And the luminous flux, respectively, and they must be distinguished. The amount of luminous flux characterizes the light source, and the level of illumination characterizes the state of the surface on which the light falls. Lux (Lx) is used to measure illumination, and lumen (Lm) is used to characterize the light source.

You will need
- calculator.

By definition, an illumination of one lux produces a light source with a luminous flux of one lumen if it evenly illuminates a surface of one square meter. Therefore, to convert lumens to suites, use the formula:
Klux = Klumen / Km²
To convert suites to lumens, apply the formula:
Klumen = Klux * Km²,
where:
Klux - illumination (number of lux);
Klumen - the amount of luminous flux (the number of lumens);
Km² - illuminated area (in square meters).


When calculating, keep in mind that the lighting should be uniform. In practice, this means that all points on the surface must be equidistant from the light source. In this case, the light must hit all areas of the surface at the same angle. Also note that the entire luminous flux emitted by the light source must fall on the surface.


If the light source is close in shape to a point one, then uniform illumination can be achieved only on the inner surface of the sphere. However, if the luminaire is sufficiently distant from the illuminated surface, and the surface itself is relatively flat and has a small area, then the illumination can be considered almost uniform. A "striking" example of such a light source can be considered the sun, which, due to its great distance, is almost a point source of light.


Example: In the center of a 10 meter high cubic room, there is a 100 W incandescent lamp.
Question: what will be the illumination of the room ceiling?
Solution: a 100 watt incandescent lamp generates a luminous flux of approximately 1300 lumens (lm). This flow is distributed over six equal surfaces (walls, floor and ceiling) with a total area of ​​600 m². Therefore, their illumination (average) will be: 1300/600 = 2.167 Lx. Accordingly, the average illumination of the ceiling will also be equal to 2.167 Lx.


To solve the inverse problem (determining the luminous flux for a given illumination and surface area), simply multiply the illumination by the area.


However, in practice, the luminous flux created by a light source is not calculated in this way, but is measured using special devices - spherical photometers and photometric goniometers. But since most light sources have standard characteristics, for practical calculations, use the following table:
Incandescent lamp 60 W (220 V) - 500 lm.
Incandescent lamp 100 W (220 V) - 1300 lm.
Fluorescent Lamp 26 W (220 V) - 1600 lm.
Sodium gas discharge lamp(street) - 10,000 ... 20,000 lm.
Low pressure sodium lamps - 200 Lm / W.
LEDs - about 100 Lm / W.
Sun - 3.8 * 10 ^ 28 Lm.


Lm / W is an indicator of the efficiency of a light source. So, for example, a 5 W LED will provide a luminous flux of 500 lm. Which corresponds to a 60W incandescent lamp!

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

How many lumens do you need for 1m 2

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

The calculation (measurement) of the illumination intensity is carried out according to a simple formula (AxBxC) in which:

• A - required illumination according to SNiP standards;
• B is the area of ​​the room (sq. M);
• C - Height coefficient.

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

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

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

Rooms of irregular shape, divide into figures (for example, a square and a triangle), and calculate separately for each.

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

Living room lighting

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

Namely:

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

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

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

Home LED Lamps

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

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

Advantages:

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

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

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

Environmental friendliness is also an important factor. LED lamps do not emit UV radiation and do not create fluctuations in the luminous flux.

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

Illumination rate of office premises: required value

It is not so common for offices with a special emphasis on lighting. These are usually luminous squares with fluorescent shimmer embedded in the ceiling. But light affects both the psychological and the emotional state of a person. With the right lighting, you can achieve high employee productivity all day long.

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

• Russian - illumination level (required scale), recommended in the range of 300 - 400 lux (Lx);
• International standard (European standards) - 500 lux (Lx).

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

The location of the lighting fixtures parallel to the windows is the most correct, this is how the light from the fixtures matches the light from the windows.

