sunlight at noon will be 100-140 thousand lux
• Sky without clouds during the day - 6200 lux
• Table lamp illuminating the table - 500 lux
• Illumination in the shade on a sunny day - 430 lux
• The onset of twilight in the evening - 70 lux
• The beginning of the night with moonlight - 1.5 lux.

Light sources and surfaces that reflect light do not always appear as individual points. If the visual organs are able to distinguish their shape, then we will talk about another photometric quantity known as brightness. Her physical properties similar to the intensity of light, however in in this case this relationship will not be absolute. It is proportional to the area of ​​the reflecting or radiating surface.

Brightness, as a physical concept, is the only photometric quantity that the human eye can normally perceive. It is clearly manifested in the properties of large light sources, consisting of a large number of point emitters. Provided they are of the same brightness, the overall light of a large lighting fixture will be perceived as a single whole.

List of basic units of measurement

There are several basic units of measurement that characterize the parameters of light in one way or another. Among them, the most famous and widespread are the following:

• Light flow. Represents the power of light emitted. This is the visible spectrum of radiation associated with the sensation of light perceived by the human eye. This value is measured in lumens (lm). For example, the luminous flux emitted by a 100-watt incandescent lamp is 1350 lm, and by a fluorescent lamp LB40 - 3200 lm.
• The power of light. The density of the luminous flux relative to the surrounding space. At its core, it is a proportion where the luminous flux is related to the solid angle within which the radiation is uniformly distributed. The unit of measurement is candela (cd).
• Illumination. The luminous flux incident on the surface has a surface density. It is evenly distributed and correlates with the area of ​​the illuminated surface. The unit of measurement is lux (lx), equal to 1 lm/1 m2.
• Brightness. Represents the luminous intensity with surface density in a specified direction. The unit of measurement is cd/m2.
• Luminosity. The luminous flux emitted by a surface with density, which is the ratio of the luminous flux to the area of ​​the luminous surface. The unit of measurement is 1 lm/m2.

Instruments for measuring light levels

The level of illumination is measured by a device - a lux meter. This small, portable device works in much the same way as a photometer. A stream of light radiation hits a semiconductor photosensitive element and begins to tear off electrons from it, which begin to move in an orderly manner. As a result, the electrical circuit closes. In this case, the magnitude of the current is proportional to the intensity of illumination of the photocell and is displayed on the scale of analog devices.

Currently, there are practically no instruments with arrows left; they have been replaced by digital measuring equipment. Each lux meter is equipped with a liquid crystal display and a photosensitive sensor located in a separate housing. A flexible wire is used to connect these two parts together.

Before starting light measurements, the lux meter is set to a horizontal position. Modern GOSTs require that different points in the room be used for measurements in accordance with established scheme. Natural and artificial lighting are measured separately. When performing the procedure, even the slightest shadow is not allowed to fall on the device. There should not be any sources of electromagnetic waves nearby. All these factors can cause interference and affect the measurement results.

The resulting illumination value must be compared with the parameter established by GOST. Based on these data, conclusions are drawn about the sufficient or insufficient illumination of any room or area. After the tests, an evaluation protocol is drawn up.

Lighting and LED fixtures

When illuminated by LEDs, it emits a large number of heat. To dissipate it, heat-conducting structures made of aluminum, cooling fins and other elements are used that neutralize the effects of heat. When creating new lamps, specialists must take into account the relationship between illumination and heat loss.

Operational difficulties appear when the temperature rises above 50 degrees. In this regard, measurements should be taken approximately two hours after the start of work. LED lamps. To eliminate errors, illumination measurements are performed periodically throughout the working day. It is recommended to conduct such studies at least once a year.

>>Illuminance

• Remember how you felt when you entered a dark room. You feel a little 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;
the sun's rays in bright room(near the window) - 100 lux;
on the street at 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 illumination, he can simply take a more powerful flashlight, since it is obvious that as the light intensity of the source 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 an increase in 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 illumination called? 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 up another 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.

