Suites and lumens. How to choose a lamp

Ten years ago, choosing the right light bulb was easier, because the incandescent lamps had the marking with the maximum power. Currently, more and more popular are new LED lamps. To choose a product of the right capacity in the modern era of lighting is more difficult, because LED lamps, compact fluorescent and other energy-saving lamps have completely changed the power values. Now navigate the watts will not be entirely correct, and not always possible. If in an ordinary store a specialist can still help you find the right bulb, then when you make a purchase through the Internet, you are unlikely to find a watt in the description of this light bulb.

What is the light flux?

Watts means the amount of energy consumed. For example, more energy uses a 100 watt bulb than a 60 watt bulb. This value shows how much energy will be wasted - it does not in any way indicate the amount of light rays that a lamp gives. How much light you get from the light bulb shows 1 lumen.

Lumen is a unit of measurement   light flux in the system of calculi. The brighter the light bulb, the greater this value will be. For example, a conventional incandescent lamp with a power of 40 W has a luminous flux of 300 lumens. Translate lumens into watts is not as easy as it sounds.

On the packaging of each product must be information on how much light this product gives. When electricity is converted into light rays, some of it is lost and therefore large values ​​are not achieved. It can be seen that this indicator of incandescent lamps is 12 lumens to one watt, whereas fluorescent lamps give 60 lumens to one watt. LED lamps have maximum illumination with minimum energy consumption - up to 90 lumens per watt.

Using this approach, it is not always possible to get the right results, because even light bulbs of the same type with the same power can have a different ratio of light flux to energy costs, and the difference can be quite significant. Below is a table that allows you to translate watts into lumens for a lamp when first used. With its help you can easily find out how many lumens in an incandescent lamp, for example.

From the table it follows that the LED lamp with a luminous flux of 600 lm is not equivalent to a 60 W incandescent lamp, and 1,000 lm is not equivalent to a 100 W incandescent lamp.

Parameters that determine the indicator of the luminous flux and its calculation

A ray consists of a stream of particles - photons. When these particles fall into the person's eyes, certain visual sensations arise. The more photons hit the retina in a certain period of time, the more illuminated the subject seems to us. Thus, the bulbs emit a light flux of photons, which, getting into the eyes, allow us to see objects well in front of us.

Unfortunately, the longer the bulb is used, the less brightness it can give. Illumination can also be diminished by the lamp itself, because often the losses depend on the quality of the lamp material. The largest losses of light flux are observed in gas-discharge sources, in luminescent lamps these losses can be 20-30%, for incandescent lamps - 10-15%. LED lamps have the greatest light output - light losses are less than 5%.

To translate the luminous flux of a lamp into lumens, use the average luminous efficiencies:

• for diode products multiply the power by 80-90 lm / watt for bulbs with a matt bulb and get a light flux;
• for diode filamentous (transparent products with yellow stripes) multiply the power consumption by 100 lm / w;
• fluorescent energy saving lamps multiply by 60 lm / w;
• for the lamp DNTT this value will be 66 lm / watt for 70W; 74 lm / watt for 100W, 150W, 250W; 88 lm / W at 400W;
• for an arc mercury lamp, the multiplier will be 58 lm / vol;
• a 100 W incandescent lamp gives a current of about 1,200 lumens. If the power is reduced to 40 W, the flow will reach 400 lm. But a 60-watt bulb has an indicator of about 800 lumens.

If you need to accurately determine the light flux, you need a luxometer. Using it, you can calculate , which luminous flux will be at the selected points of the room according to a known technique.

One suite corresponds to a certain luminous flux that hits an illuminated surface of one square meter. Determine the approximate value of the light flux produced by a particular source, using the formula:

Φ = E × S,
  where S is the area of ​​all surfaces of the room you are researching (in square meters), and E is the illumination (in lux).

So if the surface area is 75 square meters. meters, and the illumination is 40 lux, the luminous flux is 3,000 lumens. To calculate the luminous flux accurately, many other spatial factors will have to be taken into account.

If you are correct, in all respects, you will select an LED lamp, if you follow all the requirements of the manufacturer, it will be guaranteed to last for many years. Currently, the least energy-intensive and providing the most illumination of products are not cheap, but eventually they will be available to all consumers.

