Correspondence between wavelength and color temperature. Color temperature of LED lamps and luminaires
In lighting technology, color temperature is the most important characteristic of light sources, determining the color of the lamps and the color tone (warm, neutral or cool) of the space illuminated by these sources. It is approximately equal to the temperature of a heated body of the same color as a given light source. Color temperature is measured in degrees Kelvin (K). In practical lighting engineering, it is useful to associate the color temperature reproduced by artificial light sources of various types with natural light sources.
The color temperature scale is divided into three ranges: warm white, neutral white (natural) and cool white.
The sun, a natural source of light, has a very high physical temperature, but the equivalent color temperature of the light we receive at the Earth's surface fluctuates depending on the time of day and weather conditions. This occurs as a result of the reflection and refraction of light in the atmosphere.
We provide you with a comparative table of natural and artificial light sources:
Warm white
1850 - 2000 K
Sources of artificial lighting that reproduce this color temperature are the flame of a stearin candle. The natural light source is the morning or evening twilight sky (2000 K).
2000 – 2700 K
Sources of artificial lighting that reproduce this color temperature are incandescent lamps up to 40 W, high-pressure sodium lamps (HPS). Natural light source - the sky near the rising or setting Sun (2300 - 2400 K)
2700 - 2800 K
Sources of artificial lighting that reproduce this color temperature are 60W incandescent lamps, mains voltage halogen lamps, fluorescent lamps (FL), compact fluorescent lamps (CFL), light emitting diodes (LED).
2800 - 3500 K
Sources of artificial lighting that reproduce this color temperature are incandescent lamps 75-500W, mains voltage halogen lamps, low-voltage halogen lamps, LL, CFL, LED.
3500 K
Sources of artificial lighting that reproduce this color temperature are mains voltage halogen lamps, low-voltage halogen lamps, LL, CFL, metal halide lamps (MHL), LED. Natural light source – Sun one hour after sunrise/before sunset
The sensitivity of the human eye to the perception of color temperature is non-linear. A 500K difference in the warm part of the color temperature range is more noticeable than the same difference in the cold part of the range, so light source manufacturers offer a larger range of lamp colors in the warm range.
Neutral white
 |
4000 K Sources of artificial lighting that reproduce this color temperature - LL, CFL, MGL, LED / LED. Natural light source – Moon (4125 K) |
Cold white 
5000 K
Sources of artificial lighting that reproduce this color temperature - LL, CFL, MGL, LED / LED. A natural source of light is the morning or evening Sun in a clear sky at an angle of more than 15 degrees above the horizon (3600 - 5000 K).
5500 K
Sources of artificial lighting that reproduce this color temperature - LL, CFL, MGL, LED / LED. The natural source of light is the Sun around noon with light clouds (5100 -5600 K).
6500 K
Sources of artificial lighting that reproduce this color temperature - LL, CFL, MGL, LED / LED. The natural source of light is the summer Sun at its zenith in a clear blue sky (6000 - 6500 K).
7000 K
Sources of artificial lighting that reproduce this color temperature - MGL, LED / LED. The natural source of light is daylight from the sky with high, light clouds (6700 -7000 K).
12000 K
The natural light source is daylight from the sky with light clouds (12,000 - 14,000 K). The color temperature of a clear blue sky is 15,000 – 27,000 K.
William Kelvin, a British physicist, discovered in the late 19th century that a cube of coal, when heated to different temperatures, glows in different colors, ranging from deep red throughout the visible spectrum.
The color temperature of the sky on a cloudy day ranges from 6000 to 7500°K. This doesn't mean the sky is that hot. Color temperature indicates to what temperature Kelvin would have to heat his black carbon cube to cause it to emit the appropriate hue of color. So it's just a convenient way to quantify color in a way that everyone can understand.
The Kelvin temperature scale, unlike the Celsius and Fahrenheit scales, starts at “absolute zero,” the theoretical temperature at which molecular motion should cease completely.
Color temperature of some light sources
Color temperature of electric lamps.
