Sveta. This article will reveal to readers the properties of photons, which will allow them to determine why light comes in different brightnesses.

Particle or wave?

At the beginning of the twentieth century, scientists were puzzled by the behavior of light quanta - photons. On the one hand, interference and diffraction spoke of their wave essence. Therefore, light was characterized by properties such as frequency, wavelength, and amplitude. On the other hand, they convinced the scientific community that photons transfer momentum to surfaces. This would be impossible if the particles did not have mass. Thus, physicists had to admit: electromagnetic radiation is both a wave and a material object.

Photon energy

As Einstein proved, mass is energy. This fact proves our central luminary, the Sun. A thermonuclear reaction turns a mass of highly compressed gas into pure energy. But how to determine the power of the emitted radiation? Why in the morning, for example, is the luminous intensity of the sun lower than at noon? The characteristics described in the previous paragraph are interconnected by specific relationships. And they all point to the energy that electromagnetic radiation carries. This value changes upwards when:

• decrease in wavelength;
• increasing frequency.

What is the energy of electromagnetic radiation?

A photon is different from other particles. Its mass, and therefore its energy, exists only as long as it moves through space. When colliding with an obstacle, a quantum of light increases its internal energy or gives it a kinetic moment. But the photon itself ceases to exist. Depending on what exactly acts as an obstacle, various changes occur.

1. If the obstacle is a solid body, then most often the light heats it up. The following scenarios are also possible: a photon changes direction, stimulates a chemical reaction, or causes one of the electrons to leave its orbit and go to another state (photoelectric effect).
2. If the obstacle is a single molecule, for example, from a rarefied gas cloud in outer space, then a photon makes all its bonds vibrate more strongly.
3. If the obstacle is a massive body (for example, a star or even a galaxy), then the light is distorted and changes the direction of motion. This effect is based on the ability to "look" into the distant past of the cosmos.

Science and Humanity

Scientific data often seem to be something abstract, inapplicable to life. This also happens with the characteristics of light. When it comes to experimenting or measuring the radiation of stars, scientists need to know the absolute values ​​(they are called photometric). These concepts are usually expressed in terms of energy and power. Recall that power refers to the rate of change of energy per unit of time, and in general it shows the amount of work that the system can produce. But man is limited in his ability to sense reality. For example, the skin feels heat, but the eye does not see the photon of infrared radiation. The same problem with units of luminous intensity: the power that radiation actually shows is different from the power that the human eye can perceive.

Spectral sensitivity of the human eye

We remind you that the discussion below will focus on average indicators. All people are different. Some do not perceive individual colors at all (colorblind). For others, the culture of color does not coincide with the accepted scientific point of view. For example, the Japanese do not distinguish between green and blue, and the British - blue and blue. In these languages, different colors are denoted by one word.

The unit of luminous intensity depends on the spectral sensitivity of the average human eye. The maximum daylight falls on a photon with a wavelength of 555 nanometers. This means that in the light of the sun, a person sees the green color best. Night vision maximum is a photon with a wavelength of 507 nanometers. Therefore, under the moon, people see blue objects better. At dusk, everything depends on the lighting: the better it is, the more “green” the maximum color that a person perceives becomes.

The structure of the human eye

Almost always, when it comes to vision, we say what the eye sees. This is an incorrect statement, because the brain perceives first of all. The eye is only an instrument that transmits information about the light output to the main computer. And, like any tool, the entire color perception system has its limitations.

There are two different types of cells in the human retina - cones and rods. The former are responsible for daytime vision and perceive colors better. The latter provide night vision, thanks to the sticks, a person distinguishes between light and shadow. But they do not perceive colors well. The sticks are also more sensitive to movement. That is why, if a person walks through a moonlit park or forest, he notices every swaying of the branches, every breath of the wind.

The evolutionary reason for this separation is simple: we have one sun. The moon shines by reflected light, which means that its spectrum does not differ much from the spectrum of the central luminary. Therefore, the day is divided into two parts - illuminated and dark. If people lived in a system of two or three stars, then our vision would probably have more components, each of which was adapted to the spectrum of one luminary.

I must say, on our planet there are creatures whose eyesight is different from human. Desert dwellers, for example, detect infrared light with their eyes. Some fish can see near ultraviolet, as this radiation penetrates the deepest into the water column. Our pet cats and dogs perceive colors differently, and their spectrum is reduced: they are better adapted to chiaroscuro.