One of the main questions that confronts you when choosing a lamp is its brightness. Everyone knows what incandescent lamp to put, screw in a chandelier or lamp to make it light. And what kind of luminescent is needed? Or LED? For a long time for the vast majority of people, the main criterion in choosing a lamp was its power. All approximately represent, what will be a difference in brightness at an incandescent lamp, capacity in 100 Watt, 75 Watt, 40 Watt, etc. Recently, the market of home lighting is displaying more and more different energy-saving products that consume fewer times incandescent lamps. Understand what kind of lamp you need, it becomes not so simple.

Let's try to figure it out. Most manufacturers of light in the Russian market write power equivalents on their lamps. Let us assume that 20 Watt luminescent is equivalent to 40 Watt incandescent, or 9 Watt LED is equivalent to 75 Watt filament. Those. simply speaking, they write what light flux would have had a similar incandescent lamp. For many (and this is obvious), there is confusion.

The luminous flux is measured in lumens. Wikipedia writes: "One lumen (designation: lm, lm) is equal to the light flux emitted by a point isotropic source, with a light intensity equal to one candle, into a solid angle of one steradian (1 lm = 1 cd). The total luminous flux produced by an isotropic source, with a light intensity of one candela, is equal to the lumens. "Is it not clear? It can be explained more simply. Lumen shows how much light you get from a light bulb. The more lumens, the brighter the light. A smaller number of lumens gives less light. Here is the ratio to incandescent lamps:

Accordingly, if you want a brighter something to light - take products that have more Lumens! If the brightness is needed a little, then vice versa! However, there is one nuance. Lumen is the total luminous flux from the source. However, since the lumen does not take into account the focusing efficiency of the reflector or lens, it is not a direct parameter to estimate the luminosity or useful performance of a lamp. A wide light beam can have the same lumens index as a narrow focus beam. Lumens can not be used to determine the intensity of a beam, because the lumen score includes all the scattered and useless light. The units of measurement of illumination are Luxs.

1 The suite is equal to the illumination of a surface area of ​​1 m2, with a light flux of radiation incident on it equal to 1 lumens. If you collect 100 lumens and project them into an area of ​​1 m2, then the illumination of this area will be 100 lux. If the same 100 lumens are sent to 10 m2, then the illumination is 10 lux.

For example, on a full moon, with a clear sky, in our temperate latitudes, the number of suites will be 0.25-0.33. If you happen to visit tropical countries, then you probably noticed how it can be clear at night. So, with the full moon in the tropics, the average number of suites can already be reached 0.9 - 1.1 lux!

Practical Germans have developed a very useful table of optimal lighting in suites for different occasions of life. Lumen, lux, candela, watts, power, luminous flux, luminous intensity. It is not always easy to understand what these meanings mean. We will help you with this, below you will find an article in which a simple language is written in both cases, all these values ​​are interrelated.

The table before you:

Lumen (lm, lm) is the unit of measurement of the luminous flux in SI.

One lumen is equal to the light flux emitted by the point isotropic source, with a luminous intensity equal to one candle, into a solid angle of one steradian (1 lm = 1 kd? Cp). The total luminous flux generated by an isotropic source, with a light intensity of one candela, is 4? lumens.

A conventional incandescent lamp with a power of 100 W creates a luminous flux equal to about 1300 lumens. A compact fluorescent fluorescent lamp of 26 W produces a luminous flux of approximately 1600 lm. The luminous flux of the sun is 3.8? 1028 lm.

Lumen - Full luminous flux from the source. However, this measurement usually does not take into account the focusing efficiency of the reflector or lens and therefore is not a direct parameter to estimate the brightness or useful performance of the beam of the flashlight. A wide beam of light can have the same lumens index as a narrow-beam one. Lumens can not be used to determine the intensity of a beam, because the score in lumens includes all the scattered, useless light.

Suite   (designation: лк, lx) - unit of measurement of illumination in SI system.

Lux is equal to the illumination of a surface area of ​​1 m? with a light flux of radiation incident on it equal to 1 lumens.

100 lumens were collected and projected onto a 1-meter square area.

Illumination area is 100 lux.

The same 100 lumens aimed at 10 square meters will give an illumination of 10 lux.

Candela   (designation: cd, cd) is one of the seven basic units of the SI system, equal to the intensity of light emitted in a given direction by a source of monochromatic radiation with a frequency of 540 · 1012 hertz, whose luminous intensity in this direction is (1/683) W / .

The selected frequency corresponds to the green color. The human eye has the greatest sensitivity in this region of the spectrum. If the radiation has a different frequency, then a higher energy intensity is required to achieve the same intensity.