Color temperature scale for common light sources
- 800 K - the beginning of the visible dark red glow of hot bodies;
- 1500-2000 K - candle flame light;
- 2800 K - 100 W incandescent lamp (vacuum lamp);
- 2800-2854 K - gas-filled incandescent lamps with a tungsten filament;
- 3200-3250 K - typical film lamps;
- 3800 K - lamps used to illuminate meat products in a store (have a high content of red color in the spectrum);
- 4200 K - fluorescent lamp (warm white light);
- 4300-4500 K - morning sun and lunchtime sun;
- 4500-5000 K - xenon arc lamp, electric arc;
- 5000 K - sun at noon;
- 5500 K - clouds at noon;
- 5500-5600 K - photoflash;
- 5600-7000 K - fluorescent lamp;
- 6200 K - close to daylight;
- 6500 K is a standard daytime white light source, close to midday sunlight;
- 6500-7500 K - cloudy;
- 7500 K - daylight, with a large share of scattered light from a clear blue sky;
- 7500-8500 K - twilight;
- 9500 K - blue cloudless sky on the north side before sunrise;
- 10,000 K - an “infinite temperature” light source used in reef aquariums (anemone blue tint);
- 15000 K - clear blue sky in winter;
- 20000 K - blue sky in polar latitudes;
Fluorescent lamps
Typical color temperature ranges at maximum luminous efficiency of modern fluorescent lamps with multilayer phosphor:
- 2700-3200 K,
- 4000-4200 K,
- 6200-6500 K,
- 7400-7700 K.
Application
- characterizes the spectral composition of the light source radiation,
- is the basis for the objectivity of the impression of the color of reflective objects and light sources.
For these reasons, it determines the color of objects perceived by the eye when observed in a given light (psychology of color perception).
Light sources in printing
To obtain the most accurate color image at all stages of production, it is often recommended to maintain a standard color temperature of lighting of 6500 K (source D 65): from order acceptance through evaluation of originals, scanning, retouching, screen proofing, digital proofing, color separation, analog proofing, printing proofs , for circulation printing and final delivery of printed products.
The D 65 source with a color temperature of 6500 K has in its spectrum an ultraviolet component defined by the standard. Although the human eye does not perceive ultraviolet rays, many objects (including dyes) are capable of glowing under their influence. For example, without a UV component, paper will not be as white (optical brighteners are introduced into it), and advertising will not be as bright (they often use
June 27, 2018The color temperature of LED lamps is an important characteristic for reducing eye strain. The temperature property of the lamp's light determines how comfortable and familiar the lighting that this lamp provides will be to the eye.
When talking about color temperature, we are not talking about literal temperature, although expressions such as warm light or cool light are used. When they say warm LED lamps, they do not mean the heat transfer of these lamps. We are talking about the subjective perception of light by the human eye.
A simplified definition of the term color temperature is the conditional glow of a conditional “black” body that is heated to a particular temperature. For example, warm light is light whose characteristics coincide with the conventional radiation of a “black body”, which is heated to a temperature in the range from 800 Kelvin to about 3000 Kelvin.
When applied to lamps, the expression “warm light” or “warm lamp” usually means that the lamp produces light whose temperature is 2700 Kelvin. Light of this temperature is produced by an incandescent lamp with a power of approximately 80 watts. For incandescent lamps, color temperature increases as lamp wattage increases. For example, a 40 W incandescent lamp produces light with a temperature of 2200 Kelvin, and a 100 W incandescent lamp produces light with a temperature of 2800 Kelvin.
Subjectively, this is felt as the degree of “yellowness” of the light. A low-power lamp produces a very yellow light, and as the power increases, the light becomes “whiter” and the yellow-red tint in it decreases. In incandescent lamps, the color temperature depends on the power of the lamp; the more powerful the lamp, the more the tungsten filament heats up. And the more the spiral heats up, the “whiter” the light from it becomes. There is even an expression - white-hot.
In LED lamps, the color temperature is set using a phosphor that is applied to the surface of the LEDs. And LEDs themselves produce very “cold” light, with a shift to the blue part of the spectrum.