But people are all different, as we mentioned above. Some representatives of mankind see near infrared light. This is not to say that they would not need thermal cameras, but they are able to perceive slightly redder shades than most. Others have developed the ultraviolet part of the spectrum. Such a case is described, for example, in the film "Planet Ka-Pax". The protagonist claims that he came from another star system. The examination revealed that he had the ability to see ultraviolet radiation.

Does this prove that Prot is an alien? No. Some people can do it. In addition, the near ultraviolet is closely adjacent to the visible spectrum. No wonder some people take a little more. But Superman is definitely not from Earth: the X-ray spectrum is too far from the visible for such vision to be explained from a human point of view.

Absolute and relative units for determining the luminous flux

A quantity independent of the spectral sensitivity, which indicates the flow of light in a known direction, is called a "candela". The power unit, already with a more "human" attitude, is pronounced the same way. The difference is only in the mathematical designation of these concepts: the absolute value has a subscript "e", relative to the human eye - "υ". But do not forget that the sizes of these categories will vary greatly. This must be taken into account when solving real problems.

Enumeration and comparison of absolute and relative values

To understand what the power of light is measured in, it is necessary to compare the "absolute" and "human" values. On the right are purely physical concepts. On the left are the values ​​into which they turn when passing through the system of the human eye.

1. The power of radiation becomes the power of light. Concepts are measured in candela.
2. Energy brightness turns into brightness. The values ​​are expressed in candela per square metre.

Surely the reader saw familiar words here. Many times in their lives, people say: "Very bright sun, let's go into the shade" or "Make the monitor brighter, the movie is too gloomy and dark." We hope the article will slightly clarify where this concept came from, as well as what the unit of luminous intensity is called.

Features of the concept of "candela"

We have already mentioned this term above. We also explained why the same word is used to refer to completely different concepts of physics related to the power of electromagnetic radiation. So, the unit of measure for the intensity of light is called the candela. But what is it equal to? One candela is the intensity of light in a known direction from a source that emits strictly monochromatic radiation with a frequency of 5.4 * 10 14, and the energy force of the source in this direction is 1/683 watts per unit solid angle. The reader can easily convert frequency into wavelength, the formula is very easy. We will prompt: the result lies in visible area.

The unit of measurement for the intensity of light is called the "candela" for a reason. Those who know English remember that a candle is a candle. Previously, many areas of human activity were measured in natural parameters, for example, horsepower, millimeters of mercury. So it is not surprising that the unit of measurement for the intensity of light is the candela, one candle. Only a candle is very peculiar: with a strictly specified wavelength, and producing a specific number of photons per second.

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Initial value

Converted value

Candela Candle (German) Candle (UK) Decimal Candle Pentane Candle Pentane Candle (10 St) Hefner Candle Unit Carcel Candle Decimal (French) Lumen/Steradian Candle (International)

More about the power of light

General information

The intensity of light is the power of the luminous flux within a certain solid angle. That is, the strength of light does not determine all the light in space, but only the light emitted in a certain direction. Depending on the light source, the light intensity decreases or increases as the solid angle changes, although sometimes this value is the same for any angle, as long as the source spreads the light evenly. The strength of light is a physical property of light. In this it differs from brightness, since in many cases when people talk about brightness, they mean a subjective sensation, and not a physical quantity. Also, the brightness does not depend on the solid angle, but is perceived in the general space. The same source with a constant light intensity can be perceived by people as light of different brightness, since this perception depends on the surrounding conditions and on the individual perception of each person. Also, the brightness of two sources with the same luminous intensity can be perceived differently, especially if one gives diffused light, and the other - directional. In this case, the directional source will appear brighter, despite the fact that the light intensity of both sources is the same.

Light intensity is considered as a unit of power, although it differs from the usual concept of power in that it depends not only on the energy emitted by the light source, but also on the wavelength of the light. Human sensitivity to light depends on the wavelength and is expressed as a function of the relative spectral luminous efficiency. The intensity of light depends on the luminous efficiency, which reaches a maximum for light with a wavelength of 550 nanometers. This is green. The eye is less sensitive to light with longer or shorter wavelengths.

