Hot & Cold

Hot & Cold

With growing popularity of LED lighting such feature as color temperature is becoming more common to buyers. You can find it marked on bulb’s body or packaging, indicated in Kelvin degrees. Let’s define what is the color temperature, and how can we use it in lighting design.

We got used to determine the color temperature by sensorial perception. Each of us will probably call the light of red or yellow tint as warm, and bluish one as cold. We also separate neutral tints which we usually match with natural daylight.

It’s also important to note, that color temperature refers not only to LED lamps. The light of any source has its own temperature. We’ve collected the most common light sources in our chart to help you find the closest analogue.



So what is the origin of color temperature? Let’s answer in terms of science.

Physics of Light

Color temperature


Almost any encyclopedia gives us the following definition by Max Planck:

Color temperature is the temperature of an ideal black-body radiator that emits light of comparable hue to that of the light source.

Probably, this definition won’t be clear to everyone. So let’s get down to the nuts and bolts.

The Nature of Color

Such phenomenon as color is only possible in the presence of 3 components:

  1. The observer
  2. The object
  3. The light source

Although we perceive white light as colorless, it contains all colors of visible spectrum from red to purple. When falling on an object, the part of the spectrum becomes absorbed by its surface, and another part reflects. Our eyes perceive only the reflected rays. So we see an object as red because it’s surface reflects only red light.

If the object absorbs all spectrum, it seems as black. So we can say that the black is really colorless.

In physics there is a concept of an ideal black-body – the body, that absorbs all incident radiation. Such objects don’t really exist. All that seems to be black is not ideally black – it always reflects some light.

The Origins of Light

The light correlates to temperature. The lowest possible temperature in our universe is called the absolute zero and equals to 0K or -273,15°С. At this temperature molecular motion stops and bodies cease to emit radiation (thermal, ultraviolet, visible, etc.) and become ideal black.

This temperature is also unobtainable. Every object in our universe is warmer, thus it produces, at least, heat emissions.

If you continue heating the object, it starts glowing visibly with dim red light at 800К (527°С). When the body becomes hotter, its light becomes bluish. So here we meet a kind of a paradox: the warmer is the body, the colder is its light.

Psychology of Light


Color temperature has not only physical but also psychophysical meaning. You must have noticed that our mood and perception often respond to changing light.

Natural Light

Such kind of lighting is the most common in offices. According to numerous researches, the light within 3500-4500 K ensures the highest work performance. Warmer light (3000 K) downgrades productivity by 5-7%. Further color temperature drop leads to “cradling” effect and 25% of productivity loss. Cold displacement also has negative consequences: first you can observe explosive performance growth, but than it quickly becomes replaced by 25% decay due to fatigue.

Cold Light

Cold hues can also become a useful solution for some facilities. For example, cold light is widely used for lighting up production lines. It helps maintenance staff to concentrate. The most “frosty” light is common for diagnostic rooms, laboratories and other places where high short-term concentration is important.

Cold light is also suitable for hospital wards, pharmacies, bathrooms and kitchens. It helps to create the atmosphere of cleanness and sterility.

Warm Light

Warm light is good for creating cozy domestic atmosphere. It is the most suitable for kindergartens, restaurants, theaters, libraries and living rooms – the places where you relax.

Lighting and Marketing


Psychologic effects caused by lighting have been a special matter of many marketing researches. As a result, various rules of how the products should be lit were created.

For instance, bread, cheese, fruits and vegetables look the best in warm light. Meat and milk prefer cold hues. The coldest light is in the freezers. The only exception here is fresh fish and seafood – they look more attractive in warm lighting.

Warm-lit furniture, carpets and bed-linen look cozier than in cold or neutral light. Such tints are the most suitable for electronics and hi-tech devices.

You can often meet cold lighting in floral shops. It makes flowers look fresh. The only plant that prefers neutral lighting is cactus.

The Most Comfortable Light

The right tint is not always enough for making comfortable lighting. Color temperature perception also depends on its brightness. This rule was developed by Dutch scientist Arie Andries Kruithof. He demonstrated people the light sources of different colors and luminosity and asked to rate how comfortable their light is.

As a result, the following chart was developed:

 comfortable lighting


The chart shows how the color perception is aligned with the light’s brightness. For example, the lamp with color temperature of 2700K will look pleasant in 200lx luminosity. But if we take a brighter lamp, it’s light will probably be annoying.


As we can see, the color temperature is quite an important feature. We hope this article will prove itself useful and help you select the most appropriate LED lamp.


Find the most useful advice on LED lamps selection in our short article How to Choose an LED bulb?

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