Light is necessary for a person to live normally. It affects almost all aspects of his life, mental state and physiology. If lighting standards are met, the room is pleasant to be in, fatigue occurs more slowly during work. Otherwise, the mood quickly deteriorates, and other signs of the negative impact of the “wrong” light on the eyes and nervous system appear.

What is illumination

Many people confuse illumination with the brightness of lamps, but this is wrong. The same lighting fixture can create different light levels, depending on the area of ​​the room, the height of the lamp, its angle of inclination.

Brightness, or luminous flux, is measured in lumens. This indicator is on the packaging of the lighting device, but, unfortunately, it is not always reliable. Therefore, to select an energy-saving lamp, it makes sense to take a compact RADEX LUPIN luxmeter with you to the store. The same device will help measure the illumination of your workplace and rooms at home. The parameter reflects the number of lumens luminous flux, which falls on 1 sq. m of surface. It is very important to prevent non-compliance with established standards.

What are the dangers of too little or too much lighting?

It is known that employees of some shopping centers often complain of watery eyes, fatigue and redness of the eyes. The reason is too bright lighting. On the one hand, it helps buyers take a better look at the product. On the other hand, it harms the health of the visual apparatus of workers who are under such lighting all day long.

When checking light level inspectors make orders only if the indicators do not reach the lower limits of the norm. This is because if the light is too dim, working conditions worsen. A person has difficulty doing work, his eyes get tired quickly, and myopia or farsightedness appears.

However, not only dim light, but also excessively bright light is harmful to the visual apparatus. Consequences of prolonged stay in a room with too much light:

• Irritation and redness of the mucous membrane (conjunctiva).
• Feeling of dryness and “powdery” eyes.
• The appearance of irritability.
• Feeling of general discomfort.
• Nervous overexcitation.

It follows from this: it is necessary to monitor not only compliance lighting standards, but also in the absence of a significant excess of the established values.

How measure illumination on one's own

Each of us can provide ourselves comfortable conditions work and rest. In particular, by creating adequate lighting. To do this, you need to install devices that produce light of normal brightness.

Check if it meets the standard light level your room or workplace, will help lux meter RADEX LUPIN. With this device you can always determine the brightness of light in any room. The measurement is simple. Place the light meter on the control surface with the photosensor pointing upward. The parameter value will be displayed on the device monitor in lux (lx).

The RADEX LUPIN lux meter provides correct information, unlike many other models. The error of its measurements does not exceed 10%. The accuracy of the device is ensured by corrective filters that block ultraviolet and infrared rays that are not perceived by the human eye. Since the spectrum of some light sources contains both, illuminance measurement without filters it turns out inaccurate. The RADEX LUPIN lux meter meets the requirements of GOST. Its spectral sensitivity is the same as that of the human eye, so it provides complete, reliable information about the light environment.

Briefly about lighting standards

Lighting in which a person maintains working capacity for a long time and does not notice an unreasonable deterioration in well-being or mood is considered normal. For control lighting standards The Chief State Doctor of the Russian Federation approved special sanitary rules and regulations. The document establishes clear requirements for lighting in premises for various purposes.

Standards for some of them (in suites):

• Bathrooms, bathrooms - 50.
• Sleeping quarters - 100.
• Living rooms and kitchens - 150.
• Gyms - 200.
• Playrooms for kindergartens - 200.
• Office rooms - 300.
• Classrooms - 300.
• Library premises - 400
• Doctors' offices and treatment rooms - 500.
• Trading rooms - 500.

The highest requirements are set for premises in which work of the highest precision is carried out. For example, for jewelry, engraving and watchmaking workshops, the illumination level should be 3000 lux. The lighting of storerooms, basements, attics, passage corridors and other rooms with short stays of people (20-30 lux) can be relatively dim.

Why measure illumination? It has been proven that bad (or, on the contrary, too good) light through the retina of the eye affects the working processes of the brain. And as a result, the state of a person. Insufficient lighting depresses, performance decreases, and drowsiness appears. Too bright light, on the contrary, excites and helps to connect additional resources of the body, causing their increased wear and tear.

Measurement of illumination of workplaces is carried out together with measurements of noise levels, dust and pollution, vibration - in accordance with SanPin (sanitary rules and regulations). Doctors are sure that regular insufficient lighting causes fatigue, decreased visual acuity, and reduces concentration. That is, there are all the prerequisites for an accident.

