In order for any production task to be completed quickly and efficiently, the lighting of the specialist’s workplace must be properly organized. For this purpose, lamps with certain photometric indicators are selected.

Lighting in the workplace is determined by various physical quantities, the main one of which is illumination. Its indicators are calculated for the workplace of any specialist and are regulated by the relevant SNiPs.

Illumination is a characteristic that is defined as the luminous flux per unit area.

Luminous flux (F)

This physical parameter is defined as the power of visible radiation from a source or the light energy that is emitted by a lamp per unit time.

At the same time, light energy is energy that spreads in all directions and causes visual sensations. Each person has different visual sensations to the same radiation sources, so averaged indicators are taken for calculations.

In physics, the formula is used for calculation:

Ф = W/t, where:

• W – energy emitted by the source, measured in watts,
• t – operating time of the device in seconds.

It is also a quantity that characterizes the amount of light emitted by a lighting fixture in all directions.

Thus, the second calculation formula looks like:

Ф = I w, where:

• I – luminous intensity, measured in candelas,
• w – solid angle, calculated in steradians.

Lumen

The unit of measurement for luminous flux is lumen.

In order to determine which source is more profitable to purchase, let’s first consider what a lumen is.

The word lumen in Latin means light.

A lumen is defined as the luminous flux that is emitted by a point source having a luminous intensity of 1 candela per solid angle equal to 1 steradian:

1lm = 1W / 1s.

On the other side,The unit of measurement lumen (lm) can be found as:

1 lm = 1 cd · 1 sr.

If the solid angle is equal to 4π radians and the luminous intensity is 1 cd, then in this case we speak of the total luminous flux, which is equal to 4π lm or 4 · 3.14 lm.

It was calculated that this indicator for solar radiation corresponds to 8 lm, and for the starry sky - only 0.000000001 lm.

For any artificial light source there are tables for calculating this photometric parameter.

In lighting engineering, derived quantities are used, which are formed using standard prefixes of the international SI system, for example:

• 1 klm = 103 lm or 1 klm = 103 lm;
• 1 Mlm = 106 lm;
• 1 lm = 10-3 lm;
• 1 µlm = 10-6 lm.

Measuring instruments

To measure photometric quantities, industry uses special devices called spherical photometers and goniophotometers. They allow you to determine both the luminous flux and the intensity of light from various lamps.

Photometers are either visual or objective.

The principle of operation of visual devices is based on the ability of the eye to determine the same brightness of illumination of two compared surfaces illuminated with the same color.

Currently, objective electric photometers are popular, which allow measuring light parameters not only in the visible zone, but also beyond it.

Goniophotometers allow you to obtain data on the amount of luminous flux, luminous intensity, as well as indicators of other photometric quantities, for example, brightness, illumination distribution, etc.

Recommendations for organizing proper workplace lighting

When lighting workplaces, two types of sources are used: artificial and natural.

Artificial ones are devices with lamps of various types: fluorescent, incandescent, LED, etc.

For each type of lamp, there are tables indicating the number of lumens emitted by a given lamp.

This value is indicated on the product packaging, so when purchasing, be sure to select a light bulb based on the information posted by the manufacturer on the box. The packaging of the lamp indicates the total luminous flux, which includes diffused light.

Attention! When purchasing a lamp, it is important to remember that this indicator does not fully reflect its brightness, since it can be increased through the use of a system of reflectors, lenses and mirrors located in the device.

Selection of electric lamps

Before purchasing light bulbs, you must first choose which devices you need to create the right lighting for your workplace. If the room is rectangular, then the required number of lumens is calculated as follows: you need to multiply the indicators of the illumination standard of the object (determined according to SNiP), the area of ​​the room and the coefficient depending on the height of the ceiling of the room.

Luminous flux- the power of light radiation, i.e. visible radiation, assessed by the light sensation that it produces on the human eye. Luminous flux is measured in lumens.

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

One lumen equal to the luminous flux emitted by a point isotropic source, with a luminous intensity equal to one candela, per solid angle, equal to 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 an absolutely 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 uniformly distributed. The unit of luminous intensity is the candela.

Illumination- surface density of the light flux incident on the surface, equal to the ratio of the light 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, uniformly distributed over an area of ​​1 m2, i.e. equal to 1 lm/1 m2.

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

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

Luminosity (luminosity)- 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/m2.

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

Examples:

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

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Initial value

Converted value

candela candle (German) candle (UK) decimal candle pentane candle pentane candle (10 SW) Hefner candle Carcel unit candle decimal (French) lumen/steradian candle (international)

More about the power of light

General information

Luminous intensity is the power of the luminous flux within a certain solid angle. That is, the intensity 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 luminous intensity decreases or increases as the solid angle changes, although sometimes this value is the same for any angle if the source distributes the light evenly. Luminous intensity is a physical property of light. In this way, it differs from brightness, since in many cases, when they talk about brightness, they mean a subjective sensation, and not a physical quantity. Also, brightness does not depend on the solid angle, but is perceived in the general space. The same source with a constant luminous intensity can be perceived by people as light of different brightness, since this perception depends on environmental conditions and on the individual perception of each person. Also, the brightness of two sources with the same luminous intensity may be perceived differently, especially if one produces diffuse light and the other directed light. In this case, the directional source will appear brighter, even though the luminous intensity of both sources is the same.