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Often, lighting in a house or apartment is determined by a minimum of parameters. This is the lighting design and placement. And even knowing about illumination standards, many simply do not take them into account. This is certainly not a critical error. But if you select lighting according to the rules and standards of illumination, correctly calculate how much light is needed for a certain room in an apartment, you can achieve a stable psycho-emotional and physical state for a person.

How many lumens are needed for 1m2

An integral part of a comfortable stay at home or at work is lighting. Few people know that the right light helps relieve psychological stress or, on the contrary, concentrate on work. But before moving on to calculations, it is necessary to understand the measurement values. Lumen (Lm) is a unit of measurement of luminous flux, Lux (Lx) - the illumination of a surface is measured in lux. 1 lux is equal to 1 lumen per square meter.

Calculation (measurement) of lighting intensity is carried out using a simple formula (AxBxC) in which:

• A – required illumination according to SNiP standards;
• B – room area (sq. m);
• C – Height coefficient.

The height coefficient is a correction value and is calculated depending on the height of the ceiling. 2.5 and 2.7 – coefficient equal to one; if 2.7 and 3 meters - 1.2; ceilings with a height of 3 and 3.5 meters - 1.5; from 3.5 to 4.5 meters – coefficient is 2.

Table of illumination standards according to SNiP in lux (Lx):

For office premises	Norm (degree) of illumination	For residential premises	Illumination standards
Office using computers		Living rooms, kitchens
Drawing office
Meeting room		Bathroom
Ladder		Ladder
		Library
Utility rooms
		Wardrobe

We make a calculation. Suppose you need to find out the required amount of light for a children's room, the area of ​​which is 15 square meters, with a ceiling height of 2.7 m. For accuracy, we use a calculator. We multiply the amount of illumination by square meters and by the height coefficient - 200 x 15 x 1 = 3000. Accordingly, the luminous flux should be 3000 lumens (Lm).

Divide rooms of irregular shape into shapes (for example, a square and a triangle), and perform the calculation separately for each.

You can measure the level of illumination at home with a lux meter.

Living space lighting

Lighting in the house is as important as the interior. First of all, they divide the entire space into areas that differ not only in size, but also in functionality.

Namely:

1. Hallway– its location implies the absence natural light, so they create something artificial in the hallway. For this purpose, directional lighting devices with wide dispersion angles are used.
2. Living room (hall)- a room with many functions. Therefore, maximum functionality is achieved with lighting, combining general with spot lighting.
3. Kitchen- an area that has separate work areas, in which spot lighting is added to the general one.
4. Bedroom– intended directly for rest and sleep. For bedrooms, soft and warm tones of artificial light are selected. Also, it makes sense for them to adjust the lighting intensity.
5. Bathroom– as in previous cases, local lighting is added to the main one.

When choosing a lighting fixture for a bathroom, you need to make sure that this sample has a high degree of protection (IP) from humidity.

Proper lighting in the apartment will help not only emphasize or highlight a certain area, but also erase visual boundaries.

LED lamps for residential premises

Some time ago, LED lighting was considered unacceptable for the home. The main factors were the high price, as well as the brightness and color of the lighting.

But today, such lighting is becoming relatively inexpensive. And the choice in power, design, range and size is simply huge. The only limitation can be your imagination, where and how to use LED lamps. Also, such lamps have a number of advantages.

Advantages:

• Low energy consumption (allows long-term use to quickly recoup the cost of the lamp);
• Durability (if you choose a quality product, the service life is many times longer than that of conventional incandescent, fluorescent and halogen lamps);
• Does not heat up during operation (which increases the possibilities of placement in accordance with the design).

And these are not all indicators. The best option lighting, can be selected by spectrum and brightness (all values ​​are indicated on the product packaging). For your home, choose lamps that provide warm light.

When choosing LED lamps, pay attention to the manufacturer. The more famous the brand, the better the product.

An important factor is environmental friendliness. LED lamps do not emit UV radiation, and they do not create fluctuations in light output.

If you decide to do good lighting in the house, it is better to choose LED lamps for this.

Illumination standards for office premises: required value

It's not so common to find offices in which Special attention was given to lighting. Usually these are luminous squares with luminescent flickering, built into the ceiling. But light affects both the psychological and emotional state of a person. With proper lighting, you can achieve high employee productivity throughout the day.

