In what units is illumination measured - a list of basic ones

What is illumination

Illumination refers to the luminous value, which is defined as the ratio of the luminous flux to the area of ​​its distribution. This indicator is directly proportional to the light intensity of the source from which it comes. As it moves away from the surface, the illumination decreases. This dependence is inversely proportional to the square of the distance (inverse square law).

The illumination formula looks like this: E=(I*cos)/r2. I is the luminous intensity in candelas, r shows the distance from the light source to the surface. This concept should not be confused with the brightness of light.

Mathematical definitions

Illumination

Surface illuminance, designated E

e ("e" means "vigorous" so as not to be confused with photometric quantity), is defined as[2
] mathrm {e}}} { partial A}},}
where

• ∂ is the partial derivative symbol;
• Φreceived radiant flux;
• And
  this is the area.

If we want to talk about the radiant flux emitted

superficially, we're talking about a shining exit.

Spectral illumination

Spectral irradiance at surface frequency, denoted E

e, ν, is defined as[2]
E e, ν = ∂ E e ∂ ν, { displaystyle E_{ mathrm {e}, nu} = { frac { partial E_{ mathrm {e} }} { partial nu} },}
where ν

this is the frequency.

Spectral irradiance at surface wavelength, denoted E

e, λ, is defined as[2]
E e, λ = ∂ E e ∂ λ, { displaystyle E_{ mathrm {e}, lambda} = { frac { partial E_{ mathrm {e} }} { partial lambda} },}
where λ

this is the wavelength.

In what units is illumination measured?

The unit of illumination measurement is not one indicator; there are several main options adopted in different measurement systems. For applied use there is no need to understand complex algorithms and formulas. It is enough to study the features of each unit and use it correctly, if necessary.

Lighting may vary at different points in the room.

Candela

In a measurement system, one of the seven basic units that are fundamental. This is the luminous intensity emitted by a monochromatic radiation source with a frequency of 540x1012 Hz . Moreover, the luminous flux must propagate in a given direction subject to a number of additional conditions.

The frequency that is used as a reference corresponds to the green part of the spectrum, since it is best perceived by human vision. When using a light source with a different frequency, greater intensity will be required to achieve the desired value.

1 candela is the light coming from a candle.

Not so long ago, candela was defined differently. It corresponded to the intensity of light emanating from a black source heated to a temperature of 2042.5 K (melting platinum), which was perpendicular to the plane and spread over an area of ​​1/60 square centimeter. This quantity is used in astronomy and many other sciences.

By the way! The coefficient 1/683 used by modern scientists is selected so that the new and old definitions correspond to each other.

Translated from Latin, “candela” means candle. It is believed that the light emitted by one candle is equal to 1 candela.

Lumen

Used in a system for measuring physical quantities and reflects the characteristics of lighting. 1 lumen is the luminous flux emitted by a light source with an intensity of 1 candela. To make it easier to understand, it’s worth considering simple examples:

1. Standard incandescent lamps with a power of 100 watts have a luminous flux of 1200-1300 lumens.
2. A fluorescent light source with a power of 26 watts provides a luminous flux of 1600 lm.
3. If we take the sun as a sample, then its luminous flux will be 3.63x1028 lumens.

Light also differs in temperature, this is also important to remember.

Lumen shows the total luminous flux that comes from a particular source. But it does not take into account important features - the presence of a lens or reflector, which can concentrate light in a small area and thereby significantly improve illumination. Different lanterns with the same lamp can illuminate either 10 or 100 square meters. In fact, this is all the light that the lamp gives, including that which does not fall on a given surface and is useless.

Keep in mind that a 1500 lm in a lamp with a reflector will provide better conditions than the same option in a diffuser lamp.

If the power exceeds the standard range, special indicators are used:

1. Multiple lumen units are generated if the value is an integer number of times greater than the set value. They are usually denoted as powers of a number. For the name, established prefixes are used that reflect the magnitude of the value.
2. On the contrary, lumen subunits are smaller than the established unit by an integer number of times. Special prefixes are also used here, and the degree is indicated with a minus sign.