Luminous 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. The sensitivity of people to light depends on the wavelength and is expressed by the function of relative spectral luminous efficiency. The intensity of the 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 of longer or shorter wavelengths.

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

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

In the illustration, light emitted by two sources, red and yellow, covers an equal area. Yellow light is diffused, like candle light. Its strength is approximately 100 cd, regardless of direction. Red is the opposite, directional. In the direction of 0°, where the radiation is maximum, its strength is 225 cd, but this value quickly decreases with deviations 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 light intensity in museum spaces to determine the optimal conditions for visitors to view the works on display, while at the same time providing gentle light that causes as little damage as possible to museum exhibits. 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 made from these materials, so the light in the exhibition halls poses a great danger. The stronger the light intensity, the more museum exhibits deteriorate. In addition to destruction, light also discolors or yellows cellulose-containing materials such as paper and fabrics. Sometimes the paper or canvas on which paintings are painted deteriorates and breaks down faster than paint. This is especially problematic since the paint on a painting is easier to restore than the base.

The damage caused to museum exhibits depends on the wavelength of light. For example, light in the orange spectrum is the least harmful, and blue light is the most dangerous. That is, light with longer wavelengths is safer than light with shorter wavelengths. Many museums use this information and control not only the total amount of light, but also limit blue light using light orange filters. At the same time, they try to choose filters that are so light that, although they filter out 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 intensity of light, how quickly the materials from which they are made will degrade. Long-term storage in museum spaces requires not only low lighting, but also low humidity and low oxygen levels, at least within display cases.

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

Luminous intensity of lamps

The properties of lamps are usually described using luminous intensity, which differs from the luminous flux - a value that determines the total amount of light and shows how bright this source is in general. It is convenient to use luminous intensity to determine the luminous properties of lamps, for example, LED lamps. When purchasing them, information about the light intensity helps determine with what strength and in what direction the light will spread, and whether such a lamp is suitable for the buyer.

Light intensity distribution

In addition to the luminous intensity itself, luminous intensity distribution curves help to understand how the lamp will behave. Such diagrams of the angular distribution of light intensity are closed curves on a plane or in space, depending on the symmetry of the lamp. They cover the entire range of light propagation of this lamp. The diagram shows the magnitude of the light intensity depending on the direction of its measurement. The graph is usually plotted in either a polar or rectangular coordinate system, depending on the light source for which the graph is being plotted. It is often placed on lamp packaging to help the buyer imagine how the lamp will perform. This information is important for designers and lighting engineers, especially those who work in the field of cinema, theater, and the organization of exhibitions and performances. Luminous intensity distribution also affects driving safety, which is why engineers designing vehicle lighting use luminous intensity distribution curves. They must comply with strict regulations governing the distribution of light intensity in headlights 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 candelas, 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 intensity and distribution of light intensity

Light intensity 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 light intensity from different angles. Sometimes, instead of a mirror, the light source itself moves. Typically these devices are large, with a distance of up to 25 meters between the lamp and the sensor that measures light intensity. 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 measurement. When purchasing a goniophotometer, the decisive factors, among other factors, are its price, size, power, and the maximum size of the light source that it can measure.

Half Brightness Angle

Half-brightness angle, sometimes also called glow angle, is one of the quantities that helps describe a light source. This angle indicates how directional or diffuse the light source is. It is defined as the angle of the light cone at which the source's luminous intensity is equal to half 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 100 cd. The angle at which the luminous intensity of the beam reaches 100 cd., that is, the angle of half brightness, is equal to 60 + 60 = 120 ° on the graph (half the angle is depicted 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 than 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 advantages to both wide and narrow half-brightness angles, and which one should be preferred depends on the application of the light source. For example, for scuba diving, you should choose a flashlight with a narrow angle of half brightness if there is good visibility in the water. If visibility is poor, then there is no point in using such a flashlight, since it only wastes energy. In this case, a flashlight with a wide angle of half brightness, which diffuses the light well, is a better choice. 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 can be manually adjusted to half brightness, which is useful since divers can't always predict what the visibility will be like where they're diving.

Anyone who begins to study the characteristics of lamps and individual types of lamps is sure to encounter 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 related to each other, 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 for the hallway, kitchen, or living room was its power. No one has ever thought to ask in a store about some lumens or candelas.

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

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

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

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

• from source power

Here is a table of this dependence for LED lamps:

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

Incandescent light bulbFluorescent lamp Halogen DNA DRL

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

It’s just that some of them have gone further and learned to extract more lumens from one watt than others.

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

Beautifully written on the box:

• power 9W

• light output 1000lm

• analogue of incandescent lamp 100W

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

But with this power, you won't get anywhere near the light you used to have. You will begin to swear at LEDs and their imperfect technologies. But the problem turns out to be an unscrupulous manufacturer and his product.

• on efficiency

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

It turns out that this is a 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 the color green. For example, if you take two lamps with the same power of blue and green, then for all of us the green one will seem brighter.

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, the lumens were tied to it.

So, a luminous flux of one lumen exactly 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 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.

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

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

This directly affects a person's vision.

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.

Calculation of luminous flux

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