The level of illumination in the office is determined by two standards:

• Russian – illumination level (required scale), recommended within 300 – 400 lux (Lx);
• International standard (European standards) – 500 lux (Lx).

Lighting is divided into general (direct and reflected), light from light sources is scattered throughout the entire office area, and local (lighting directly at the workplaces themselves), illumination is carried out by various lighting devices for local lighting (table lamps and lamps).

The placement of lighting fixtures parallel to the windows is the most correct; this ensures that the light from the lamps matches the light from the windows.

Important and individual approach for each workplace in the office, this is due to the difference in lighting needs for each employee. This is influenced by factors such as vision and age.

Children's playground lighting: standards

Modern playgrounds, of course, differ from sports ones, but in terms of their functionality they can be equated to each other. In addition to the usual slides, swings and carousels, many sports equipment are added for the physical development of children. Therefore, competent and effective lighting for children's playgrounds is simply necessary.

With these characteristics, for children playgrounds important parameters need to be taken into account.

List of parameters:

• Ensuring comfort and safety;
• Injury prevention;
• Possibility to be on site in the evening (especially in winter).

The lighting standard for children's playgrounds according to the Russian standard is 10 lux. But as sites are improved, the required (normal) level of illumination should be 70 - 100 lux.

The level of color rendering is of great importance when lighting children's playgrounds. For easy identification of small and moving objects.

In accordance with the dimensions, the optimal ratio of height and location of lighting fixtures is selected for various playgrounds. These include cantilever (up to 10 meters high) and local (up to 4 meters high). The power of a separate street lighting device is calculated according to SNiP standards.

If the site is not sufficiently illuminated, the lighting must be improved by adding lighting fixtures.

It is worth taking into account the aesthetic component by choosing lamps that highlight the exterior of the site.

How many watts are needed to light a room: converting lumens to watts

The questions - how to determine what lighting should be in a separate room or one room, how to convert lux into watts, how to select and calculate the required number of lamps - have fairly simple answers.

Let's do the calculation using an example. We need to illuminate a hall of 20 m2 with a chandelier with five incandescent light bulbs. What power in watts should I choose for lamps?

To calculate you will need:

• Illumination level;
• Area in square meters.

We multiply the illumination rate by square meters. 150 x 20 = 3000. The total luminous flux should be 3000 Lumens. This means that for normal lighting you will need 5 lamps of 60 watts each. If you convert to European standards, you get 4000 lumens.

Due to outdated standards, multiply the illumination standard by 1.5 times.

Do not forget, unlike incandescent lamps, there are several other types of artificial lighting sources that are more reliable and economical.

What are lighting standards (video)

The right light is needed not only at home or in the office. It is necessary for comfortable rest in a hotel, walking down the street, its use in kindergartens and shopping malls is important. The only difference is purpose and functionality. Based on the tests conducted, psychologists have proven that with well-designed lighting, not only the psycho-emotional, but also the general condition of a person improves.

It is difficult to meet a person who does not understand measures of length, area, volume, and weight. It is not difficult to calculate time or determine temperature. But if you ask someone about photometric quantities, then in most cases you cannot expect a clear answer. Meanwhile, we live in constant contact with lighting, natural or artificial. This means that we must learn to evaluate it in some way.

Of course, such an assessment is always made by everyone, but most often - purely at the level of subjective perception: is there enough light or not. However, such a “gradation” is precisely subjective and can produce significant errors. The consequences of such incorrect assessments cannot be underestimated - both insufficient lighting and its excess negatively affect both a person’s visual organs and his psycho-emotional state.

Meanwhile, there is a special value - illumination, the value of which is regulated by legislative acts in the field of construction and sanitation. That is, illumination is precisely the quality criterion that allows you to correctly evaluate the organization of a room lighting system. In this article we will talk about this parameter and other photometric quantities associated with it, and see how this can be used in a practical application.

Due to ingrained habit, many continue to believe that the assessment of room illumination can be done in energy units - watts. This misconception is easily explained - we are left with this persistent stereotype as a legacy from the times of complete dominance of incandescent lamps.

