Newton’s Green and Goethe’s Purple – Color Experiments with LEDs

White light refracted by a glass edge or a prism might be split into the colors of the rainbow but, when restricted by a suitable arrangement of edges, might also yield a sequence of colors complementary to the rainbow. We studied the creation of these color fields experimentally with a setup consisting of RGB light-emitting diodes that cover all color combinations of the three primary colors red, green, and blue. These light fields were projected through a prism onto a screen or a camera to generate various color fields by refraction. Applying the rules of additive color mixing, a simple RGB model based on the slit spectrum of the light convincingly reproduces the observed color patterns. The parallel use of model and experiment enables a clear recognition of unusual spectra from particularly combined light fields and yields an explanation of their origin.