List of color temperatures for some light sources:
- 800 K - the beginning of the visible dark red glow of hot bodies;
- 1500-2000 K - candle flame light;
- 2000 K - high pressure sodium lamp;
- 2200 K - incandescent lamp 40 W;
- 2680 K - incandescent lamp 60 W;
- 2800 K - 100 W incandescent lamp (vacuum lamp);
- 2800-2854 K - gas-filled incandescent lamps with a tungsten filament;
- 3000 K - 200 W incandescent lamp, halogen lamp, warm white fluorescent lamp;
- 3200-3250 K - typical film lamps;
- 3400 K - the sun is at the horizon;
- 3500 K - white light fluorescent lamp;
- 4000 K - cold white fluorescent lamp;
- 4500-5000 K - xenon arc lamp, electric arc;
- 5500-5600 K - photo flash;
- 5600-7000 K - fluorescent fluorescent lamp;
- 6200 K - close to daylight;
- 6500K is a standard daytime white light source, close to midday sunlight.
Since in LED lamps the light temperature is set using a phosphor (as in fluorescent lamps), there are LED lamps with different light temperatures - 2700 K, 4000 K, 6500 K.
Warm LED lamps
The so-called warm LED lamps are LED lamps with a color temperature of 2700 K. Such lamps are best used in residential areas. The spectrum of their light is close to the light of incandescent lamps and therefore will be more familiar to the eyes. It is better to use warm LED light even if both incandescent and LED lamps are used in the room. In this case, it will be more comfortable for the eyes due to the absence of a sharp difference in light between lamps of different types. There will be no sharp transitions between “warm” and “cold” light.
But when choosing LED lamps, you need to keep in mind that for cheap lamps the actual color temperature may be higher, and significantly higher than the declared 2700 K.
LED lamps 4000 K and 6500 K
Personally, I do not recommend using lamps with a color temperature of 4000K or 6500K. The problem is that for LED lamps with a temperature of 4000K and even more so 6500K, the spectrum (temperature) of light does not correspond to the strength of this light. In nature, the temperature of light increases with the strength (intensity) of that light. For example, on a sunny summer day, in the middle of the day, sunlight has a temperature of more than 6000 Kelvin. At the same time, the light intensity is very high, it is bright, even blinding. And in the case of an LED lamp with a temperature of 6500K and a luminosity of 1000 lumens, the luminous flux that this lamp produces does not correspond to this temperature. In nature, the temperature of light, for such a luminous flux, will be approximately 2600 - 2700 K (for example, an incandescent lamp).
This discrepancy between temperature and light intensity creates discomfort. It is no coincidence that the expression “dead light” was coined for fluorescent lamps (in which cold phosphor was first used).
Lamps with high (cold) temperatures are suggested as more suitable for workplaces. Supposedly they provide better lighting. Actually this is not true. The quality of workplace lighting primarily depends on the intensity of the light. Therefore, two lamps, each 1000 Lumens, with a temperature of 2700K will give better illumination than one lamp of 1000 Lumens with a temperature of 4000K.
Over time they become more and more popular. The use of these modern lighting sources is used in various areas of the national economy and industrial production. used in cars, outdoor advertising, illuminate production workshops, residential buildings, and also illuminate city streets. In offices they are built into lamps. It is no longer possible to imagine powerful spotlights without such sources of light flux.
The color temperature of LED bulbs is often mistaken for the amount of heat emitted, but it has a slightly different meaning. This concept means the visual effect of the perception of a light source by the human eye. The amount of “warmth” of the lamp depends on the distance of the color spectrum from the solar luminous flux. The bluish tint is similar to an overcast sky or night glow. Such light causes cold sensations in a person.
Color temperature range
When the metal is heated, a specific glow appears. At the beginning the color interval has red shades. But as the temperature increases, the color spectrum gradually approaches yellow, white and then blue and violet.
Each color of metal glow has its own temperature range, which makes it possible to describe this phenomenon in physical quantities. This defines the properties of color temperature as a certain range of heating until the required color of the spectrum is formed.