Lux

This unit is the most useful, since it is with its help that the illumination in living and working spaces is measured. It is equal to a luminous flux of 1 lumen distributed over an area of ​​1 square meter. The indicator is used to regulate various standards and control lighting where required.

For simplicity, we can look at two examples. If a lamp with a power of 100 lumens is directed onto an area of ​​​​a square meter, then the illumination will be 100 lux. And if the same light source is distributed over 10 square meters, then the indicator will be 10 lux.

The video talks about luminous flux and illumination (how they differ, how they are measured)

Lumen and Watt

When only incandescent lamps were sold, watts were used as a guide to determine the lumen output of a lamp. Everyone knew that the more power, the higher the brightness of the light. But with the advent of other types of light bulbs, this characteristic has lost its relevance, since it cannot be used in determining equipment performance. Different options have different ratios of power in watts to luminous flux, so you need to understand the main types of equipment:

1. For incandescent lamps, the standard is 1300 lm at a power of 100 watts. For 40 W models, the luminous flux will be 400 lumens, and for 60 W – 800. And remember that over time, the brightness inevitably drops due to the thinning of the filament, so when calculating, it is worth including a certain margin.
2. Mercury arc lamps have a ratio of 58 lm per watt, the power is simply multiplied by this figure.
3. Fluorescent light sources have a ratio of 60 lm per watt.
4. There is no clear standard for LED lamps with a frosted diffuser, since the characteristics of the bulb and its light transmittance may vary. Typically the indicator varies from 80 to 90 lm.
5. Filament (clear) LED bulbs have a ratio of 100 lumens per watt of power.

The ratio of power and luminous flux differs for different types of lamps.

Actual performance may differ from generally accepted values ​​if the lamp design has features that affect the quality of light.

Basic lighting concepts and their practical application

In nature, there are many electromagnetic waves with different parameters: x-rays, γ-rays, microwave radiation, etc. (see Fig. 1). The nature of all electromagnetic waves is the same; they differ only in wavelength (or frequency). Of all this variety, the human eye perceives only a narrow range of waves in the range from 380 nm to 780 nm, causing visual sensations. Electromagnetic radiation concentrated in this range is called light

. Thanks to light, we are able to receive information about the world around us through vision.

Rice. 1 Variety of electromagnetic waves

The sensitivity of the eye to radiation at different wavelengths of the visible range is not the same and is characterized by the so-called curve of relative spectral luminous efficiency of radiation

(see Fig. 2).

Rice. 2. Relative spectral luminous efficiency curve

The maximum of the curve lies in the yellow-green region of the spectrum and falls at a wavelength of 555 nm. This means that the eye is most sensitive to radiation at this wavelength. To assess the quantitative and qualitative parameters of light, a system of light quantities and units has been introduced, which is built on the basis of the relative spectral luminous efficiency curve of radiation, i.e., in essence, on the sensitivity of the eye to radiation at different wavelengths. Let us consider the main quantities of this system and what significance they have in practical lighting engineering. To begin with, let's focus on the parameters related primarily to light sources and lighting devices. These are quantities such as luminous flux, luminous intensity and luminous intensity curve, efficiency, luminous efficiency, color temperature, color rendering index, luminous flux pulsation coefficient. The total amount of light that is emitted by a light source is called luminous flux