Incandescent lamps were produced with different power consumption - 15, 25, 40, 60, 75, 100, 150 and more watts. And every owner of a house or apartment knew from his own experience that for normal lighting in the living room, for example, he must screw three 60-watt bulbs into a chandelier, a “forty” will be enough for a table lamp, a hundred-watt one for the kitchen, etc.

By the way, a clear legacy of this is still the practice used by lamp manufacturers - to indicate on their packaging, in addition to power consumption, luminous efficiency expressed in the equivalent power of old incandescent lamps.

So let's remember the first thing - neither the luminous flux emitted by a lamp nor the surface illumination resulting from it is measured in watts. The watts indicated on the body of the device are the amount of electricity consumed by the lamp, which, through certain physical transformations, is converted into visible light.

Some people of the older generation are generally sure that the luminous output of a lighting device is measured in candles. By the way, this is not so far from the truth, and why will become clear below. But again, this is not illumination at all.

So it makes sense to consider the main photometric quantities in order, from the light source to the illuminated surface. Let’s make a reservation right away – this topic is quite difficult for an unprepared person to understand. Therefore, we will try to simplify the presentation as much as possible and will not overload it with cumbersome formulas. So that there is simply a general understanding of the issue.

Light flow

Light, as is known, has a wave nature. In a certain wavelength range electromagnetic radiation is perceived by the human visual organs, that is, it becomes visible. The approximate boundaries of this range are from 400÷450 nm (red part of the spectrum) to 630÷650 (violet region).

Electromagnetic waves are a carrier of energy - it is the energy of the Sun that provides life on Earth. But let's digress from astronomical categories and return to ordinary light sources.

So, since a source emits light, this means radiation and transfer of a certain energy. The amount of this radiant energy (We) transferred per unit time is called radiant flux (Fe). And it is measured in watts.

However, we are talking about lighting, that is, the perception of color by human vision. And estimating the amount of energy “by eye” means immediately introducing a large error. For example, two sources with equal radiation power, but with different colors glows will also be perceived by the eye differently.

To unify this parameter, a special physical quantity was introduced - luminous flux (F). This is also an indicator of the power of the radiant flux, but only that part of it that is perceived by the average healthy human eye.

Luminous flux can also be measured in watts (this is rather an energy indicator), or in lumens (light indicator). In practice, lumens are usually used.

For the exact value of one lumen, radiation from the central, green part of the visible spectrum, with a length of 555 nm, was taken as a standard.

So, it is accepted that a radiant flux with a wavelength of 555 nm and a value of 1 watt corresponds to 683 lumens. Why such a strange coefficient? It’s just that the final approval of this unit in the SI system took place in 1979, and the first experiments in photometry with the introduction of the luminous flux indicator began to be carried out long before that. At that time, when electric lighting did not yet exist, and an ordinary candle served as a more or less stable, “reference” light source. And the current ratio of energy watt and light lumen was recalculated over time and passed down to the present day.

Let us remind you once again that the watts mentioned above, which can also be used to measure the luminous flux, have nothing to do with those indicated on the lamp packaging. It shows the consumption of the lamp, that is, the amount of energy that it will “take” from the network. We should be more concerned about its energetic light output - how much visible radiant energy it will “give out”. So, when choosing a lamp, it would be much more correct to pay attention not to ephemeral comparative analogies in watts, but to the clearly indicated value of the luminous flux in lumens.

Luminous output

This is a very interesting quantity in practical terms, since it essentially characterizes the efficiency of the light source. It is important to choose a lamp not based on its electrical power consumption, but on how this power is used when converted into light energy.

So, the luminous output value shows how much luminous flux is produced by the lamp when converting one watt of expended energy. It is clear that it is measured in lumens per watt (lm/W).

The conversion of one type of energy into another is carried out in different ways. For example, in conventional incandescent lamps the resistive principle is used - the glow is caused by a red-hot coil with high electrical resistance. It is clear that this is accompanied by huge heat losses. More efficient are modern lighting devices based on the principles of glow of semiconductor matrices when current is passed or specially selected gas mixtures are ionized. Here, significantly less energy is wasted on unnecessary heating.

