VISIBLE white light is a mixture of all wave lengths of light visible to the eye. The human eye perceives wave lengths of 400 to 700 mμ (4,000 to 7,000 Angstrom). Each wave length is associated with a spectral color and all colors of the spectrum can be produced by mixtures of three hyopthetical primary colors of light: red, green, and blue. The primary colors of light are different from the primary pigment colors. Individuals with normal color vision are referred to as trichromats, indicating that three primary colors are required in fixed relationship to match any spectral color. Subjects with defective color vision can be classified as follows. (1) Anomalous trichromats are nearly normal but require abnormal amounts of three primary colors when matching all areas of the spectrum. Approximately 75% of color deficiency in males is of this type, which is X-linked recessive in inheritance. (2) Dichromats are