Bad light also affects other living beings: plants, animals. It is a well-known fact that plants grow poorly without light. But insufficient lighting also affects animals. Consequences: impaired growth and development, decreased productivity, poor weight gain, impaired reproductive function.

What is illumination?

Illumination is the ratio of the luminous flux to the area on which it falls. Moreover, it must fall on this plane exactly perpendicularly. Measured in lux, lux. One lux is equal to the ratio of one lumen to one square meter of surface. Lumen is a unit of measurement of luminous flux. This is in the system of international units. In England and America, the units used to measure illumination are lumens per square foot. Or footcandle. This is the illuminance from a light source of one candela at a distance of one foot from the surface.

In Europe there is a standard for lighting workspaces. Here are some recommendations from it: lighting in an office where you don’t need to look small parts should be about 300 lux. If the work process during the day takes place at the computer or involves reading, lighting of about 500 lux is recommended. The same lighting is expected in meeting rooms. At least 750 lux in areas where technical drawings are prepared or read.

Lighting can be natural or artificial. Sources natural light are, of course, the sun, the moon (more precisely, the light of the sun reflected by it), the scattered light of the sky (this poetic name is used even in protocols for measuring illumination). Sources artificial lighting are, of various kinds, shapes and designs, lamps and luminaires, light from computer and mobile device displays, TV screens, etc.

Based on the name of the unit of illumination (lux), the name of the device with which it is measured is a lux meter. This is a mobile, portable device for measuring illumination, the operating principle of which is identical to a photometer.

A stream of light hitting a photocell releases a stream of electrons in the body of the semiconductor. Thanks to this, the photocell begins to conduct electric current. The magnitude of this current is directly proportional to the illumination of the photocell. It is reflected on the scale. In analog lux meters, the scale is graduated in lux, the result is determined by the deflection of the needle.

Now analogue ones are being replaced by digital devices for measuring illumination. In them, the measurement result is displayed on a liquid crystal display. The measuring part in many of them is located in a separate housing and is connected to the device by a flexible wire. This allows measurements to be taken in hard-to-reach places. Thanks to a set of light filters, the limits of its measurements can be adjusted. In this case, the instrument readings must be multiplied by certain coefficients. The error of the lux meter, according to GOST, should be no more than 10%.

How is illumination measured?

The use of any methods for measuring illumination is impossible without a lux meter. Moreover, the rule is observed: the device is always in a horizontal position. It is installed at the required points. The State Standards contain diagrams of the location of these points and methods for their calculations.

Until recently, in Russia, GOST 24940-96 was used to measure illumination. This is an interstate standard for measuring illumination. This GOST uses concepts such as: illuminance, average, minimum and maximum illuminance, cylindrical illuminance, natural illuminance factor (KEO), safety factor, relative spectral luminous efficiency of monochromatic radiation.

In 2012, Russia introduced its own national standard for measuring illumination, GOST R 54944-2012. In this GOST, the following concepts have been added to those that existed before: emergency lighting, security lighting, working lighting, backup lighting, semi-cylindrical lighting, evacuation lighting. Both GOSTs describe in detail methods for measuring illumination.

Measurements are carried out separately for artificial and natural lighting. In this case, you need to make sure that no shadow falls on the device, and that there is no source of electromagnetic radiation nearby. This will interfere with the results. After all the necessary measurements of illumination have been made, based on the results obtained, using special formulas, the necessary parameters are calculated, and a general assessment is made. That is, the obtained parameters are compared with the standard, and a conclusion is made about whether the illumination of a given room or area is sufficient.

A separate protocol is filled out for each type of measurement in each room or section of the street. An assessment protocol is issued both for each room or territory, and for the entire facility. This is required by GOST. “Illumination measurement” must be carried out according to the rules.

What kind of light do you need?

Research in this area shows that cold light reduces the level of drowsiness and improves concentration. This is explained by suppression by short waves (ultraviolet, Blue colour) melatonin. This is a hormone that regulates circadian rhythms. And if this light is also bright, it will help cope with depression. The main thing is not to overdo it. Otherwise, from one extreme you can end up in the other, causing sleep disturbances. Lighting with cool light should be moderate during the day. And this is with sufficient illumination, which will not force you to strain your eyesight or, conversely, squint.