(measured in lumens - lm).
In other words, it is the power of radiation in the visible range, estimated by its effect on the eye. In practice, light sources are used as part of a lighting device (lamp). In this case, the luminous flux at the output of the lamp is lower than that of an independent light source. The reason for this is losses in the optical system of the lamp. Therefore, they talk about the coefficient of performance - efficiency
, which shows the ratio of the luminous flux of the lamp to the luminous flux of the light source. Efficiency is the most important indicator of the efficiency of a luminaire's optical system. In practice, luminous flux is one of the main parameters, and manufacturers of light sources must provide it in their catalogs and information materials. However, it is often more important for the consumer to know the flow of the “lighting device + light source” system, but here the situation with indicating this parameter is not so clear. It is necessary to distinguish between two directions of development of lighting technology: traditional lamp devices and LED devices. For traditional lamps, the luminous flux is not given, since this approach is incorrect. This is due to the fact that the lamp in such a lamp is a replaceable element and is not part of it. Lamps with different luminous fluxes can be used in the same luminaire. This leads to the fact that the luminous flux of the lamp may vary depending on which lamp is used in it. Therefore, manufacturers of traditional lamps provide efficiency in their catalogs (see Fig. 3). Knowing the lamp flux and efficiency, it is not difficult to determine the lamp flux.

Rice. 3 Technical parameters of traditional street lighting devices using the example of data given in the GALAD luminaire catalog

In LED devices, LEDs are integrated into the design at the production stage and are their permanent part, so nothing prevents the luminous flux of the lamp from being presented in information materials (see Fig. 4).

Rice. 4 Technical parameters of LED street lighting devices based on the example of data given in the GALAD luminaire catalog

An interesting situation has developed in the market regarding the efficiency of LED lamps. It is conventionally assumed to be 100%, although in fact this is not the case. Since some portion of the light from LEDs is lost in any case: when passing through the protective glass, on the secondary optics, there may be other factors determined by the design features of the device. If a manufacturer insists that the efficiency of its lamps is actually close to 100%, you should be wary, because in most cases this is not the case. In light of the above, a reasonable question arises: if the efficiency of lamps is always less than 100%, then why do we need a lighting device at all? Why not use light sources yourself and get more light? The fact is that one of the main functions of a lighting device is the redistribution of the light flux from the light source in space. The distribution of luminous flux in space is characterized by intensity curve -
KSS
.
In everyday language, the luminous intensity curve shows in which direction the light is more intense and in which direction it is less intense. And the concept of luminous intensity
can be explained as a flow in a given direction.
Luminous intensity is measured in candelas - cd. Strictly speaking, the flow distribution in space is determined by a 3-dimensional photometric body
, and the CSS is a section of the photometric body by a certain plane (see Fig. 5).

Rice. 5. Type of photometric body and KSS, typical for road lighting fixtures

The light of the lamp spreads more or less evenly in all directions, and in most tasks it is necessary that the light falls on a specific plane. The light that does not fall on this plane turns out to be useless. Therefore, to maximize the concentration of light in the right place, a special light distribution is required, which is ensured by the reflector of the light device. For example, for road lighting, the KSS type shown in Fig. works most efficiently. higher. In the case of LED lamps, the situation is similar, only the light is redistributed due to secondary optics (see Fig. 6). Thus, it turns out to be more profitable to use a light source as part of a lamp, losing luminous flux, but gaining a more efficient distribution. The KSS of a lamp is one of its main characteristics, which often determines the feasibility of using the device for illuminating a given type of object.

Rice. 6. Formation of KSS using the example of lamp and LED street lighting fixtures

To assess the feasibility of using a particular lamp, it is equally important to know how efficiently electricity is consumed during its operation. In lighting technology there is a parameter called luminous efficiency

.
This is the ratio of luminous flux to power consumption, i.e., in other words, how many lumens are obtained from 1 W of electricity consumed. This parameter is directly related to light sources, because the process of converting electricity into light occurs precisely in the source. A lamp does not have such a function, so the application of this term to a lamp was considered incorrect for some time. However, in practice, it is important for the consumer to compare how much more efficient one lamp is than another in terms of energy consumption. Therefore, recently the concept of “light output of a lamp” has taken root in practice. Lamps and light sources compete not only in terms of the quantity of light, but also in its quality. Objective indicators of light quality are: color rendering index, color temperature and luminous flux pulsation coefficient. The color rendering index
(Ra or CRI) shows how well a light source reproduces the colors of objects compared to reference light sources.
The reference light source is, for example, sunlight. Our eye sees objects because the light reflected from them reaches our eyes. Therefore, the perception of these objects depends on their lighting (see Fig. 7). You can see with the naked eye that when objects are illuminated with different types of lamps, the color rendering will differ significantly. The maximum Ra value for reference light sources is assumed to be 100. Color temperature
(measured in Kelvin, K) in practical terms means the shade of white light that the source emits. Color temperature 2500 - 3500K corresponds to a warm shade of white light, 3500 -4500K - a neutral shade, 4500 - 6000 K - cold.