Previously candela was defined as the intensity of light emitted by a black body perpendicular to a surface of 1/60 cm? at the melting point of platinum (2042.5 K). In the modern definition, the coefficient 1/683 is chosen so that the new definition corresponds to the old one.

The intensity of light emitted by a candle is approximately equal to one candela (candela candle), so earlier this unit of measurement was called a "candle", now this name is obsolete and is not used.

Illuminance is a light quantity that determines the amount of light that hits a certain surface area of ​​the body. It depends on the wavelength of light, because the human eye perceives the brightness of light waves of different lengths, that is, different colors, in different ways. Illuminance is calculated separately for waves of different lengths, because people perceive light with a wavelength of 550 nanometers (green), and colors that are near in the spectrum (yellow and orange), as the brightest. The light formed by longer or shorter waves (violet, blue, red) is perceived as darker. Often illumination is associated with the concept of brightness.

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

The difference between brightness and light

Brightness Illumination

In the Russian language 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 area of ​​the projection of the luminous surface on a plane perpendicular to this direction. It can also define a more subjective concept of overall brightness, which depends on many factors, for example, the characteristics of the eyes of one who looks at this light, or the amount of light in the environment. The less light around, the brighter the light source appears. In order not to confuse these two concepts with illumination it is worth remembering that:

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

illumination   characterizes falling   on the illuminated surface light.

In astronomy, brightness characterizes both the radiating (stars) and reflecting (planets) ability of the surface of celestial bodies and is measured from the photometric scale of stellar brightness. Moreover, the brighter the star, the smaller its photometric brightness. The brightest stars have a negative magnitude of stellar brightness.

Units

Illuminance is most often measured in SI units suites. One lux is equal to one lumen per square meter. Those who prefer imperial units to imperial ones are used to measure illumination foot candela. Often it is used in photography and cinema, as well as in some other areas. The foot in the name is used because one foot candela means the illumination of one candela of the surface in one square foot, which is measured at a distance of one foot (just over 30 cm).

Photometer

A photometer is a device that measures illumination. Usually, light enters the photodetector, it is converted into an electrical signal and measured. Sometimes there are photometers that work on a different principle. Most of the photometers show information about the illumination in the suites, although other units are sometimes used. Photometers, called exposure meters, help photographers and cameramen determine exposure and aperture. In addition, photometers are used to determine safe lighting in the workplace, in plant growing, 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 threatens to impair vision, depression and other physiological and psychological problems. That is why many labor protection rules include requirements for minimum safe workplace illumination. Measurements are usually made by a photometer, which produces the final result depending on the area of ​​light propagation. This is necessary in order to provide sufficient illumination throughout the room.

Illumination in photography and video

Most modern cameras have built-in exposure meters, which simplify the work of a photographer or an operator. An exponometer is necessary for a photographer or an operator to determine how much light should be passed on a film or a photomatrix, depending on the illumination of the object being photographed. Illumination in lux is converted by an 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 proposed combinations depend on the settings in the camera, as well as on what the photographer or operator wants to portray. In the studio and on the set, an external or built-in exposure meter is often used to determine if enough light sources are provided by the light sources used.

To obtain good photographs or video material in conditions of poor lighting, a sufficient amount of light must fall on the film or photomatrix. This is not difficult to achieve with a camera - you just need to install the correct exposure. With video cameras, things are more complicated. For high-quality video, you usually need to install additional lighting, otherwise the video will be too dark or with strong digital noise. This is not always possible. Some camcorders specifically 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 optics of a higher level, and in others - more sophisticated electronics. The optic transmits more light into the lens, and the electronics better handle even that small light that gets into the camera. Usually it is with electronics that the problems and side effects described below are associated. High-fidelity optics make it possible to shoot video of higher quality, but its disadvantages are additional weight due to the large amount of glass and a much higher price.

In addition, the quality of shooting affects the one-matrix or three-matrix photomatrix installed in video and 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 through the prism than it is processed by a filter in a single-matrix camera.

There are two main types of photomatrix - on charge-coupled devices (CCDs) and made on the basis of CMOS technology (complementary metal oxide semiconductor). The first one usually has a sensor, which receives light, and a processor that processes the image. In CMOS matrices, the sensor and the processor are usually combined. Under conditions of insufficient illumination, CCD cameras are usually given a better image quality, and the advantages of CMOS matrices are that they are cheaper and consume less energy.

