On Vision and Colors from a prism, however, the production of white can be demonstrated by using a mixture of colored light from each of the three main pairs of complementary colors: red – green, orange – blue, or yellow – violet. White can be produced from two complementary opposite colors when both of the external causes of the colors excite the same retinal place at the same time. Newton claimed that white could be produced by the aggregation of his seven prismatic colors. He erroneously considered color to be in light instead of in the eye. White is the result of the combination
Full-spectrum light phenomenon called metamerism. Where light sources use an electric discharge through low pressure gas, the light spectrum may be quite discontinuous, with some wavelengths of light missing or at very low amplitude. Such light sources have a strong tint, such as low pressure sodium lamps, or neon lamps. These lamps are used more for their color effects than for general illumination. Some scientific instruments use discharge tubes to produce light that has only a few wavelengths in it,a so-called "line spectrum". A laser is a single-wavelength source, which would produce light of a very pure color. Ideally, during the day,