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

Lighting for playgrounds: norms

Modern playgrounds, of course, differ from sports ones, but in terms of their functionality they can be equated to each other. A lot of sports equipment is added to the slides, swings and carousels we are used to for the physical development of children. Therefore, competent and effective lighting for playgrounds is a must.

With such characteristics, important parameters must be taken into account for children's playgrounds.

Parameter list:

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

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

The level of color rendering is of great importance when illuminating playgrounds. For the convenience of distinguishing between small and moving objects.

In accordance with the size, for various playgrounds is selected optimal ratio height and location of lighting fixtures. These include console (up to 10 meters high) and local (up to 4 meters high). The power of an individual street lighting device is calculated in accordance with SNiP standards.

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

It is worth considering the aesthetic component, choosing lamps that emphasize the exterior of the site.

How many watts do you need to light a room: converting lumens to watts

There are quite simple answers to the questions - how to determine what kind of lighting should be in a separate room or one room, how to translate suites into watts, how to select and count the required number of lamps.

Let's make a calculation using an example. We need to illuminate the hall with an area of ​​20m 2 with a chandelier with five incandescent light bulbs. What power in watts should I choose the lamps?

For the calculation you will need:

• Illumination degree;
• Area in square meters.

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

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

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

What are illumination standards (video)

It's not just your home or office that needs the right light. It is necessary for a comfortable stay in a hotel, walking down the street, it is important to use it in kindergartens and sales areas. The only difference is purpose and functionality. On the basis of the tests carried out, psychologists have proven that with a well-constructed lighting, not only the psycho-emotional, but also the general condition of a person improves.

Lux and lumens are often confused. These quantities are used to measure illumination and luminous flux, respectively, and must be distinguished. The value of the luminous flux characterizes the light source, and the level of illumination characterizes the state of the surface on which the light falls. Lux (Lx) is used to measure illumination, and lumen (Lm) is used to collate the light source.

You will need

• - calculator.

Instructions

1. By definition, an illumination of one lux produces a light source with a luminous flux of one lumen if it evenly illuminates a surface of one square meter. Consequently, to convert lumens to suites, use the formula: Klux = Klumen / Km? In order to convert suites to lumens, apply the formula: Klumen = Klux * Km?, Where: Klux - illumination (number of lux); Klumen - luminous flux (number of lumens ); Km? - illuminated area (in square meters).

2. When calculating, consider that the lighting should be uniform. In practice, this means that all points on the surface must be equidistant from the light source. In this case, the light must hit all areas of the surface at the same angle. Also note that every luminous flux emitted by the light source must hit the surface.

3. If the light source is close in shape to a point one, then uniform illumination can be achieved only on the inner surface of the sphere. However, if the luminaire is quite distant from the illuminated surface, and the surface itself is relatively flat and has a small area, then the illumination can be considered virtually uniform. A "brilliant" example of a similar light source can be considered a luminary, which, due to its great distance, is an approximately point light source.

4. Example: In the center of a 10 meter high cubic room there is a 100 W incandescent lamp. Question: What will be the illumination of the room's ceiling? Solution: A 100 W incandescent lamp produces a luminous flux of approximately 1300 lumens (lumens). This stream is distributed over six equal surfaces (walls, floor and ceiling) with a total area of ​​600 m2. Consequently, their illumination (average) will be: 1300/600 = 2.167 Lx. Accordingly, the average illumination of the ceiling will also be equal to 2.167 Lx.

5. To solve the inverse problem (determining the luminous flux for a given illumination and surface area), easily multiply the illumination by the area.

6. However, in practice, the luminous flux created by a light source is not calculated in this way, but is measured with the support of special devices - spherical photometers and photometric goniometers. But because many light sources have typical collations, use the following table for actual calculations: 60 W incandescent lamp (220 V) - 500 lm. 100 W incandescent lamp (220 V) - 1300 lm. 26 W fluorescent lamp (220 V) - 1600 lm. Sodium gas-discharge lamp (outdoor) - 10,000 ... 20,000 lm. Low pressure sodium lamps - 200 Lm / W. LEDs - about 100 Lm / W. Luminosity - 3.8 * 10 ^ 28 Lm.