In the evening, on the contrary, muted light in warm colors is preferable. It promotes relaxation good rest, going to bed. Sharp and bright flashes of light, especially cold tones, should be avoided.

Of course, one-time violations of these rules will not cause serious health problems. But if this happens regularly, problems with impaired body functions cannot be avoided. Such a thing as light only at first glance seems like a trifle. Periodic monitoring of it and measurement of illumination are necessary.

Any light source is a source of luminous flux, and the greater the luminous flux that hits the surface of the illuminated object, the better this object is visible. And the physical quantity, numerically equal to the luminous flux incident per unit area of ​​the illuminated surface, is called illumination.

Illumination is denoted by the symbol E, and its value is found using the formula E = Ф/S, where Ф is the luminous flux, and S is the area of ​​the illuminated surface. In the SI system, illumination is measured in Lux (Lx), and one Lux is the illumination at which the luminous flux falling on one square meter of the illuminated body is equal to one Lumen. That is, 1 Lux = 1 Lumen / 1 Sq.m.

As an example, here are some typical illumination values:

Sunny day in mid-latitudes - 100,000 lux;

Cloudy day in mid-latitudes - 1000 Lux;

A bright room illuminated by the rays of the sun - 100 Lux;

Artificial lighting on the street - up to 4 lux;

Light at night with a full moon - 0.2 Lux;

The light of the starry sky on a dark moonless night is 0.0003 Lux.

Imagine that you are sitting in dark room with a flashlight and trying to read a book. To read, you need an illumination of at least 30 Lux. What will you do? First, you bring the flashlight closer to the book, which means the illumination is related to the distance from the light source to the illuminated object. Secondly, you place the flashlight at a right angle to the text, which means the illumination also depends on the angle at which this surface is illuminated. Thirdly, you can simply get a more powerful flashlight, since it is obvious that the illumination is greater, the higher the light intensity of the source.

Let's say a light flux hits some screen located at some distance from the light source. Let us double this distance, then the illuminated part of the surface will increase in area by 4 times. Since E = Ф/S, the illumination will decrease by as much as 4 times. That is, illumination is inversely proportional to the square of the distance from a point source of light to the illuminated object.

When a beam of light falls at right angles to a surface, the luminous flux is distributed over smallest area, if the angle is increased, the area will increase, and accordingly, the illumination will decrease.

As noted above, illumination is directly related to the intensity of light, and the greater the intensity of light, the greater the illumination. It has long been established experimentally that illumination is directly proportional to the intensity of the light source.

Of course, the illumination decreases if the light is obstructed by fog, smoke or dust particles, but if the illuminated surface is located at right angles to the light source, and the light propagates through clean, transparent air, then the illumination is determined directly by the formula E = I / R2, where I is the luminous intensity, and R is the distance from the light source to the illuminated object.

In America and England, the unit of illumination used is Lumen per square foot or Foot-Candela, as a unit of illumination from a source with a luminous intensity of one candela, and located at a distance of one foot from the illuminated surface.

Researchers have proven that through the retina of the human eye, light affects processes occurring in the brain. For this reason, insufficient illumination causes drowsiness and inhibits ability to work, and excessive illumination, on the contrary, excites, helps to activate additional resources of the body, however, wearing them out if this happens unjustifiably.

During the daily operation of lighting installations, a decrease in illumination is possible, therefore, to compensate this deficiency, even at the design stage of lighting installations, a special safety factor is introduced. It takes into account the decrease in illumination during operation lighting fixtures due to contamination, loss of reflective and transmitting properties of reflective, optical, and other elements of artificial lighting devices. Surface contamination, lamp failure, all these factors are taken into account.

For natural lighting, a reduction coefficient of KEO (natural illumination coefficient) is introduced, because over time, the translucent fillers of light openings may become dirty, and the reflective surfaces of the premises may become dirty.

The European standard defines lighting standards for different conditions, for example, if in the office you do not need to examine small details, then 300 Lux is enough, if people work at a computer - 500 Lux is recommended, if drawings are made and read - 750 Lux.

Illumination is measured with a portable device - a lux meter. Its operating principle is similar to a photometer. Light hits the surface, stimulating a current in the semiconductor, and the amount of current produced is precisely proportional to the illumination. There are analog and digital light meters.