It was already mentioned above that the peak of normal perception of light by the human eye occurs at a wavelength of 555 nm. And in ideal conditions, with full transformation electrical energy in a monochromatic light flux of the specified wavelength, that is, with absolutely no losses, it is theoretically possible to achieve a light output of 683 lm/W. This is called an ideal light source, which, alas, does not exist in nature.

The table below shows comparative characteristics for the most commonly used lamps in everyday life - incandescent, fluorescent and LED. It is clearly visible how more economical the use of modern light sources becomes, that is, how the luminous efficiency increases.

(The values ​​in the table are approximate. In any category of lamps there may be deviations in one direction or another - this depends on the quality of the particular model. But the table presents the general picture quite clearly).

Luminous flux, Lm	Incandescent lamps		Fluorescent lamps		LED bulbs
	Consumed Power, W	Luminous output lm/W	Consumed Power, W	Luminous output lm/W	Consumed Power, W	Luminous output lm/W
250	20	12.5	5÷7	41.7	2÷3	100
400	40	10	10÷13	36.4	4÷5	88.9
700	60	11.7	15÷16	45.2	6÷10	87.5
900	75	12	18÷20	47.4	10÷12	81.8
1200	100	12	25÷30	43.6	12÷15	88.9
1800	150	12	40÷50	40	18÷20	94.7
2500	200	12.5	60÷80	38.5	25÷30	90.9

The specific luminous efficiency value is not always, but is still indicated by some lamp manufacturers on their packaging. This may be the inscription “light output” or “Lighting effect”. If not, then it’s easy to determine it yourself by dividing the nameplate luminous flux by the specified power consumption.

It is quite obvious that of all the lamps used in living conditions, have the best light output indicators LED devices– for them this figure reaches 100 lm/W, and may even be slightly higher. But progress does not stand still, and the developers announce an imminent release serial production lamps with a luminous efficiency of about 200 lm/W. But the ideal source is still oh so far away...

By the way, scientists were able to estimate the luminous efficiency of the Sun, and it is not so high: approximately 93 lm/W.

About the luminous efficiency of light sources various types This is also explained in the video below:

Video: What is luminous efficiency, and what is the practical application of this parameter?

The power of light

In physics there is the concept of a point source of light - it propagates radiation exactly the same in all directions. In practice, if this happens, it is extremely rare, and even then - with some simplification of concepts. In fact, the luminous flux in different directions is uneven. And in order to estimate, let’s say, its spatial density, they operate with the magnitude of the light intensity. And to understand what it is, you will also have to remember the concept of a solid angle.

Let's start with geometry. So, a solid angle is a part of space that unites all rays emanating from one point and intersecting a certain surface (it is called a contracting surface). In photometry, of course, this is an illuminated surface. This angle is measured in special quantities - steradians (sr), and is usually indicated in formulas by the symbol Ω .

The magnitude of the solid angle is the ratio of the area of ​​the subtending surface to the radius of the sphere.

Ω = S/R²

That is, if we take, for example, a sphere with a radius of one meter, then a solid angle of one steradian will “cut” a spot on its surface with an area of ​​one square meter.

Why know this? The fact is that the concept of luminous intensity is directly related to the solid angle. Specifically, a luminous flux of one lumen, propagating in a space limited by a solid angle of one steradian, has a luminous intensity of one candela. Mathematically, this relationship looks like this:

I = Ф/ Ω

And if we talk about the energy intensity of light equal to one candela, then this is 1/683 W/sr.

By the way, the candela is one of the seven basic quantities of the SI system.

Candela literally means candle in Latin. This is exactly that “relic of the past” that was already mentioned above, but it very clearly shows the entire interconnection of quantities.

Let's explain in the figure:

So, there is a point source of light - a candle. Its burning wick emits light with an intensity of one candela (item 1).

In a space limited by a solid angle equal to one steradian (item 2), a luminous flux (item 3) equal to one lumen will propagate. At a certain distance from the source (radius of the sphere - position 4), this flow illuminates the surface of a certain area (position 5). Looking ahead, we will immediately say that if the area is equal to one square meter, then under such conditions in this “light spot” an illumination equal to one lux (lx) is provided.