In the SI system, luminous intensity is measured in candelach(cd). One candela is approximately equal to the intensity of light emitted by one candle. Sometimes an obsolete unit is also used, candle(or international candle), although in most cases this unit has been replaced by candela. One candle is approximately equal to one candela.

If you measure the intensity of light using a plane that shows the propagation of light, as in the illustration, you can see that the amount of light intensity depends on the direction to the light source. For example, if we take the direction of maximum radiation of an LED lamp as 0°, then the measured luminous intensity in the direction of 180° will be much lower than for 0°. For diffuse sources, the magnitude of the luminous intensity for 0° and 180° will not differ much, and may be the same.

In the illustration, the light emitted by two sources, red and yellow, covers an equal area. Yellow light is diffuse, like candlelight. Its strength is approximately 100 cd, regardless of direction. Red - on the contrary, directed. In the direction of 0°, where the radiation is maximum, its strength is 225 cd, but this value decreases rapidly when deviating from 0°. For example, the luminous intensity is 125 cd when directed at a source of 30° and only 50 cd when directed at 80°.

The power of light in museums

Museum staff measure the intensity of light in museum spaces to determine the optimal conditions for visitors to view the exhibited works, while at the same time providing gentle light that does as little harm to the museum exhibits as possible. Museum exhibits containing cellulose and dyes, especially those made from natural materials, deteriorate from prolonged exposure to light. Cellulose provides strength to fabric, paper, and wood products; often in museums there are many exhibits of these materials, so the light in the exhibition halls is a great danger. The stronger the light intensity, the more the museum exhibits deteriorate. In addition to being destroyed, light also discolours or yellows cellulose materials such as paper and fabrics. Sometimes the paper or canvas on which the paintings are painted deteriorates and breaks down faster than the paint. This is especially problematic, since the colors in the picture are easier to restore than the base.

The harm done to museum exhibits depends on the wavelength of the light. So, for example, light in the orange spectrum is the least harmful, and blue light is the most dangerous. That is, longer wavelength light is safer than shorter wavelength light. Many museums use this information and not only control the total amount of light, but also limit the blue light using light orange filters. At the same time, they try to choose filters so light that, although they filter blue light, they allow visitors to fully enjoy the works exhibited in the exhibition hall.

It is important not to forget that exhibits deteriorate not only from light. Therefore, it is difficult to predict, based only on the strength of light, how quickly the materials from which they are made break down. For long-term storage in museum premises, it is necessary not only to use low lighting, but also to maintain low humidity, as well as a low amount of oxygen in the air, at least inside the display cases.

In museums where it is forbidden to take pictures with a flash, they often refer to the harm of light for museum exhibits, especially ultraviolet. This is practically unfounded. Just as limiting the entire spectrum of visible light is much less effective than limiting blue light, banning flashes has little effect on the extent of light damage to exhibits. During the experiments, the researchers noticed slight damage to watercolors caused by professional studio flash only after over a million flashes. A flash every four seconds at a distance of 120 centimeters from the exhibit is almost equivalent to the light that usually happens in the exhibition halls, where the amount of light is controlled and blue light is filtered. Those who take photos in museums rarely use such powerful flashes, as most visitors are not professional photographers and take pictures with phones and compact cameras. Every four seconds, flashes in the halls rarely work. The damage from the ultraviolet rays emitted by the flash is also small in most cases.

Luminous intensity of lamps

It is customary to describe the properties of fixtures with the help of luminous intensity, which differs from the luminous flux - a quantity that determines the total amount of light, and shows how bright this source is in general. It is convenient to use the intensity of light to determine the lighting properties of lamps, for example, LEDs. When buying them, information about the intensity of light helps to determine with what strength and in which direction the light will spread, and whether such a lamp is suitable for the buyer.

Light intensity distribution

In addition to the light intensity itself, light intensity distribution curves help to understand how the lamp will behave. Such diagrams of the angular distribution of luminous intensity are closed curves in a plane or in space, depending on the symmetry of the lamp. They cover the entire area of ​​light distribution of this lamp. The diagram shows the magnitude of the luminous intensity depending on the direction of its measurement. The graph is usually built either in polar or rectangular coordinate systems, depending on which light source the graph is being built for. It is often placed on lamp packaging to help the customer imagine how the lamp will behave. This information is important for designers and lighting technicians, especially those who work in the field of cinema, theater, and the organization of exhibitions and performances. Light intensity distribution also affects driving safety, so engineers designing vehicle lighting use light intensity distribution curves. They must comply with strict rules governing the distribution of light intensity in headlights in order to ensure maximum safety on the roads.