Often the measuring part is connected to the device with a flexible spiral wire so that measurements can be taken in the most inaccessible, yet important places. A set of light filters is attached to the device to adjust the measurement limits taking into account the coefficients. According to GOST, the instrument error should be no more than 10%.

When measuring, follow the rule that the device must be positioned horizontally. It is installed one by one at each required point, according to the scheme of GOST R 54944-2012. GOST, among other things, takes into account security lighting, emergency lighting, evacuation lighting and semi-cylindrical lighting, and also describes the measurement method.

Measurements for artificial and natural are carried out separately, and it is important that no random shadow falls on the device. Based on the results obtained, using special formulas, a general assessment is made, and a decision is made whether something needs to be adjusted, or whether the illumination of the room or area is sufficient.

Andrey Povny

Poor lighting in premises, a workplace or a room in an apartment negatively affects human health, reduces concentration, performance, irritability and mental disturbances. Very bright light is also an irritant and does not provide anything positive for a person.

Therefore, it is necessary to ensure normal illumination of the premises, which is regulated by a certain SNiP standard. This requires easy installation appropriate lighting lamps for each room.

Illumination of premises in nominal terms is the flux of light that is emitted onto the surface at right angles per unit area. When light falls at an acute angle, the illumination decreases depending on the angle of inclination.

Illumination is measured in lux, which is equal to 1 lumen (unit of luminous flux) per m2.

The illumination of the premises directly depends on the strength of the light that comes from the source. The greater the distance from the light source to the surface, the lower the illumination parameter.

Norms

Each type of room has its own lighting standards. For example, for a grocery store, the highest pulsation value is set to 15%, illumination is 300 lux, but for the sporting goods department or building materials the norms are completely different. The rules also establish certain permissible illumination for clinics, kindergartens, car services and other facilities.

Example of illumination calculation

Let's determine the required lighting for the bedroom. The bedroom area is 25 m2. The value of the norm according to the rules for rooms of this type is multiplied by the area: 150 x 22 = 3300 lux. The total luminous flux of lighting devices at this level of illumination must be at least 3300 lumens.

Now all that remains is to choose the right lighting lamps for the bedroom. When choosing, you can, for example, purchase three such 12-watt lamps. This will ensure the creation of a luminous flux of 3600 lumens, as can be seen from the table values.

This calculation is approximate, since LED bulbs have various parameters light depending on the manufacturer. Thus, you can easily independently calculate the required power and type of lamps to create standardized illumination of any room in accordance with the rules of SNiP.

Instruments for measuring illumination

To measure room illumination, various devices are used, which have their own design features and measurement methods. Let's look at the main devices in more detail.

Luxmeter

Lux meters are divided into electronic and analog, which are no longer produced, and only old samples of such models remain.

This lux meter is used:

• Checking compliance of room illumination with regulatory data.
• Measuring lighting parameters when carrying out work to assess working conditions.
• During electrical installation work to compare illumination indicators with calculations for lighting devices.

The principle of operation of the lux meter is based on the operation of the built-in one, to which the flow of light is directed. In this case, a significant flow of charged particles appears in the photocell. As a result, a current appears electric current, the strength of which depends on the strength of the luminous flux directed at the photocell. Usually this parameter is displayed on the instrument scale.

Types of lux meters

Depending on the location of the sensor that measures room illumination, lux meters are divided into types:

Monoblock (one-piece device) . The sensor is fixed in the device body itself.

Device with remote sensor , connected by a flexible wire.

To produce simple measurements a regular monoblock lux meter is suitable, without auxiliary various functions. To determine several illumination parameters when performing professional calculations, it is necessary to use devices that have an additional set of functions. Such devices have built-in memory and can determine average parameter values.

A significant advantage for a lux meter is the presence of special light filters, which help to more accurately determine the value of the light intensity that comes from lighting devices with different shades colors.

The presence of a remote sensor in the lux meter makes it possible to determine the illumination with greater accuracy, since in this case the influence external factors decreases. Modern models have a liquid crystal display. It makes it much easier to take readings from the device.

Devices for photographic equipment

Photographic equipment uses devices such as exposure meters and exposure meters . They are designed to determine the parameters of brightness and exposure illumination. By determining the values ​​of these indicators, a professional photographer can obtain high-quality photographs.

Exposure meters are divided into types:

• Internal.
• External.

