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

The longer version

Screens place tiny red, green, and blue elements side by side and vary their brightness independently. At a viewing distance the eye cannot resolve the individual elements, so the three cone signals blend, and equal output from all three produces the same response as broadband white light, even though no white wavelengths are present.

The trick works because perception depends on the ratio of cone stimulation, not on the physical mixture of wavelengths. Two very different spectra can therefore look identical, a quirk called metamerism. Theater lighting and stage washes rely on the same additive rule when overlapping colored beams produce white.

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.