Some animals, including many birds, see ultraviolet light that human eyes cannot detect.

The longer version

Many birds, insects, and some reptiles carry a fourth cone type tuned to wavelengths below what human eyes register. Their lenses also pass ultraviolet instead of filtering it out, as ours do, so short-wave light actually reaches the retina. Bees, for instance, work with ultraviolet, blue, and green and have no red receptor at all.

The ability pays off in ways invisible to us: urine trails left by small mammals glow under ultraviolet, ripe berries carry ultraviolet sheens, and plumage patterns that look plain to people can be striking to a bird. Reindeer are thought to use ultraviolet contrast to spot lichen and predators against snow.

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

Mixing red, green, and blue light in equal amounts produces white light on a screen.

Mixing yellow and blue paint produces green, which surprises people taught that mixing light works differently.

Pigments create color by subtracting wavelengths, while lights create color by adding wavelengths together.

A shadow's edges grow blurrier as the light source becomes larger or moves farther away.

The darkest part of a shadow is called the umbra, while the softer edge is the penumbra.

A periscope uses two mirrors to let a viewer see over an obstacle.

A mirror swaps left and right in reflections, though it really reverses front and back.

Kaleidoscopes create symmetrical patterns by reflecting light between angled mirrors inside a tube.

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