Flash meters

Such devices are designed to measure illumination when photographing. Wherein additional element use pulsed-type lighting devices (photo flashes). In modern camera models, the flash meter is located in the body. It changes the flash output at different light levels.

Professionals use flash meters with a remote sensor; they more accurately determine the illumination.

Photometer

Such a device is called a multimeter. He is more modern model flash meter. Its advantage is the combination of exposure meter and flash meter options.

Light pulsation

The uniformity of the luminous flux of lighting devices leaves much to be desired. The effect, expressed in the presence of fluctuations in the light flux, is not visible to the eye, but its impact on human health is of great importance.

The danger of such light is that it is visually impossible to determine the presence of light pulses. And as a result of their action, sleep may be disrupted, discomfort, depression, weakness, heart failure and other symptoms may occur.

The ripple parameter is its coefficient, which expresses the force of change in the flux of light directed per unit surface area over a period of time. The formula for calculating this coefficient is quite simple. The irradiance ripple factor is determined by the difference between the highest and lowest illuminance for a certain time, divided by twice the average illuminance, and the result is multiplied by 100%.

Sanitary regulations determine the upper limit of the pulsation coefficient. In the workplace it should be no more than 20%, and depends on the degree of responsibility of the employee’s work. The more responsible the work, the lower the lighting pulsation coefficient should be.

For administration premises and offices with intense visual work, this coefficient should not rise above the 5% mark. In this case, the flow of light with a pulsation frequency of up to 300 hertz is taken into account, since there is no point in taking a higher frequency into account, due to the fact that it is not perceived by the human eye and does not have a negative effect.

Determination of lighting pulsation

To determine the pulsation of light, an effective simple device is used that measures the brightness, pulsation and illumination of rooms, and is called a luxmeter-pulsometer-brightness meter.

Device functions

• Measuring the pulsation of light waves that occur when various lighting devices flicker.
• Measuring the lighting pulsation of computer monitors and other screens.
• Determination of room illumination.
• Determining the brightness of lighting devices and monitors.

The principle of operation of the device is to check the lighting level using a photosensor with further signal conversion and displaying the result on a liquid crystal display.

The light pulsation coefficient can be determined using a program on a computer, or you can analyze the measurements yourself. To analyze measurements on a computer, a special program “Ecolight-AP” is used, which works with the device “Ecolight-02”.

Distinctive features measuring instruments The factors that determine ripple are sensitivity levels, type of power supply and quality of photosensors.

The highest pulsation coefficient is produced by LED lamps, when using which this parameter sometimes reaches 100%. and have a low pulsation coefficient. Incandescent lamps have a pulsation coefficient of no higher than 25%. In this case, the cost and quality of the lamps do not play a role. Even expensive lamps can produce significant levels of light pulsation.

Methods for reducing lighting pulsation

• The use of lighting devices operating on alternating current with a frequency of more than 400 hertz.
• Installation of lighting fixtures for different phases with a three-phase network.
• Installation of a ballast compensation device () into the lighting device and special connection of offset lamps. The first lamp operates on a lagging current, and the 2nd on a leading current.
• Installation of lamps with electronic ballasts. They are equipped with an electronic ballast that smooths out ripples and stabilizes the voltage.

If lighting devices in a room are connected to one phase, then connecting them to different phases will be problematic. Therefore, it will be more convenient to purchase luminaires with electronic ballasts. Their advantage is that they comply with all regulations.

Controlling the level of lighting pulsation is necessary for human health, since deviations from the norms lead to disruption of the performance and well-being of employees.

For residential buildings, indoor lighting is also important. The pulsation of light is not visible, but over time its negative impact becomes apparent.

Currently, with a huge variety of lighting devices, the population does not have a common understanding of how illumination is measured. Often there is a misunderstanding with such technical characteristics, such as luminous intensity and brightness, lumens and candelas. When purchasing lighting fixtures, people often pay attention to the total luminous flux, without taking into account the loss of light and heat.

In this article:

Illumination concept

The luminous flux is measured under special laboratory conditions and cannot be determined spontaneously. Therefore, SNiP takes into account the amount of illumination, which, unlike the luminous flux, everyone can measure independently. It is a measure of the ratio of luminous flux, measured in lumens, to the surface area on which photons fall. The angle of incidence should be 90°. The unit of illumination is lux.

