Red light bends least through glass, while violet light bends the most.

The longer version

The refractive index of glass is not a single number but a curve that rises toward shorter wavelengths. Violet therefore slows more than red inside the material, so a slanted entry separates the two, with violet deflected through the larger angle. Red stays closest to the original path.

This wavelength dependence is called dispersion, and it is what lets a prism spread light into a band. It also causes chromatic aberration, the colored fringing seen around high-contrast edges in simple lenses. Telescope makers combine glasses of different dispersion to cancel the effect, an arrangement known as an achromatic doublet.

Where this entry sits

These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.

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More From Color and Light

Eight more entries

The color orange takes its name from the fruit, which had the word first.

Purple and violet describe similar hues, though violet refers to a single wavelength of light.

Many languages have fewer basic color words than English, sometimes grouping blue and green together.

Turquoise sits between blue and green on the spectrum and is named after a gemstone.

Gold and silver describe metallic surface appearances rather than one particular wavelength of light.

The color of a flame changes with temperature, shifting from red toward blue as it gets hotter.

Optical illusions trick the brain by exploiting the shortcuts it uses to interpret light and edges.

Afterimages appear when staring at a bright color fatigues the cone cells responding to that hue.

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