Rice. 7. Illuminating an object with different types of light sources

Light flux pulsation coefficient

shows how noticeable the flickering of the lamp lamp will be. For gas-discharge light sources operating with electromagnetic ballasts, the magnitude of the luminous flux changes with double the frequency of the current. In Russia, the frequency of alternating current in the network is 50 Hz, therefore, the luminous flux of the lamps pulsates at a frequency of 100 times per second (see Fig. 8). Electronic ballast ensures that the lamps operate at higher frequencies and minimizes the ripple factor. LEDs can also have flux ripple, which is determined by the parameters of their power supply. The eye does not perceive such flickering, but it can affect fatigue not only of the eyes, but of the entire human body.

Rice. 8. Pulsation of the luminous flux of discharge lamps operating with electromagnetic ballasts

These light quality parameters are most important to consider in indoor lighting. For example, for offices and trading floors, SP52.13330.2011 regulates the value of Ra to be at least 80. For streets and roads, this indicator is not set because it is not significant. The thing is that completely different visual work takes place in offices and on the street. In offices, it is necessary to clearly distinguish small details and colors of objects, and the quality of light is important for this. On the streets, it is enough to distinguish large objects in order to navigate in space, and this does not require high quality light. For example, street lighting is common with high-pressure sodium lamps, the color rendering index of which is Ra = 20, and objectively this is quite sufficient (see Fig. 9).

Rice. 9. Highway lighting, made on the basis of luminaires with high-pressure sodium lamps GALAD ZHKU15 Sirius. High pressure sodium lamps produce white light with a characteristic orange tint with Ra = 20

Let's consider other lighting concepts that apply to illuminated surfaces. These include: illumination, brightness, uniform distribution of brightness and illumination. Illumination

- this is the amount of luminous flux per unit area of ​​the illuminated surface.
The unit of measurement is lux (lx). Essentially, illuminance characterizes the amount of light on a surface. To understand which illumination value is high and which is low, the following typical examples can be given: - illumination from the full Moon on the surface of the Earth in winter at the latitude of Moscow does not exceed 0.5 lux; — direct illumination from the Sun on a summer day at the latitude of Moscow can reach more than 10,000 lux; — standardized illumination on the desktop in the office is 400 - 500 lux; - normalized illumination on roads is 6 - 30 lux. Surface brightness
. Further, the physical definition of brightness is not given, but only the essence of this parameter is explained in non-scientific language. The amount of light on the surface is determined by the illumination. However, the eye sees an object not due to the fallen object, but due to the light reflected from it. Light falling on a surface can be reflected in different ways: firstly, it can be reflected stronger or weaker, which depends on the properties of the material, and secondly, it can be reflected in different directions with different intensities. Therefore, the concept of brightness was introduced, which represents the amount of light entering the observer’s eye from a unit area of ​​the illuminated surface. The human eye reacts specifically to brightness. Units of measurement are cd/m2. In cases where the material of an object reflects light unevenly in different directions, the brightness depends on the direction in which the object is viewed. In such cases, illumination and brightness are not directly related. If we take a sheet of ordinary matte paper, then no matter what angle we look at it, it seems equally light, since its brightness is the same in all directions. But if we take a polished metal surface, in which almost all the incident light is reflected in one direction, we will notice that when viewed from different angles, its brightness changes (see Fig. 10).

