For most people light is something that comes from the sun and makes the difference between day and night.



We can also create light artificially so that our life, at least in most cases, does not depend on sunlight. Colors are also an important part of out life, we take them for granted and we rarely think about the physical nature of colors. The fact is that light and colors are connected. Without light there are no colors. Colors are just different types of light. Another fact is that we heavily depend on our eyes - darkness is our enemy. We are lost, all other senses can not replace the vision.



What we call visible light is only a small part of the electromagnetic spectrum. Electromagnetic spectrum is usually related to frequencies which are further associated with radio, television and mobile communications. The only difference is that well known radio and television stations operate on frequencies in MHz range, while light frequencies are million times higher. Radio waves are also associated wavelengths. Wavelength is inversely proportional to frequency therefore light wavelengths are million times shorter than common radio and television wavelengths which are in the range of meters. So the light is some kind of radio communication. All the rules for radio wave propagation apply also to the light. We only need to take into account very high frequencies (or very short wavelengths - in range of nano meters).

What we sense as colors are only different wavelengths of electromagnetic radiation in the range of visible light. In other words, colors like red, orange, yellow, green, blue, violet and all hues between them are radio waves with wavelengths from 700 nm (red) to 400 nm (violet). The best and the most beautiful manifestation of this fact is the rainbow. What we see as sunlight is in fact a mixture of all wavelengths in visible spectrum. We call it white light. When there is no light we say it is black. From this point of view white and black are not colors. When white light passes through raindrops it is refracted. The angle of refraction depends on the wavelength. Therefore we can see all the colors or wavelengths that are present in normal white light. The rainbow is also a great example of "technical" colors - colors that represent individual wavelengths in visible spectrum.

Artificial lighting usually creates light which is not white - it is slightly colored but this does not cause any problems except in special cases where we need accurate color reproduction. In such cases we should use full-spectrum bulbs.