7. Lm / W is an indicator of the effectiveness of the light source. So, say, a 5 W LED will provide a luminous flux of 500 lm. Which corresponds to a 60W incandescent lamp!

When calculating the amount of consumed electricity, it is customary to use the representation “kilowatt- clock". This value is the actual consumption of electricity by a device with a power of N kilowatts for the number of hours X.

Instructions

1. First, figure out which value you need to take into account. The fact is that often when calculating electricity, the representation of kilowatt- clock and kilowatts are confused. True, kilowatts is the power (that is, the number of energy consumed by the device), and the kilowatt-hour is the number of time consumed per hour.

2. Please note that the energy consumption on the electricity meter is indicated in kilowatts. To convert them to watts, multiply the number of kilowatts by one 1000. Thus, 1 kilowatt * 1000 = 1000 watts.

3. Because watt- clock or kilowatt clock- this is the number of watts for a certain time interval, for calculations you need to know for what time interval the figure was taken. Divide the number of watt-hours by the number of hours that are being calculated.

4. Let's say you know that for a month (30 days) the consumption of electricity by metering devices is 72 kilowatt / hour. We multiply this figure by 1000. In order to get the number of watts. 68.4 * 1000 = 68400 watt / hour. Now let's divide the resulting figure by 720. That is how many hours in one month (30 * 24 = 720). 68400/720 = 95 watts. It turns out that one electric lamp with a power of 95 watts was continuously burning for a month.

5. Remember that this data will be of an approximate average character if you are making a general calculation. It is unrealistic to single out one specific electrical appliance. This formula also does not consider energy losses. To calculate the power of watts for a separate device, you need to connect it to the network in a single copy, leaving it on for an hour. The resulting figure will be the desired value. Let's say if an electric iron was connected to the network. Having consumed 1,500 watts / hour in one hour, the power consumption of this device will be exactly 1,500 watts.

Instructions

According to the definition, an illumination of one lux creates a luminous flux of one lumen if it evenly illuminates a surface of one square meter. Therefore, to convert lumens to suites, use the formula:

Klux = Klumen / Km²

To convert suites to lumens, apply the formula:

Klumen = Klux * Km²,

where:
Klux - illumination (number of lux);
Klumen - value (amount of lumens);
Km² - illuminated area (in square meters).

When calculating, keep in mind that the lighting should be uniform. In practice, it is that all points on the surface must be equidistant from the light source. In this case, the light must hit all areas of the surface at the same angle. Also note that the entire flux emitted by the light source must hit the surface.

If the light source is close in shape to a point one, then uniform illumination can be achieved only on the inner surface of the sphere. However, if the luminaire is sufficiently distant from the illuminated surface, and the surface itself is relatively flat and has a small area, then the illumination can be considered almost uniform. A "striking" example of such a light source can be considered, which, due to its great distance, is an almost point light source.

Example: In the center of a 10 meter cubic room, there is a 100 W incandescent lamp.

Question: what will be the illumination of the room ceiling?

Solution: a 100 watt incandescent lamp generates a flux of approximately 1300 lumens (lm). This stream is distributed over six equal surfaces (walls, floor and) with a total area of ​​600 m². Therefore, their illumination (average) will be: 1300/600 = 2.167 Lx. Accordingly, the average illumination of the ceiling will also be equal to 2.167 Lx.

However, in practice, the luminous flux created by a light source is not calculated in this way, but with the help of special devices - spherical photometers and photometric goniometers. But since most light sources have standard characteristics, for practical calculations, use the following table:

Incandescent lamp 60 W (220 V) - 500 lm.
Incandescent lamp 100 W (220 V) - 1300 lm.
Fluorescent lamp 26 W (220 V) - 1600 lm.
Sodium gas discharge lamp (outdoor) - 10,000 ... 20,000 lm.
Low pressure sodium lamps - 200 Lm / W.
LEDs - about 100 Lm / W.
Sun - 3.8 * 10 ^ 28 Lm.