The example in the figure is in the polar coordinate system. A is the center of the light source from where the light spreads in different directions, B is the luminous intensity in candela, and C is the angle of measurement of the direction of the light, with 0° being the direction of the maximum luminous intensity of the source.

Measuring the strength and distribution of light intensity

The strength of light and its distribution are measured with special instruments, goniophotometers and goniometers. There are several types of these devices, for example, with a movable mirror, which allows you to measure the intensity of light from different angles. Sometimes the light source itself moves instead of the mirror. Typically, these devices are large, with a distance of up to 25 meters between the lamp and the sensor that measures the intensity of the light. Some devices consist of a sphere with a measuring device, a mirror, and a lamp inside. Not all goniophotometers are large, there are also small ones that move around the light source during the measurement. When buying a goniophotometer, the price, size, power, and the maximum size of the light source that it can measure, among other factors, play a decisive role.

Half brightness angle

The half-brightness angle, sometimes also called the glow angle, is one of the quantities that helps describe a light source. This angle indicates how directed or diffused the light source is. It is defined as the angle of the light cone at which the luminous intensity of the source is equal to half of its maximum intensity. In the example in the figure, the maximum luminous intensity of the source is 200 cd. Let's try to determine the half-brightness angle using this graph. Half the luminous intensity of the source is equal to 100 cd. The angle at which the light intensity of the beam reaches 100 cd., that is, the angle of half brightness, is equal to 60+60=120° on the graph (half of the angle is shown in yellow). For two light sources with the same total amount of light, a narrower half-brightness angle means that its luminous intensity is greater, compared to the second light source, for angles between 0° and the half-brightness angle. That is, directional sources have a narrower half-brightness angle.

There are benefits to both wide and narrow half-brightness angles, and which one is preferred depends on the application of that light source. So, for example, for scuba diving, you should choose a flashlight with a narrow half-brightness angle, if visibility is good in the water. If the visibility is poor, then it makes no sense to use such a flashlight, since it only wastes energy in vain. In this case, a flashlight with a wide half-brightness angle that diffuses the light well is better. Also, such a flashlight will help during photo and video shooting, because it illuminates a wider area in front of the camera. Some dive lights allow you to manually adjust the half brightness angle, which is handy as divers can't always predict what visibility will be where they dive.

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The question of what the luminous flux is measured in began to matter to users of lighting devices only when types of lamps appeared, the brightness of which did not equal the power consumption, measured in watts.

Let's figure out how the concept of brightness is connected with the concept of illumination, as well as how you can imagine the distribution of the flow of light throughout the room and choose the right lighting device.

What is luminous flux?

The flux of light is the power of light radiation visible to the human eye; light energy emitted by a surface (luminous or reflective). The energy of the light flux is measured in lumen-seconds and corresponds to a flux of 1 lumen, emitted or perceived in 1 second. This figure describes the total flow, not taking into account the concentrating efficiency of the entire device. This estimate also includes scattered, useless light, so the same number of lumens can be found in sources of different designs.

It is necessary to distinguish between the light value and the energy value - the latter characterizes light, regardless of its property to cause visual sensations. Each photometric light quantity has an analogue that can be quantified in units of energy or power. For light energy, such an analogue is the radiation energy (radiant energy), measured in joules.

Luminous flux unit

1 lumen is the light emitted by a source with a luminous intensity of 1 candela within a solid angle of 1 steradian. A 100-watt incandescent light bulb generates approximately 1,000 lumens of light. The brighter the light source, the more lumens it emits.

In addition to lumens, there are other units of measurement that allow you to characterize light. It is possible to measure the spatial and surface flux density - this is how we find out the strength of light and illumination. Light intensity is measured in candela, illuminance is measured in lux. But it is more important for the consumer to figure out in what units the brightness of light bulbs and other lighting fixtures is indicated in the sale. Some manufacturers report the number of lumens per watt. This is how the luminous efficiency (light output) is measured: how much light a lamp gives out, spending 1 watt.