LEDs emit light with a slightly different spectrum, different from metal light, since it has a different nature of origin. However, the essence remains the same: to create a certain shade of color you will need a given color temperature. In this case, it cannot be considered that this parameter is related to the heating temperature of the lamp; physical and color temperatures are completely different indicators.
Scale for light sources
Today, a large list of light sources based on LED crystals is offered for sale. They operate in different temperature ranges. Most often, they are selected according to the location of the planned installation, since each lamp is capable of creating an individual look. A room can be transformed by changing the color of the light output from the lamps.
To rationally use an LED lighting source, you need to determine in advance which color is most comfortable for you. Color temperature is important not only for LED lighting devices; it depends on the composition of the emission spectrum. Each lighting device has this indicator, for example, the light is only warm yellow.
With the advent of lamps, cold white light came into use. And LED lamps have a wider range of light colors, so the choice of such lamps has become more complex, and the shades of colors depend on the semiconductor material.
Relationship between lighting and color temperature
If you know the table values of this parameter, then the corresponding colors become clear. Each person has an individual perception of color, so visually determining color temperature is very difficult.
The basis is considered to be the average performance of a certain group of light sources operating in a certain spectrum, and in the final selection of LED light sources, their purpose, the illuminated room and installation location are taken into account.
Groups of LED lamps by color temperature
- Warm white light is in the color temperature range 2700-3200K. This lighting spectrum is similar to a simple incandescent lamp. Such lamps are recommended for use in residential premises.
- Day white light Lamps emit in the range of 3500-5000K. Their light is similar in appearance to morning sunlight. This is a neutral light that can be used, for example, in the toilet, hallway, school classrooms.
- Cool white light called daytime, which refers to the range of 5000-7000K. This creates an analogy to bright daylight. Such lamps are most often used in laboratories, medical institutions, parks and billboards.
From these parameters it can be seen that the low color temperature of LED lamps has a predominantly red color, and no blue color at all. As this parameter increases, blue and green colors appear, and red gradually disappears.
Where is the color temperature of LED lamps indicated?
Most often, the manufacturer indicates its parameters on the lamp packaging. Among other characteristics, there is this parameter we are considering. Before purchasing lamps you should pay attention to this. These data are indicated both on the packaging and on the lamp body.
For each room, you should individually select lamps that have a given color spectrum of light.
For office
It is advisable to use LED lighting devices with a color temperature of 4400-5600 K. This means that the lamp should shine with white light. This improves employee productivity.
When installing lamps in an office with a different color shade of light, the efficiency of employees will decrease. Studies have shown that orange-emitting lamps impair performance by up to 80%. White or neutral light contains blue spectrum, which speeds up concentration and reaction during the daytime.
For residential premises
For an apartment or house, it is recommended to install lighting devices that have a different color temperature of LED lamps, different from office models. Blue spectrum lamps are not recommended for use in a bedroom or nursery.
The color temperature of LED lamps for the living room can be selected in the range from 2700 to 3200 K, which creates a comfortable and cozy environment.
Before understanding what color temperature is, it makes sense to first remember what temperature is in general, why bodies are hot and cold.
Temperature is the movement of the atoms that make up all bodies. The more mobile the atoms are, the more they vibrate, the higher the body temperature will be. Celsius came up with a temperature scale using water as a reference point. At zero degrees it should turn into ice, and at one hundred it should boil (at a specified atmospheric pressure). Kelvin found out that there is a limit of cold - a state when all the atoms of a body are motionless, and called such a temperature “absolute zero”, because the temperature in the Universe cannot be lower (in fact, it is impossible to slow down the already motionless atoms).
Kelvin used the Celsius scale, at which absolute zero was –273C. The Kelvin scale differs from the Celsius scale by precisely these 273 degrees, that is, the freezing point of water in Kelvin is 273K, and the boiling point is 373K. It's simple. We need this scale only because color temperature is measured in Kelvin.
Let's imagine a body, like soot, that does not reflect light at all, and let's call it an “absolutely black body.” To simplify the experiment, let us take as such a body a tungsten spiral in an electric light bulb. And let's start the experiment. First, let's lock ourselves in a dark room and turn off the lights. After your eyes get used to the darkness, we will begin to supply current to the light bulb through the power supply, gradually increasing the voltage.