Lm / W is an indicator of the efficiency of a light source. So, for example, a 5 W LED will provide a luminous flux of 500 lm. Which corresponds to a 60W incandescent lamp!

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1 lux [lx] = 1.46412884333821E-07 watts per sq. cm (at 555 nm) [W / cm² (555 nm)]

Initial value

Converted value

lux meter-candela centimeter-candela foot-candela phot nox candela-steradian per sq. meter lumens per sq. meter lumens per sq. centimeter lumens per sq. foot watt per sq. cm (at 555 nm)

Mass concentration in solution

More about illumination

General information

Illuminance is a luminous quantity that determines the amount of light that hits a given area of ​​the body's surface. It depends on the wavelength of light, since the human eye perceives the brightness of light waves of different lengths, that is, different colors, in different ways. Illumination is calculated separately for waves of different wavelengths, since people perceive light with a wavelength of 550 nanometers (green), and colors that are nearby in the spectrum (yellow and orange), as the brightest. Light generated by longer or shorter wavelengths (violet, blue, red) is perceived as darker. Illumination is often associated with the concept of brightness.

Illumination is inversely proportional to the area over which the light falls. That is, when illuminating the surface with the same lamp, the illumination of a larger area will be less than the illumination of a smaller area.

Difference between brightness and illumination

Brightness Illumination

In Russian, the word "brightness" has two meanings. Brightness can mean a physical quantity, that is, a characteristic of luminous bodies equal to the ratio of the intensity of light in a certain direction to the projection area of ​​the luminous surface onto a plane perpendicular to this direction. It can also define a more subjective concept of overall brightness, which depends on many factors, such as the characteristics of the eyes of the person who is looking at this light, or the amount of light in the environment. The less light around you, the brighter the light source appears. In order not to confuse these two concepts with illumination, it is worth remembering that:

brightness characterizes light, reflected from the surface of a luminous body or sent by this surface;

illumination characterizes falling light onto the illuminated surface.

In astronomy, brightness characterizes both the emitting (stars) and reflective (planets) ability of the surface of celestial bodies and is measured on the photometric scale of stellar brightness. Moreover, the brighter the star, the lower the value of its photometric brightness. The brightest stars have negative stellar brightness.

Units

Illumination is most often measured in SI units. suites... One lux equals one lumen per square meter. Those who prefer imperial units to metric units use to measure illumination foot candela... It is often used in photography and cinema, as well as in some other fields. The foot is used in the name because one foot-candela denotes the illumination of one candela of a surface of one square foot, which is measured at a distance of one foot (a little over 30 cm).

Photometer

A photometer is a device that measures illumination. Typically, light is sent to a photo detector, converted into an electrical signal, and measured. Sometimes there are photometers that work on a different principle. Most photometers provide lux information, although other units are sometimes used. Photometers called exposure meters help photographers and operators to determine shutter speed and aperture. In addition, photometers are used to determine safe illumination in the workplace, in crop production, in museums, and in many other industries where it is necessary to know and maintain a certain illumination.

Illumination and safety in the workplace

Working in a dark room can lead to visual impairment, depression, and other physiological and psychological problems. That is why many labor protection rules include requirements for minimum safe illumination of the workplace. Measurements are usually carried out with a photometer, which gives the final result depending on the area of ​​propagation of the light. This is necessary in order to provide sufficient illumination throughout the room.

Illumination in photography and video shooting

Most modern cameras have built-in exposure meters to simplify the work of the photographer or operator. A light meter is necessary so that the photographer or operator can determine how much light needs to be transmitted onto the film or photomatrix, depending on the illumination of the object being shot. Illumination in lux is converted by the exposure meter into possible combinations of shutter speed and aperture, which are then selected manually or automatically, depending on how the camera is configured. Usually the combinations suggested will depend on the settings in the camera and what the photographer or cameraman wants to portray. In the studio and on location, an external or in-camera light meter is often used to determine if the light sources being used are providing sufficient lighting.