If we return to the candle as a reference light source, then it is easy to calculate its total luminous flux. A complete sphere has a solid angle of 4π, that is, with slight rounding, it is equal to 12.56 steradians. This means that a candle emitting light of one candela in all directions produces a total luminous flux of 12.56 lumens.

It is interesting that not so long ago the emissivity of light sources was assessed “in candles”. For example, they said that you need a “light bulb for sixty candles.” Sellers and buyers understood each other perfectly - a 60 W incandescent light bulb was purchased, although, in fact, these quantities are in no way related to each other in this case, from the point of view of physics. And what’s funny is that it was close to the truth.

Let's see - 60 candles of 12.56 lumens will give a total of 753.6 lumens. Let's look at the table above - an incandescent lamp with a consumption of 60 watts has a luminous flux of approximately 700 lumens. Very close!

But, we repeat, a correct assessment of light sources should still be carried out in lumens.

Light brightness

Another parameter worth considering is the brightness of the light source. The fact is that there is practically no need to deal with point sources. That is, most sources have some kind of specific radiating surface. And with an equal luminous flux, but a different area of ​​light emission, it will be perceived differently by vision.

That is, in essence, brightness is the strength of light emitted from a certain unit area of ​​the visible surface of a light source.

It is clear that the unit of brightness will be candela per square meter.

This is an important value, since the organs of vision, when looking at a light source, react, rather, not to the intensity of light as such, but rather to brightness. When its value is large (over 160 thousand candelas per square meter), the light can cause eye irritation, pain, and tearfulness. That's why lighting manufacturers produce lamps with frosted bulbs. With virtually no loss of luminous flux, the radiation does not come specifically from an incandescent filament or LED with their small areas, but from a much larger surface area of ​​the bulb. This glow is much safer for the retina of the eye and is perceived much more comfortably by vision.

Surface illumination

Finally, we got to the lighting. This value can be considered the most applied, since it is the illumination of a particular area that is assessed general work lighting fixtures.

Figuratively speaking, illumination (E) is the surface density of the luminous flux (F) distributed over a particular area (S). If we approach it with some simplification, then this can be expressed by the following formula:

As we saw above, one lumen of luminous flux on an area of ​​one square meter creates an illumination equal to one lux (lx).

Illumination depends on a number of factors, even if you do not take into account the own characteristics of the light source.

• Firstly, the further the source is located from the illuminated surface, the larger the area of ​​the “light spot” (remember the solid angle cone). That is, the luminous flux is distributed over larger area. Moreover, as we remember, this dependence is quadratic. That is, if the distance is doubled, the illumination will decrease four times, three times - nine times, etc.

If we consider a point source, we can apply Kepler’s formula:

We will not repeat the meaning of the quantities included in the formula - they are given above.

• Secondly, the Kepler formula shown above is valid only for a surface perpendicular to the direction of the light flux. In reality, of course, this does not happen often. That is, in the case when the illuminated plane is located at some angle α to the direction of the flow, corrections have to be made for this:

E = (I / r²) × cos α.

Remember - when you need to illuminate a surface as brightly as possible, you point the flashlight perpendicular to it. But if you place it at an angle, the illumination will drop sharply, since the light seems to be “smeared” across the surface.

• Thirdly, the illumination of a particular area also depends on its, so to speak, surroundings. The fact is that most surfaces do not absorb all the light that hits them, but largely reflect it. And thus they themselves become original sources of light.

Let's remember what was said in the section about the brightness of the glow. Yes, indeed, the brightness of such illuminated areas is not particularly high. But the radiation comes from a decent area, and as a result a very significant luminous flux is created.

And the brightness of such an illuminated surface depends both on its illumination and on its diffuse reflectivity, which has a separate name - albedo. The higher the albedo, the brighter the glow. And since it’s brighter, the “secondary” color flow is more studied.

Some illustrative examples reflected light. A sheet of white paper with illumination of only 50 lux will have a brightness of 15 cd/m². The glow of the full moon (and this, as we know, is sunlight reflected from its surface) is characterized by a brightness of 2500 cd/m². And the surface of pure white snow on a sunny day reaches a brightness of up to 3000 cd/m². Quite a lot!