Defining Formulas

Since any light source emits it unevenly, the number of lumens does not fully characterize the lighting fixture. You can calculate the intensity of light in candela by dividing its flux, expressed in lumens, by the solid angle, measured in steradians. Using this formula, it will be possible to take into account the totality of rays coming from the source when they cross the surface of an imaginary sphere, forming a circle on it.

But the question arises, what gives in practice the number of candela that we find; it is impossible to find a suitable LED or flashlight only by the luminous intensity parameter, you also need to take into account the ratio of the scattering angle, which depends on the design of the device. When choosing lamps that shine evenly in all directions, it is important to understand whether they are suitable for the buyer's goals.

If earlier light bulbs in different rooms were selected based on the number of watts, then before buying LED lamps, you will have to calculate their total brightness in lumens, and then divide this figure by the area of ​​the room. This is how illumination is calculated, which is measured in lux: 1 lux is 1 lumen per 1 m². There are lighting standards for rooms for various purposes.

Luminous flux measurement

Before releasing products to the market, the manufacturer makes in the laboratory the definition and measurement of the characteristics of the lighting device. At home, without special equipment, this is unrealistic to do. But you can check the numbers indicated by the manufacturer using the above formulas using a compact light meter.

The difficulty of accurately measuring the parameters of light lies in the fact that it comes in all possible directions of propagation. Therefore, laboratories use spheres with an inner surface that has a high reflectivity - spherical photometers; they are also used to measure the dynamic range of cameras, i.e. photosensitivity of their matrices.

In everyday life, it makes more sense to measure such important light parameters as room illumination and pulsation coefficient. High ripple and dim lighting cause people to strain their eyes too much, which causes fatigue more quickly.

The pulsation coefficient of the light flux is an indicator that characterizes the degree of its unevenness. Permissible levels of these coefficients are regulated by SanPiN.

It is not always possible to see with the naked eye that the light bulb is flickering. Nevertheless, even a slight excess of the pulsation coefficient affects the central nervous system of a person negatively, and also reduces performance. Light that can pulsate unevenly is emitted by all screens: computer and laptop monitors, tablet and mobile phone displays, and a TV screen. Pulsation is measured with a luxmeter-pulsemeter.

What is a candela?

Another important characteristic of the light source is the candela, which is included in the 7 units of the International System of Units (SI) adopted by the General Conference on Weights and Measures. Initially, 1 candela was equal to the radiation of 1 candle, taken as a standard. Hence the name of this unit of measurement. Now it is determined by a special formula.

Candela is the intensity of light, measured exclusively in a given direction. The spread of rays on the part of the sphere outlined by a solid angle allows us to calculate a value equal to the ratio of the luminous flux to this angle. Unlike lumens, this value is used to determine the intensity of the rays. This does not take into account useless, scattered light.

A flashlight and a ceiling lamp will have a different cone of light, as the rays fall at different angles. Candelas (more precisely, millicandelas) are used to indicate the luminous intensity of sources with a directional glow: indicator LEDs, flashlights.

Lumens and Lux

In lumens, the amount of light flux is measured, this is a characteristic of its source. The number of rays that reached any surface (reflecting or absorbing) will already depend on the distance between the source and this surface.

The level of illumination is measured in lux (lx) with a special device - a luxmeter. The simplest luxmeter consists of a selenium photocell that converts light into electric current energy, and a pointer microammeter that measures this current.

The spectral sensitivity of the selenium photocell differs from the sensitivity of the human eye, so in different conditions it is necessary to use correction factors. The simplest light meters are designed to measure one type of illumination, such as daylight. Without the use of coefficients, the error can be more than 10%.

High-class luxmeters are equipped with light filters, special spherical or cylindrical nozzles (for measuring spatial illumination), fixtures for measuring brightness and checking the sensitivity of the device. Their level of error is about 1%.

Poor illumination of the premises contributes to the development of myopia, has a bad effect on performance, causes fatigue, and a decrease in mood.

The minimum illumination of the computer table surface according to SanPiN is 400 lux. School desks must have at least 500 lux illumination.

