two colors that form a color that is seen by the eye as white when the radiations of which they are composed are mixed (combined). The radiations composing the complementary colors may have components that are very different, ranging from the monochromatic to radiations with a continuous spectrum.

To obtain two beams of light with a continuous spectrum that meet the requirements of complementary colors, it is sufficient to pass a beam of white light (for instance, sunlight) through a nonabsorbent, color-selective mirror that strongly reflects one part of the spectrum (for example, the blue) and transmits the other part of the spectrum which will have a color complementary to the first color. (For example, blue will be complemented by yellow.)