What goes black

Science in dialogue

How is the color black created?

Black is actually not a color at all. Because the colors such as red, green or blue that we see correspond to light waves with a certain wavelength or a certain frequency. These waves are radiated, reflected or, for example, transmitted by glasses, from all objects. So it depends on whether the light of a certain wavelength reaches the eye or not.

Usually (the laser is an exception) light waves of different wavelengths are superimposed, whereby the individual colors add up. This is used, for example, in televisions and computer monitors to add as many combinations as possible from 3 basic colors. Depending on the selection of the basic colors, it is difficult or impossible to achieve certain colors such as a bright yellow or a rich green.

By cleverly combining the 3 basic colors on the screen, it is possible to create the impression that we call the color "white". In nature, white is usually composed of (almost infinitely) many light waves of different wavelengths. Black, on the other hand, means the absence of all corresponding light waves. This can be due to the fact that a material neither transmits nor reflects light, nor does it emit any significant amount of light. Therefore, black is actually not a color, but the absence of color.

In fact, a so-called black body always emits electromagnetic waves of various wavelengths; visible light is only a special selection from this spectrum. How strong this radiation is at different wavelengths is very closely related to the temperature of the body. When heated, the maximum radiation is first shifted into the infrared range of thermal radiation, then into the range of visible red light and finally to shorter wavelengths, which can be seen very nicely when metals are annealed. This effect is used, among other things, to determine the temperature of stars.

The question was answered by Prof. Dr. Michael Schreiber, Professor of Theoretical Physics at the TU Chemnitz.