Lumen and watt

Energy-saving lamps with the same light output consume 5-6 times less electrical energy than incandescent lamps. LED - 10-12 times less. The power of the light flux no longer depends on the number of watts. But manufacturers always indicate watts, since the use of too powerful light bulbs in cartridges not designed for such a load leads to damage to electrical appliances or a short circuit.

If you arrange the most common types of light bulbs in ascending order of light output, you can get the following list:

1. Incandescent lamp - 10 lumens / watt.
2. Halogen - 20 lumens / watt.
3. Mercury - 60 lumens / watt.
4. Energy saving - 65 lumens/watt.
5. Compact fluorescent lamp - 80 lumens/watt.
6. Metal halide - 90 lumens / watt.
7. Light-emitting diode (LED) - 120 lumens / watt.

But most people are accustomed to looking at the number of watts indicated by the manufacturer when buying light bulbs. To calculate how many watts per square meter you need, you first need to decide how bright the light in the room should be. 20 watt incandescent lamps per 1 m² - such lighting is suitable for a workplace or living room; for a bedroom, 10-12 watts per 1 m² will be enough. When buying energy-saving lamps, these figures are divided by 5. It is important to take into account the height of the ceiling: if it is higher than 3 m, the total number of watts should be multiplied by 1.5.

Anyone who begins to study the characteristics of lamps and certain types of lamps is sure to come across such concepts as illumination, luminous flux and luminous intensity. What do they mean and how do they differ from each other?

Let's try to understand these quantities in simple, understandable words. How they are interconnected, their units of measurement and how the whole thing can be measured without special instruments.

What is luminous flux

In the good old days, the main parameter by which a light bulb was chosen in the hallway, in the kitchen, in the hall, was its power. No one ever thought to ask in the store about some kind of lumens or candela.

Today, with the rapid development of LEDs and other types of lamps, going to the store for new items is accompanied by a bunch of questions not only about the price, but also about their characteristics. One of the most important parameters is the luminous flux.

In simple terms, luminous flux is the amount of light that a lamp gives.

However, do not confuse the luminous flux of individual LEDs with the luminous flux of assembled fixtures. They may differ significantly.

It must be understood that the luminous flux is just one of the many characteristics of a light source. Moreover, its value depends on:

• from source power

Here is a table of this dependence for LED lamps:

And these are tables of their comparison with other types of incandescent lamps, fluorescent, DRL, HPS:

Incandescent light bulbFluorescent Lamp Halogen HPS DRL

However, there are nuances here. LED technology is still developing and it is quite possible that LED bulbs of the same power, but from different manufacturers, will have completely different luminous fluxes.

It's just that some of them have gone more forward, and have learned to shoot more lumens per watt than others.

Someone will ask what all these tables are for? So that sellers and manufacturers do not stupidly deceive you.

On the box they will beautifully write:

• power 9W

• light output 1000lm

• analogue of incandescent lamp 100W

What will you look at first? That's right, for what is more familiar and understandable - the indicators of an analogue of an incandescent lamp.

But with such power, you will not be close to the old light. Start swearing at LEDs and the technology of their imperfections. And the point is that it turns out to be an unscrupulous manufacturer and his product.

• from efficiency

That is, how efficiently a particular source converts electrical energy into light. For example, an ordinary incandescent lamp has a return of 15 lm / W, and a high-pressure sodium lamp has a return of 150 lm / W.

It turns out that this is 10 times more efficient source than a simple light bulb. With the same power, you have 10 times more light!

The luminous flux is measured in Lumens - Lm.

What is 1 Lumen? During the day in normal light, our eyes are most sensitive to green. For example, if we take two lamps with the same power of blue and green, then green will seem brighter for all of us.

The green wavelength is 555 nm. Such radiation is called monochromatic because it contains a very narrow range.

Of course, in reality, green is complemented by other colors, so that in the end you can get white.

But since the sensitivity of the human eye is maximum to green, then the lumens are tied to it.

So, a luminous flux of one lumen, just the same, corresponds to a source that emits light with a wavelength of 555 nm. In this case, the power of such a source is 1/683 W.

Why exactly 1/683, and not 1 W for good measure? The value of 1/683 W arose historically. Initially, the main source of light was an ordinary candle, and the radiation of all new lamps and lamps was compared with the light from a candle.