For getting good photos or video material in poor lighting conditions, a sufficient amount of light must enter the film or sensor. This is not difficult to achieve with a camera - you just need to set the correct exposure. The situation with video cameras is more complicated. For high quality video, you usually need to install additional lighting, otherwise the video will be too dark or with a lot of digital noise. This is not always possible. Some camcorders are specially designed for shooting in low light conditions.

Cameras designed for shooting in low light conditions

There are two types of cameras for shooting in low light conditions: some use more optics than high level while others have more advanced electronics. The optics let more light into the lens, and the electronics are better at processing even the smallest light that enters the camera. Typically, it is with electronics that the problems and side effects described below are associated. High-aperture optics allow you to shoot video of higher quality, but its disadvantages are additional weight due to a large number glass and a significantly higher price.

In addition, the quality of shooting is affected by the single-matrix or three-matrix photo matrix installed in video and photo cameras. In a three-matrix matrix, all incoming light is divided by a prism into three colors - red, green and blue. Image quality in dark conditions is better in three-matrix cameras than in single-matrix cameras, since less light is scattered when passing through a prism than when it is processed by a filter in a single-matrix camera.

There are two main types of photo matrices - charge-coupled devices (CCDs) and made on the basis of CMOS technology (complementary metal oxide semiconductor). In the first, a sensor is usually installed, which receives light, and a processor that processes the image. In CMOS sensors, the sensor and the processor are usually combined. In low light conditions, CCD cameras usually produce better image quality, and the advantage of CMOS sensors is that they are cheaper and consume less power.

The size of the image sensor also affects the image quality. If shooting takes place with a small amount of light, then the larger the matrix, the better quality image, and the smaller the matrix, the more problems with the image - digital noise appears on it. Larger sensors are installed in more expensive cameras, and they require more powerful (and, as a result, heavier) optics. Cameras with such matrices allow you to shoot professional video. For example, recently a number of films have appeared completely shot on cameras such as the Canon 5D Mark II or Mark III, which have a matrix size of 24 x 36 mm.

Manufacturers usually indicate in what minimum conditions the camera can work, for example, with an illumination of 2 lux or more. This information is not standardized, that is, the manufacturer decides for himself which video is considered to be of high quality. Sometimes two cameras with the same minimum illumination will give different quality shooting. The EIA (Electronic Industries Association) in the United States has proposed a standardized system for determining the sensitivity of cameras, but so far it is used only by a few manufacturers and is not universally adopted. Therefore, often, in order to compare two cameras with the same light characteristics, you need to try them in action.

On the this moment any camera, even one designed for low light conditions, can produce poor quality images with high graininess and afterglow. To solve some of these problems, it is possible to take the following steps:

• Shoot on a tripod;
• Work in manual mode;
• Do not use variable focal length mode, but instead move the camera as close to the subject as possible;
• Do not use auto focus and auto ISO selection - higher ISO values ​​increase noise;
• Shoot with a shutter speed of 1/30;
• Use diffused light;
• If it is not possible to install additional lighting, then use all possible light around, such as street lamps and moonlight.

Despite the lack of standardization about the sensitivity of cameras to light, for night photography it is still better to choose a camera that says it works at 2 lux or lower. Also keep in mind that even though the camera is really good at shooting in dark conditions, its Lux sensitivity to light is the sensitivity to light directed at an object, but the camera actually receives light reflected from the object. When reflected, part of the light is scattered, and the further the camera is from the object, the less light enters the lens, which degrades the quality of shooting.

Exposition number

Exposition number(English Exposure Value, EV) - an integer characterizing possible combinations excerpts and diaphragm in a photo, film or video camera. All combinations of shutter speed and aperture, in which the same amount of light falls on the film or the photosensitive matrix, have the same exposure number.