Rice. 10. An example of objects with different reflective properties. On the left - the brightness of the object does not depend on the direction of view of the object, on the right - the brightness of the object depends on the direction of view

In Russian standards for lighting objects, the main regulated value is the illumination of the working surface indoors and outdoors. Although the eye, as noted, reacts not to illumination, but to brightness, it is illumination that is normalized, since it is much simpler to calculate and measure. However, the basis for standardizing road lighting is brightness. This is due to the fact that for modern road surfaces, brightness largely depends on the angle of incidence, and there is no direct relationship between brightness and illumination, which does not allow standardization by illumination. The standards also limit the glare created by the lighting installation, i.e., visual discomfort that occurs when there are bright sources in the field of view. This is a characteristic of lighting quality. For public buildings, for these purposes, a discomfort indicator M is introduced, in industry - a glare indicator P, in roads - a threshold brightness increment coefficient TI. The glare of a lighting installation can not only cause discomfort, but also reduce the contrast of the object with the background, reducing the visibility of objects. The glare effect of a lighting installation depends on many factors, among which the main ones are: the location of the lamps relative to the line of sight and their type. How much glare a lamp will have is largely determined by its design features. Has it been established that in the case of road lighting, the glare effect depends on the luminous intensity values ​​in the corner area? 75?, which in turn is determined by the optical system of the lamp (see Fig. 11). Therefore, this part of the CSS should be limited. At the same time, the brightness of the roadway is largely determined by the shape of the SRL in the angle range 0 - 80?. Therefore, to create a truly effective CSS for road lighting is not an easy engineering task. The manufacturer of GALAD lamps (View catalog), understanding the exceptional importance of this approach, traditionally, when developing lamps, pays special attention to the optical system, because the efficiency of the lamp's CSS depends on it.

Rice. 11. Characteristic KSS of a lamp for road lighting

As for lamps for interior lighting, recently the trend of using LED lamps in this area has become increasingly pronounced. This approach is justified from the point of view of energy efficiency, however, many lamps on the market have high overall brightness (this is the brightness of the visible luminous surface of the lamp). This is due to the fact that LEDs are very bright light sources, and sometimes even with matte diffusers it is not possible to reduce this indicator to an acceptable level. And the use of special optics is impractical from the point of view of the cost of the lamp. Often, measures to reduce overall brightness by using materials that diffuse light well also lead to a significant reduction in the luminous output of the device, so it is important to maintain a balance here. The manufacturer of GALAD lamps solves this issue by equipping the lamps with a large number of LEDs of lower power (and, accordingly, low brightness). This makes it possible to obtain a low overall brightness of the lamp and a very high uniformity of brightness of the luminous surface, which distinguishes these models from conventional LED lamps. In Fig. 12 on the left is a device with an unevenly bright surface and a higher overall brightness, on the right is the GALAD Cairo premio lamp, characterized by a higher brightness uniformity and a lower overall brightness value. In terms of appearance, the lamp on the left is more suitable for technical rooms, while the lamp on the right is more suitable for classic office lighting.

Rice. 12. Lamps with different uniformity of brightness of the luminous surface

So, we have looked at the main lighting parameters. The main goal that we pursued in preparing the article is to describe their meaning in simple and understandable language, as well as explain their practical significance. We hope that the article will be useful to those who are starting their activities in the field of lighting technology.

How to convert one unit of illumination to another

Previously, complex formulas were used to carry out calculations, but now this is no longer necessary. The most important thing is to have the value in a certain light unit on hand so that you can use the original data.

Next, you just need to find any illumination converter. The values ​​that are available are entered (the appropriate item is selected), and in the second column the illumination units to which they need to be converted are set. Calculations take a matter of seconds and are highly accurate, as they are made based on proven formulas.

Illumination scale in lux

To determine the appropriate lighting mode, you can use another option - the illumination scale. It sets recommended values ​​depending on the activity being performed.

The higher the accuracy requirements, the brighter the light must be.

