What is the phenomenon where light separates into its component colors?

The phenomenon where light separates into its component colors is called dispersion. It occurs because a material’s refractive index depends on light’s wavelength, so different colors change speed and bend by different amounts when they pass through it.

A glass prism demonstrates dispersion clearly. White light entering the prism contains many visible wavelengths. In ordinary transparent materials, shorter-wavelength blue and violet light usually experience a higher refractive index than longer-wavelength red light, so they are deflected more strongly. The colors therefore emerge at different angles and form a spectrum.

Dispersion helps create rainbows, where raindrops act like tiny prisms, although reflection inside each drop is also part of the process. It can also cause chromatic aberration in cameras, telescopes, and microscopes because different colors do not focus at exactly the same point. Dispersion is not the same as diffraction, which spreads waves around edges or through openings, or reflection, which sends light back from a surface. Refraction is the bending itself; wavelength-dependent refraction produces dispersion.