This phenomenon is very widely used in lighting and design rooms. Entire model lines of lamps are produced that are specially designed to be directed towards walls or ceilings, that is, it is the illuminated areas that are included in the work of general lighting of the room. The same effect is used when creating multi-tiered ceiling structures with LED strip lighting.

It is easy to guess that the illumination of the room will depend on the chosen style of its decoration. The same light bulb, say, in a white room will provide much greater illumination than in one painted in dark colors.

Since the final expected result of the operation of lighting devices is the creation of comfortable and healthy lighting levels in the room, it is the value of surface illumination that is subject to regulation. Legislative acts (SNiP and SanPiN) indicate what illumination should be achieved in various rooms, depending on their purpose.

Thus, the current SNiP 23-05-95 in its updated version (Code of Rules SP 52.13330.2011) specifies the following standard illumination indicators for residential buildings:

Type (purpose) of the premises	Illumination standards in accordance with current SNiP, luxury
Living rooms	150
Children's rooms	200
Office, workshop or library	300
Cabinet for precision drawing work	500
Kitchen	150
Shower room, separate or combined bathroom, bathroom	50
Sauna, locker room, swimming pool	100
Entrance hall, corridor, hall	50
Entrance lobby	30
Stairs and landings	20
Wardrobe	75
Sports (gym) room	150
Billiard room	300
Storage room for strollers or bicycles	30
Technical rooms – boiler room, pump room, electrical control room, etc.	20
Auxiliary passages, including in attics and basements	20
Area at the main entrance to the house (porch)	6
Area at the emergency or technical entrance	4
Pedestrian path at the entrance to the house for 4 meters	4

In this case, the assessment of illumination should be carried out on a horizontal plane at floor height. For stairs - both at floor height and on transition platforms and steps.

To assess the level of illumination, they are used special devices– lux meters. They consist of a photodetector with a spherical sensor surface, and a converter unit with an analog (arrow) or digital indication of readings.

It is clear that a lux meter is a highly professional, expensive device that is used by specialists, and which is absolutely not required to have at home. But understanding the basic photometric quantities will not hurt any owner of a house or apartment.

For what? - many may ask. Yes, at least in order to be able to independently plan the use of certain light sources in order to achieve required illumination. After all, the health and general mood of all family members directly depends on it.

The practical position of this knowledge will be discussed in the next section of the publication.

Colorful temperature

To finish the conversation about the main characteristics of light sources, it is necessary to dwell on their color temperature.

With completely equal indicators of the emitted luminous flux, one light bulb can give a warm yellowish color, another - a neutral white, and a third, for example, can glow with a cold shade of blue. How to distinguish them by this parameter? A special color temperature scale has been developed for this purpose.

Let's make a reservation right away - there is no connection between the air temperature in the room or the heating temperature of the light source itself. The glow of a physical body heated to high temperatures is simply taken as a standard.

Any body, if its temperature is above absolute zero, is itself a source infrared radiation. As the temperature rises, the wavelength of this radiation changes, and at a certain moment it reaches the visible part of the spectrum.

Probably everyone has observed this - when heated, a metal rod first turns red, then begins to glow with a bright red light; you can heat it, as they say, “white-hot.” And when performing electric welding work, when the arc temperature reaches very high levels, the melting metal can acquire a blue tint.

It is this gradation that forms the basis of the color temperature scale. It is indicated in Kelvin - and on the scale you can see what kind of glow the lamp will emit.

This color temperature is usually indicated in the lamp labeling. Sometimes it is accompanied by a text explanation, or even a miniature scale showing in which region of the visible spectrum the lamp will glow.

The choice of lamps based on their color temperature depends on what kind of environment you plan to maintain in the room. Of course, a subjective factor will also play a significant role here - that is, the preferences of the owners. And there are no ready-made “recipes” for this. But the table below provides a recommended overview of lamps based on their glow. Perhaps this will help someone when choosing.

