Optics is the science of light and how it interacts with the world. Optics explains how rainbows exist, how light reflects off mirrors, how light refracts through glass or water, and what splits light shining through a prism. In addition to visible light in the standard "spectrum" of red, orange, yellow, green, blue, indigo, and violet, optics also deals with invisible parts of the whole electromagnetic spectrum of which visible light is but a small part.