Laser light differs from ordinary light because its waves are aligned and share a single wavelength.

The longer version

Ordinary light is a jumble of wavelengths emitted in random directions with no fixed phase relationship between waves. Inside a laser, atoms are stimulated to release photons that match an existing wave exactly, so the beam ends up narrow, single-coloured, and coherent, with crests and troughs marching in step.

Coherence lets the beam stay tight over long distances and lets it interfere with itself, producing the speckled pattern laser light makes on a wall. Early devices used ruby crystals; gas tubes, semiconductors, and dyes followed. Because the energy is concentrated in one wavelength, even a weak beam can be dangerous to the retina.

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 traditional spectrum is often listed as seven colors, including red, orange, yellow, green, blue, indigo, and violet.

Most people cannot distinguish indigo from blue or violet in an ordinary rainbow.

Color blindness most often involves difficulty telling red from green rather than seeing no color at all.

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

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.

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