Light temperature: definition, features and levels

The term "temperature of light" is, of course, not meant to mean the real temperature, but the color of light, or otherwise - the color gamut of light, the predominance of red or blue spectra.

Why is it important to know?

It is important to know about the color temperature of those who work directly with the light, for example, designers and photographers. Like no other, they can confirm that the right color gamut of light can either completely transform everything (be it a person in a frame or an interior) and spoil it.

Absolutely black body

The temperature of the light source is measured in degrees Kelvin. It is calculated by Planck's formula: the temperature at which an absolutely black body will emit light of the same color tone, this will be the desired value.

Thus, the determination of the color temperature occurs by comparing the desired light source with an absolutely black body. The regularity is interesting: the higher the temperature of the latter, the greater the blue spectrum prevails in light.

It is easiest to follow in practice: the color temperature of the incandescent lamp with warm white light is 2700 K, and the fluorescent fluorescent lamp is 6000 K.
Why so? Absolutely black body can be compared with iron, which is heated in the forge furnace. We all remember that the metal, red-hot, but still having a fairly low temperature, has a red light, and we often see the expression "incandescent" in the literature - that is, to a much higher temperature. So the black body emits light in this order of colors from red, orange and white, and ends with white and blue. That is, the lower the temperature of light, the warmer it is.

Some values

The visible spectrum of the red-hot body, the same "red-hot" metal, starts from 800 degrees Kelvin. This is a dim, dark red glow. The yellow light of the flame has a temperature already twice as high, from 1500 to 2000 K. Lamps, which are usually used for filming, give indicators of about 3250 degrees. The sun, which slopes towards the horizon, shines with a temperature of 3400 K, and the daylight temperature is almost 5000 K. The color temperature of the light of the flash is 5500-5600 degrees. Lamps with a multilayer phosphor, depending on the bin light, have values from 2700 to 7700 K.

Interesting paradoxes

Thus, the word "temperature" here acts as a determinant of color. At first it will be difficult to get used to the fact that the temperature of a clear blue sky (12 000 K) is ten times (!) Higher than the temperature of the flames of the fire (1,200 K). And in the area of the poles the sky is still "warmer" - about 20 000 K! The temperature of sunlight fluctuates during the day from 3000 to 7000 K.

Attention is also drawn to the fact that different shades have different light intensity, that is, they spread differently. Incorrectly will lead to the example of a candle flame, illuminating only a small fraction of space around itself, and a white LED, much brighter, but you can compare two identical LEDs of yellow and white colors. Despite the identical size and power, the yellow LED is dimmer, and the red light illuminates even worse.

Gradations

Often we meet with shades of the same color. In lighting, this is most often gradation of white: cold, neutral and warm. In fact, even such minor changes in the nature of the scale affect a tool as thin and precise as the human eye. These shades of white not only differently convey the color of the illuminated objects, but also behave differently in different weather conditions, as well as the distance range of their light beam.

All of the above features are taken into account by modern manufacturers when creating certain lighting devices, but to understand the difference with colors, you need to enter another important parameter.

Color rendition

The temperature of the light of the lamps is not the only thing that one should know. Another one of the basic terms in lighting equipment is color rendition. Surely everyone has to make sure that, depending on the lighting, we can perceive different colors in the same way. Yes, the names of flowers - just an agreement between people to designate a certain word by this or that wavelength perceived by us. In fact, our eye distinguishes about ten million different shades, but most of them we see in daylight, sunlight. He was taken for the standard.

Thus, the color rendition, or the degree of the overall color rendition, is the match of the light source to the standard or the ability to transmit the color of the illuminated object in the same way as in sunlight. It is measured in Ra, also the term color rendering index - CRI, the color rendering index is also used.

The standard has a value of 100 Ra (or CRI), and the lower this indicator is for a lamp or a flashlight, the worse this light transmits the natural shade of the object.

Best options

Temperature, light, humidity - the most important indicators of comfort in any room, so it is important to choose the right shade for lighting. The temperature of lamps and LED lamps with cool white light varies from 5000 to 7000 K. Cool white, as it is called by the manufacturers' labels, has a rather low color rendering index, only about 60-65, that is, in such a light the human eye perceives colors differently : Perhaps, everyone noticed how much everything changes in the "lifeless" pale blue light. However, it has the greatest contrast among all shades, and therefore is indispensable when it is required to illuminate objects that have a dark color (for example, wet asphalt, earth). Another feature of it is the efficiency at a long distance, so usually the "cool white" shade is used in long-range lanterns (the flow range is about 200 m).

Neutral white LED - neutral white - has a temperature in the range from 3700 to 5000 K. Its CRI is about 75, which means that the color rendition is an order of magnitude higher in comparison with cold bin. However, the distance of the light beam is lower, therefore, and the lights with neutral white light have a much shorter distance, but it is more comfortable for the eyes.

The temperature of warm light (warm white) is from 2500 to 3700 K. The color perception index is even higher, about 80, but the range is even smaller than that of the neutral bin. However, warm and neutral shades have an advantage over cold white if lighting is necessary under conditions of high smoke, humidity (rain, fog), and underwater if there is a slurry (for example, in ponds). In such situations, cool white is much more illuminated not by the object itself, but by the space before it, forming a tube of light.

For diodes

If for incandescent or fluorescent lamps you can stop only on the value of the color temperature, then for LEDs only it is not enough, so the so-called division into beans has appeared. In diodes, the predominance of blue (green) or pink shades is possible, so if you need several light sources, you must choose the same characteristics. The division into beans is different for some manufacturers, this should be taken into account, if, for example, in the office, it is required to replace the lamps.

In the work

As a rule, warm shades of light are good for creating a warm, cozy atmosphere. It is used in lighting restaurants, cafes, boutiques, in hotel lobbies, as well as in living quarters.

White light is more accustomed to the eye, suitable if you want to create a friendly, individual, but at the same time a working, non-relaxing atmosphere. In this light it is good to read, therefore such lamps are installed in libraries, as well as in shops and office premises.

Neutral white gives the effect of a friendly, safe and comfortable atmosphere. In addition to office space, it is used in exhibition halls and bookstores.

Cold light creates a clear, clean and productive environment. It is advised him for classrooms, supermarkets, hospitals, office space.

Lamps of daylight with a temperature of up to 5000 K underline the colors of objects, the atmosphere in this light appears bright and slightly disturbing. Such lighting will be appropriate in the hospital viewing room, in the gallery, the museum and the jewelry store, because in these spheres it is very important that the human eye perceives objects in their natural light.

Photo and video

Especially important is the knowledge of the temperature of light for photographers and cameramen, as well as for people involved in correcting photos and video. Since in cold lighting the camera removes everything in unnatural light, this must be taken into account in further processing.

At the time of the film, everything was much more complicated. Negative and slide variants were produced only for filming under daylight (about 5700 K) or for warm yellow light (2500-2700 K, the so-called evening film). Only in this way was it possible to obtain an adequate display of colors, without the use of additional correction or filters.

Masked negative color films were produced already at an average temperature of 4500 K.

In the digital age

In our time, almost no one is filming. Modern digital cameras have in the settings color correction, it can be both automatic and manual. This function is called "white balance". It is best to perform correction directly when shooting. You can correct it in the finished file, but this often leads to loss of quality, incorrect display of colors, and sometimes noise may appear in the picture. You can edit the color gamut without losing quality if the file is recorded in digital RAW format (Nikon cameras - NEF).