Sooner or later the spiral will begin to glow with a barely noticeable crimson color. This means that it warmed up to about 900 degrees Celsius. This means that a completely black body begins to glow at 1200K. This will be the red end of the visible light spectrum. In other words, red has a color temperature of 1200K. Let's continue to increase the voltage. At 2000K the spiral will turn orange, at 3000K - yellow, at 5500K - white, at 6000K - blue, and then - violet. 18000K is the upper, violet limit of the spectrum of visible light (Of course, this is a speculative experiment, because in reality the spiral will burn out much earlier, tungsten will melt already at 3500K).
So, the color temperature of yellow is approximately 3000K. This means that in order to get exactly the same yellow color by heating the coil, it must be heated to just 3000 degrees Kelvin. Which, of course, will in no way mean that a blue object will be hotter than a yellow one. It is purely psychologically difficult for a person to get used to the fact that the color temperature of a candle flame (1200K) is lower than the color temperature of the clear sky (12000K). This leads to the conclusion: the color temperature of the light source can be changed. For this, the most ordinary light filter, painted glass, will do. The color temperature of an incandescent lamp can easily be increased to the same 12000K by inserting a filter into the spotlight. At the same time, the real thermal temperature of the filament was 2700K and will remain so.
Lamps and headlights
At first, cars were equipped with acetylene lamps, but they were quickly replaced by incandescent lamps. Over time, they improved, the diffuser and spotlight became better, but the light source invariably served as a tungsten filament. A regular incandescent lamp has a silicate glass bulb. The air is pumped out of it, and a tungsten spiral is attached to the electrodes. Such lamps have a lot of disadvantages: tungsten gradually evaporates, settles on the walls of the bulb, and the glass loses its transparency. The spiral becomes thinner, its resistance increases, and it eventually burns out. Tungsten cannot be heated indefinitely - the filament will melt. This means the glow will be yellowish. To increase the light intensity and brightness, you have to lengthen and thicken the thread, and the longer it is, the more difficult it is for the headlight to focus. Finally, the efficiency of an incandescent lamp is only 3% - the lion's share of electricity is uselessly converted into heat.
In the second half of the twentieth century, a new generation of incandescent lamps appeared: halogen. In such a lamp, the bulb is filled with gases from the halogen group. Its peculiarity is that the halogen returns particles of evaporated tungsten from the flask to the spiral. This means that it can be heated to a higher temperature, actually up to 2700–3000°C. The light output of halogen lamps reaches 22–25 lm/W - twice as much as that of classic lamps. A simple example: the luminous flux of an ordinary 45-watt car lamp is 600 lumens, and a 55-watt halogen lamp is more than one and a half thousand! Halogen glass does not become dirty over time, and its service life is significantly longer. The bulb made of heat-resistant quartz glass and the increased requirements for the accuracy of the spiral assembly affected the price: a “halogen” lamp is several times more expensive than a regular lamp.
And in the early 90s, gas-discharge lamps appeared on cars, which are commonly called “xenon” or simply “xenon”. There is no hot filament in such a lamp. Light is produced by a tiny sphere of gases (one of them is xenon, hence the name). The gases are heated by an electric arc to almost solar temperature, more than 4000°K. A 35-watt discharge lamp produces 3,000 lumens of light! There are lamps on sale with different color temperatures, from 3500K to 8000K.
3500K yellow - only suitable for fog lights
4300K white-yellow, such lamps come standard with the car
5000K white
6000K cool white with slight blue
7000K blue, lamp brightness is much lower, driving with blue light is bad
8000K blue – light purple, brightness is even worse
Of course, such a range in color temperatures is achieved not by different heating of the gas, but simply by tinting - additives are introduced into the gas mixture, which color the light flux. Interestingly, the best, most pleasing light to the eye is produced by lamps without dyes.
The light of a xenon lamp is easy to form into a precise light beam, which means it will be clearer. Such lamps are durable and not afraid of vibrations. Driving with xenon is a pleasure, visibility is simply amazing. It even gives the impression that high beams are not needed.
