On Vision and Colors tried to demonstrate physiologically that color is "specially modified activity of the retina." The initial basis for Schopenhauer's color theory comes from Goethe's chapter on physiological colors, which discusses three principal pairs of contrasting colors: red/green, orange/blue, and yellow/violet. This is in contrast to the customary emphasis on Newton's seven colors of the Newtonian spectrum. In accordance with Aristotle, Schopenhauer considered that colors arise by the mixture of shadowy, cloudy darkness with light. With white and black at each extreme of the scale, colors are arranged in a series according to the mathematical ratio between the proportions of light and
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,