One room may have several different zones if this is required for the normal performance of work.

How to determine illumination

When there is insufficient lighting, a person gets tired much faster, and he has to constantly strain his eyesight, which is extremely undesirable. Therefore, SNiP establishes standards for the main types of premises, which should be followed when determining the required illumination.

Light levels are set for all types of premises.

Natural light is taken into account, but the main attention is paid to artificial light, since with its help you can create optimal conditions regardless of the weather outside. Below are the main values ​​for different rooms:

1. Offices where people work on computers and prepare documents – 300 LK.
2. Premises for drawing work - 500 Lux.
3. Conference rooms, meeting rooms – 200 Lx.
4. Living rooms and kitchens – 150 Lk.
5. Children – 200 Lux.
6. Workrooms or areas – 300 Lux.
7. Classrooms and auditoriums – 400 Lx.
8. Trading floors – from 200 to 400 Lux, depending on the specifics.

There are special standards for work areas, so additional lamps are most often used there, which highlight a small part of the space.

As for determining illumination, a device called a lux meter is used for this. With its help, measurements are taken at several points in the room, they are indicated in SNiP, it is important to do everything correctly. Not only the general indicator can be checked, but also the illumination of a certain surface or equipment if it is necessary to provide special conditions when performing work.

Related video: How to measure the level of illumination in a room using a smartphone.

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 GOST standards require that different points of the room be used for measurements in accordance with the 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.

Features of determining illumination for LED devices

This type of equipment is the most popular, so you need to use several recommendations when choosing equipment and its operation. Once the required indicators have been determined, you should select specific light bulbs or lamps and calculate the quantity required for the room. It is important to distribute them evenly so that there are no poorly lit areas.

Measurements should be taken after the equipment has been operating for at least 2 hours. This is because the diodes get hot, which affects their performance. It is necessary to repeat measurements where it is important 1-2 times a year. Over time, the performance of diodes, especially low-quality ones, can greatly decrease.

By the way! LED lamps always have an indication of the luminous flux power, which simplifies the choice.

Understanding the units of illumination measurement is not difficult, since there are few options. And for practical use, just one is enough, so the easiest way is to choose a suitable measurement system and use it.

The difference between illumination and luminous flux

At the same time, many people confuse the units of measurement Lumens with Luxes. Remember, illumination is measured in lux.

How can you clearly explain their difference? Imagine the pressure and force. With just a small needle and a little force, high specific pressure can be created at a single point.

Also, with the help of a weak luminous flux, it is possible to create high illumination in a single area of ​​the surface.

1 Lux is when 1 Lumen falls on 1 m2 of illuminated area.

Let's say you have a certain lamp with a luminous flux of 1000 lm. Below this lamp is a table.

There must be a certain level of illumination on the surface of this table so that you can work comfortably. The primary source for illumination standards is the requirements of the codes of practice SP 52.13330

For a typical workplace this is 350 Lux. For a place where precise small work is carried out - 500 Lux.

This illumination will depend on many parameters. For example, from the distance to the light source.

From foreign objects nearby. If the table is located near a white wall, then there will be more suites than from a dark one. The reflection will definitely affect the overall outcome.

Any illumination can be measured. If you do not have special lux meters, use the programs in modern smartphones.

However, be prepared for errors in advance. But in order to do an initial analysis offhand, a phone will do just fine.

Minimum illumination in lux

If the lamp power is indicated in watts, it is necessary to convert the indicators into lux, since the standards are indicated specifically for them. There is information about how many lux are in 1 W of different light sources, so making calculations is not difficult. As for the minimum illumination, the data specified in SNiP are precisely the lower indicator that you should focus on.

The light can be brighter than the established standards; there are no special restrictions on this matter. The main thing is that there is no discomfort for vision. But as for indicators below the established value, the permissible difference is no more than 10%. This is the absolute minimum, below which you cannot fall.

Emergency lighting should ensure normal visibility during evacuation.