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Why do different colors of light bend by different amounts in a glass prism?

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Isaac Newton Isaac Newton, oil on canvas by Sir Godfrey Kneller, 1702; in the National Portrait Gallery, London. Newton's discoveries in physics and mathematics revolutionized science.

Different colors of light bend by different amounts when passing through a glass prism because of a phenomenon known as chromatic dispersion.1

This occurs because the speed of light within a transparent medium like glass is not constant for all colors; rather, it depends on the light's wavelength. As light enters the prism, its speed decreases, and the degree of this change varies by color. Because the refractive index of the glass is inversely proportional to the speed of light within it, the index of refraction also varies by wavelength.123

Consequently, each color is refracted—or bent—at a slightly different angle. For example, violet light, which has a shorter wavelength, experiences a higher refractive index and bends more than red light, which has a longer wavelength. Isaac Newton famously used this principle to demonstrate that white light is not simple or homogeneous, but is instead a heterogeneous mixture that can be analyzed into its constituent colors through refraction.241