Several combinations of shutter speed and aperture in the camera at the same exposure number allow you to get approximately the same image density. However, the images will be different. This is due to the fact that at different aperture values, the depth of field will be different; at different shutter speeds, the image on the film or matrix will remain for different times, as a result of which it will be blurred to varying degrees or not at all. For example, combinations of f / 22 - 1/30 and f / 2.8 - 1/2000 are characterized by the same exposure number, but the first image will have a greater depth of field and may be blurry, and the second will have a shallow depth of field and, quite possibly will not be blurry at all.

Higher EV values ​​are used when the subject is better lit. For example, an exposure value (at ISO 100) EV100 = 13 can be used when shooting a landscape if the sky is cloudy, and EV100 = –4 is suitable for shooting a bright aurora.

By definition,

EV = log 2 ( N 2 /t)

2 EV = N 2 /t, (1)

where
• N- f-number (for example: 2; 2.8; 4; 5.6, etc.)
• t- shutter speed in seconds (for example: 30, 4, 2, 1, 1/2, 1/4, 1/30, 1/100, etc.)

For example, for a combination of f / 2 and 1/30, the exposure value is

EV = log 2 (2 2 / (1/30)) = log 2 (2 2 × 30) = 6.9 ≈ 7.

This number can be used for night scenes and illuminated shop windows. A combination of f / 5.6 with a shutter speed of 1/250 gives an exposure value

EV = log 2 (5.6 2 / (1/250)) = log 2 (5.6 2 × 250) = log 2 (7840) = 12.93 ≈ 13,

which can be used to capture a landscape with a cloudy sky and no shadows.

It should be noted that the argument of the logarithmic function must be dimensionless. In determining the exposure number EV, the dimension of the denominator in formula (1) is ignored and only the numerical value of the shutter speed in seconds is used.

The relationship of the exposure number with the brightness and illumination of the subject

Determining the exposure by the brightness of the light reflected from the subject

When using exposure meters or lux meters that measure the light reflected from the subject, shutter speed and aperture are related to the brightness of the subject as follows:

N 2 /t = LS/K (2)

• N- f-number;
• t- exposure in seconds;
• L- average scene brightness in candelas per square meter (cd / m²);
• S- arithmetic value of photosensitivity (100, 200, 400, etc.);
• K- calibration factor of the exposure meter or lux meter for reflected light; Canon and Nikon use K = 12.5.

From equations (1) and (2) we obtain the exposure number

EV = log 2 ( LS/K)

2 EV = LS/K

At K= 12.5 and ISO 100, we have the following equation for brightness:

2 EV = 100 L/12.5 = 8L

L= 2 EV / 8 = 2 EV / 2 3 = 2 EV – 3.

Illumination and museum exhibits

The rate at which decay, fade, and otherwise deteriorate museum exhibits, depends on their illumination and on the strength of the light sources. Museum staff measure the illumination of exhibits to make sure that a safe amount of light is entering the exhibits, and also to provide enough light for visitors to get a good look at the exhibit. Illumination can be measured with a photometer, but in many cases this is not easy, since it must be as close to the exhibit as possible, and for this it is often necessary to remove protective glass and turn off the alarm, as well as obtain permission to do so. To facilitate the task, museum workers often use cameras as photometers. Of course this is not a substitute accurate measurements in a situation where a problem is found with the amount of light that enters the exhibit. But in order to check whether a more serious check with a photometer is needed, a camera is enough.

The exposure is determined by the camera based on the light readings, and knowing the exposure, you can find the light with a few simple calculations. In this case, museum staff use either a formula or a table with the conversion of exposure into light units. During calculations, do not forget that the camera absorbs part of the light, and take this into account in the final result.

Illumination in other areas of activity

Gardeners and plant breeders know that plants need light for photosynthesis, and they know how much light each plant needs. They measure light in greenhouses, orchards and vegetable gardens to make sure each plant is getting enough light. Some people use photometers for this.

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