Dispersion Chromatic dispersion occurs when the refractive index in a material is different for different wavelengths of light. The reason this happens is that no known medium except a complete vacuum is transparent to all electromagnetic waves. Glass, like most visibly clear materials, does not let much ultraviolet light pass through it. Close to wavelengths for which a medium is less transmissive, the refractive index rises substantially. What this means is that the purple end of the visible spectrum undergoes greater refraction in clear media than the red end does, and this separates the colors of while light into the usual striking spectrum. The figure to the right depicts white light, which is a mixture of the entire visible spectrum, being dispersed during refraction through a wedge-shaped piece of transmissive material called a prism . Of the three primary colors in white light, the path of red is typically bent the least, then green, and then blue is refracted the most.
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