At present, this value of 1/683 is legalized by many international agreements and is accepted everywhere.

Why do we need such a quantity as a luminous flux? With its help, you can easily calculate the illumination of the room.

This directly affects a person's vision.

The difference between illumination and luminous flux

At the same time, many confuse the units of measurement Lumens with Lux. Remember, lux is the measurement of illuminance.

How to clearly explain their difference? Imagine pressure and force. With just a small needle and little force, a 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 1m2 of illuminated area.

Let's say you have a lamp with a luminous flux of 1000 lm. At the bottom of this lamp is a table.

There must be a certain amount of light on the surface of this table so that you can work comfortably. The primary source for illumination standards are 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 done - 500 Lx.

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

From foreign objects nearby. If the table is near a white wall, then there will be more suites, respectively, than from a dark one. Reflection will definitely affect the overall result.

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

Be prepared for mistakes though. But in order to make an initial analysis offhand, the phone will do just fine.

Luminous flux calculation

And how to find out the approximate light flux in lumens, without measuring instruments at all? Here you can use the values ​​of light output and their proportional dependence on the flow.

Light flow- power of light radiation, i.e. visible radiation, estimated by the light sensation that it produces on the human eye. Light output is measured in lumens.

For example, an incandescent lamp (100 W) emits a luminous flux equal to 1350 lm, and a fluorescent lamp LB40 - 3200.

One lumen is equal to the luminous flux emitted by a point isotropic source, with a luminous intensity equal to one candela, into a solid angle, one steradian (1 lm = 1 cd sr).

The total luminous flux created by an isotropic source, with a luminous intensity of one candela, is equal to 4π lumens.

There is another definition: the unit of luminous flux is lumen(lm), equal to the flux emitted by a black body from an area of ​​0.5305 mm 2 at the solidification temperature of platinum (1773 ° C), or 1 candle 1 steradian.

The power of light- spatial density of the luminous flux, equal to the ratio of the luminous flux to the value of the solid angle in which the radiation is evenly distributed. The unit of luminous intensity is the candela.

illumination- surface density of the luminous flux incident on the surface, equal to the ratio of the luminous flux to the size of the illuminated surface, over which it is evenly distributed.

The unit of illumination is lux (lx), equal to the illumination created by a luminous flux of 1 lm, evenly distributed over an area of ​​1 m 2, i.e. equal to 1 lm / 1 m 2.

Brightness- surface density of the luminous intensity in a given direction, equal to the ratio of the luminous intensity to the projection area of ​​the luminous surface onto a plane perpendicular to the same direction.

The unit of brightness is candela per square meter (cd/m2).

Luminosity (lightness)- surface density of the luminous flux emitted by the surface, equal to the ratio of the luminous flux to the area of ​​the luminous surface.

The unit of luminosity is 1 lm/m 2 .

Units of light quantities in the international system of units SI (SI)

Value name	Unit name	Expression via SI units (SI)	Unit designation
			Russian	between- folk
The power of light	candela	cd	cd	cd
Light flow	lumen	cd sr	lm	lm
light energy	lumen second	cd sr s	lm s	lm s
illumination	luxury	cd sr / m 2	OK	lx
Luminosity	lumens per square meter	cd sr / m 2	lm m 2	lm/m2
Brightness	candela per square meter	cd/m2	cd/m2	cd/m2
light exposure	lux second	cd sr s / m 2	lx s	lx s
Radiation energy	joule	kg m 2 / s 2	J	J
Radiation flux, radiation power	watt	kg m 2 / s 3	Tue	W
Light equivalent of the radiation flux	lumens per watt		lm/W	lm/W
Surface radiation flux density	watt per square meter	kg/s 3	W/m2	w/m2
Energy power of light (radiant power)	watt per steradian	kg m2/(s 3 sr)	Tue/Wed	w/sr
Energy Brightness	watt per steradian square meter	kg/(s 3 sr)	W / (sr m 2)	W/(sr m 2)
Energy illumination (irradiance)	watt per square meter	kg/s 3	W/m2	w/m2
Energy luminosity (radiance)	watt per square meter	kg/s 3	W/m2	w/m2

Examples:

ELECTRICAL MANUAL"
Under the general editorship. MPEI professors V.G. Gerasimova and others.
M.: MPEI Publishing House, 1998