Colorful temperature	Visual perception	Possible definitions of the created atmosphere	Typical Applications
2700 K	Warm light	Open, warm, friendly, cozy, relaxing	Living rooms, hotel lobbies, small boutiques, restaurants, cafes
3000 K	White light	Intimate, friendly, conducive to communication	Living rooms, libraries, shops, offices
3700 K	Neutral light	Friendly, conducive to communication, giving a feeling of security, increasing attentiveness	Museums and exhibition halls, bookstores, offices
4100 K	Cold light	Focus-promoting, clean, clear, productive	Training premises, design bureaus, offices, Bolgitsy, large stores, train stations
5000 - 6500 K	Cold daylight	Disturbing, overly bright, emphasizing colors, sterile, tiring over time	Museums, jewelry stores, some offices in medical institutions

Carrying out independent calculations.

As promised, this section of the publication will discuss the algorithm for calculating illumination. More precisely, to be more correct, the calculation has just the opposite direction. That is, we already know the normal illumination value. And calculations should lead us to the result of how many lamps and with what luminous flux will be required to provide it.

General formula for calculations

So, let's start with the formula that will serve as the basis for our calculations.

Fl = (En × Sp × k × q) / (Nc × n × η)

Fl- this is the luminous flux of the lamp that needs to be installed in the lamp. That is, this is the very value that is the purpose of the calculations.

Yong- standard illumination of surfaces, depending on the type of room. It corresponds to the parameters established by SNiP and given above in the table. That is, we start from the standard value.

Sp- area of ​​the illuminated surface. Usually the area of ​​the room appears here if calculated general lighting. But if the goal is to calculate the illumination of a local area (for example, working area), then it is the area of ​​this zone that is substituted.

k- correction factor, which is often called the safety factor. Its introduction takes into account several circumstances affecting the luminous efficiency of lamps. Firstly, over time, many lamps begin to waste their emitting potential, simply put, to dim. Secondly, the emissivity can also be influenced by some external factors– this is the dustiness of the room or, say, a high concentration of steam, which prevents the free propagation of light rays.

If we are talking about residential premises, where dense steam should not exist, and dust is removed by regular cleaning, then the second group of factors can be discounted. And for the gradual loss of emissivity, the coefficient for different types lamps can be adopted as follows:

Fluorescent lamps (gas discharge): 1.2;

Conventional incandescent and halogen lamps: 1.1;

LED lamps: 1.0.

q- a coefficient that takes into account the uneven glow of certain types of lamps. It is taken equal to:

For incandescent and gas discharge lamps mercury lamps: 1.2;

For compact fluorescent lamps incandescent and LED light sources: 1.1.

Let's move on to the denominator of the fraction.

Nc- the number of lighting fixtures planned for installation in the room or in a separate area for which the calculation is being carried out.

n- the number of horns in the lamp planned for installation.

It is probably clear that the product of the last two values ​​shows how many lamps are planned for installation. For example, one five-arm chandelier is installed. Then Nc=1, and n=5. Or you plan to illuminate the room with two devices, each with three light bulbs: Nc=2, a n=3, But if the lighting is provided by one device with one lamp, both of these quantities will be equal to one.

η - luminous flux utilization factor. This correction value takes into account many factors relating to both the characteristics of the room and the specifics of the lighting fixtures planned for installation.

Since it is precisely this coefficient that remains an unknown quantity, calculations should begin with it.

Finding the luminous flux utilization factor

This value can be called a tabular empirical value. It depends on the area of ​​the room, and on the location of the lamp, and on the main direction of the light flux, and on the finishing of the flux surfaces, walls and floors.

First of all, to enter the table you will have to define the so-called premises index. It takes into account the dimensions of the room, moreover, precisely in the ratio of length and width, since in square room and in an elongated rectangular shape the light flux will still spread differently. And secondly, it takes into account the height of the lamp above the illuminated surface. As we remember, according to SNiP requirements, illumination is assessed on a horizontal plane at floor level.

Important - sometimes the height of the ceiling in a room is confused with the installation height of the lamp. But this is still not the same thing! For example, lighting fixture can be mounted on the wall (sconce), installed on a stand or placed on a table or bedside table (floor lamp or desk lamp), suspended from the flow at a certain distance from ceiling surface(chandelier).

The formula probably won't tell you anything. It’s better to suggest using an online calculator to determine this room index.