The size of the photomatrix also affects the image quality. If shooting occurs with a small amount of light, then the larger the matrix - the better the image quality, and the smaller the matrix - the more problems with the image - it produces digital noise. Large matrices are installed in more expensive cameras, and for them a more powerful (and, as a consequence, heavy) optics is needed. Cameras with such a matrix allow you to shoot professional video. For example, recently a number of films were filmed completely on such cameras as Canon 5D Mark II or Mark III, in which the size of the matrix is ​​24 x 36 mm.

Manufacturers usually indicate in what minimum conditions the camera can operate, for example, with an illumination of 2 lux. This information is not standardized, that is, the producer decides for himself which video is considered qualitative. Sometimes two cameras with the same minimum illumination give different shooting quality. Alliance of Electronic Industries EIA   (from the English Electronic Industries Association) in the USA proposed a standardized system for determining camera photosensitivity, but so far it is used only by some manufacturers and not universally accepted. Therefore, to compare two cameras with the same light characteristics, you need to try them in action.

At the moment, any camera, even designed to work in low light, can give a picture of poor quality, with high graininess and afterglow. In order to solve some of these problems, it is possible to take the following steps:

• To shoot on a tripod;
• Work in manual mode;
• Do not use the variable focal length mode, but instead move the camera as close as possible to the subject;
• Do not use automatic focus and automatic ISO selection - at higher ISO values, noise increases;
• Shoot with 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 lights and moonlight.

Despite the lack of standardization of the sensitivity of the cameras to the illumination, it is still better to choose a camera for night shooting, on which it is indicated that it works at 2 lux or lower. It should also be remembered that even if the camera is really good at shooting in dark conditions, its sensitivity to illumination in the suites is sensitivity to light directed at the subject, but the camera actually receives light reflected from the subject. During reflection, some of the light is scattered, and the further the camera from the object - the less light enters the lens, which degrades the quality of the survey.

Exposure number

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

Several combinations of shutter speed and aperture in the camera at the same exposure number make it possible to obtain approximately the same image density. However, the images will be different. This is due to the fact that for different values ​​of the diaphragm the depth of the sharply depicted space will be different; at different shutter speeds, the image on the film or matrix will be at different times, as a result of which it will be blurred or not blurred at all. For example, combinations 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 smeared, and the second will have a shallow depth of field and, quite possibly , will not be blurry at all.

Higher EV values ​​are used if the subject is better illuminated. For example, the exposure number (with ISO 100 sensitivity) EV100 = 13 can be used for landscape photography if there is cloudiness in the sky, and EV100 = -4 is suitable for shooting a bright aurora.

A-priory,

EV = log 2 ( N 2 /t)

2 EV = N 2 /t, (1)

  Where
• N   - a diaphragm 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 the combination f / 2 and 1/30, the exposure number

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

This number can be used for shooting night scenes and lighted showcases. The combination f / 5.6 with exposure 1/250 gives the exposure number

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 shoot a landscape with a cloudy sky and without 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.

Interrelation of the exposure number with brightness and illumination of the subject

Determination of the exposure to the brightness of light reflected from the subject

When using exposure meters or luxmeters measuring the light reflected from the subject, the shutter speed and aperture are related to the brightness of the subject by the following ratio:

N 2 /t = LS/K (2)

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

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

EV = log 2 ( LS/K)

2 EV = LS/K

When 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 speed with which they dilapidate, fade and otherwise damage museum artifacts, depends on their illumination and on the strength of the light sources. Employees of museums measure the illumination of exhibits to make sure that the exhibits receive a safe amount of light, and also to provide enough light for visitors so that they can view the exhibit well. Illumination can be measured with a photometer, but in many cases it is not easy, because it should be as close as possible to the exhibit, and for this it is often necessary to remove the protective glass and turn off the alarm, and also get permission to do so. To facilitate the task, museum staff often use cameras as photometers. Of course, this is not a substitute for accurate measurements in a situation where a problem is found with the amount of light that gets to the exhibit. But in order to check whether a more serious check with a photometer is needed, the camera is enough.

Exposure is determined by the camera on the basis of indications of illumination, and knowing the exposure, you can find the illumination, having done a number of simple calculations. In this case, museum employees use either a formula or a table with the exposure transferred to the units of illumination. During the calculations, do not forget that the camera absorbs a part of the light, and take this into account in the final result.

Illumination in other areas of activity

Gardeners and plant growers know that plants need light for photosynthesis, and they know how much light is needed for each plant. They measure the illumination in greenhouses, orchards and orchards to make sure that each plant receives enough light. Some use photometers for this.