The dependence of a person’s psychological and physical states on light has long been established. If in low light the brain processes are depressed, then in bright light they are stimulated. But in any case, the retina and the body’s resources wear out. When designing lighting devices, a safety factor (SF) is determined, which should take into account the likely decline in illumination of the installation. For artificial light, the indicator provides for a decrease in brightness due to wear and tear of the optical components of the device and their natural contamination. The coefficient of natural illumination decreases due to changes in the reflective properties of surrounding objects.

Illumination measurements are carried out at workplaces along with determination of the level of pollution, sound vibrations, electromagnetic radiation, and in some industries, gamma radiation. The importance of knowing these parameters cannot be overestimated when creating optimal conditions labor, and all of them comply with sanitary rules and regulations. For example, the illumination should be:

• in the office - 300 lux;
• in the office for constant work with a computer - 500 lux;
• for technical and design bureaus - 750 lux.

If there is natural lighting in the room, the level of artificial background can be reduced.

Instruments for determining the level of illumination and methods for determining it

The name of the device is similar to the name of the value it sets - lux meter. The operating principle of a small-sized portable device resembles the operation of a photometer. The radiation flow, falling on the photosensitive element of the semiconductor, tears off electrons, which begin to move in an orderly manner. Thus, the electrical circuit is closed. Moreover, the current value is directly proportional to the intensity of illumination of the photocell, which is reflected on the scale of an analog lux meter. Today, instruments with arrows have practically disappeared, they have been replaced by digital ones. They are equipped with liquid crystal displays, in which the photosensitive sensor itself is located in a separate housing, and it is connected to the display using a flexible wire.

During the experiment to measure illumination, the device is installed in a horizontal position. Moreover, in accordance with the requirements of GOST, they are placed in different points of the room, according to a certain scheme. In 2012, Russia adopted a new standard for measuring the characteristics of the amount of luminous flux. In the old conceptual apparatus, when measuring, terms of a given quantity were used such as:

• minimum, average, maximum, cylindrical;
• natural;
• stock gradient;
• relative efficiency of coherent beam flow.

Currently, the following types of lighting have been added to them:

• emergency;
• working;
• security;
• evacuation;
• backup

The standard describes in detail all the intricacies of conducting measurement studies.

Measurements are carried out separately for natural and artificial illumination. During the experiment, it is impossible to allow even the slightest shadow to fall on the device, and there should be at least 1 source of electromagnetic waves nearby. All of them interfere with the operation of the device.

After performing the necessary illumination measurements, the required value is determined. It is compared with the standard value. Then the results are summed up about the sufficiency of illumination of the territory or room. Each type of measurement test is documented in a special evaluation protocol, which is required by GOST.

Measuring the amount of light for LED devices and examples in nature

LED lamps have become very popular due to their unique energy efficiency. But LEDs and their power supplies emit heat when illuminated, which is dissipated using heat-conducting materials (aluminum) and design features(ribs, large radiator area). Despite the apparent lack of connection between heat loss and illumination, experts always take it into account when creating new devices.

Difficulties with the operation of LED lamps begin when operating in conditions where the temperature rises above +50°C. Why is it recommended to measure the illumination of LEDs after 2 hours of their operation, i.e. after reaching optimal mode. To eliminate the occurrence of errors, repeated measurements are taken during the work shift. It is advisable to carry out these studies at least once a year. In order to eliminate any errors during design, a light reduction coefficient is set, depending on the physical characteristics of the object.

Typically, manufacturers of LED devices provide a guarantee of their flawless operation for 3 years. All operating parameters of such lamps, including illumination, must correspond to the declared values. If the operating conditions of the devices occur at outdoor temperatures above 45°C, then light measurements must be taken much more often. Otherwise, incorrect design and the results obtained will lead to a rapid drop in lighting performance.

As for examples of illumination in nature, in the Earth’s orbit and the equator at noon this value is equal to 135 thousand lux. On a sunny day it is up to 100 thousand lux, on a cloudy day it is only 1 thousand lux, but from the Moon it is only 0.2 lux. Measuring light on the street at the latitude of Moscow in winter period showed from 4 to 5 thousand lux. On a moonless night, the illumination is a thousand times less than on a full moon, and with 10-point cloudiness it is 10 thousand times less. What is used to measure the illumination in a room and natural conditions, refers to physical quantities included in the International System of Units.