Purkinje effect

Lore & Background

The effect was first described in 1825 by Jan Evangelista Purkyně, a Czech anatomist and polymath. Purkyně often meditated at dawn during long walks in blossomed Bohemian fields, where he noticed that his favorite flowers appeared bright red on a sunny afternoon but looked very dark at dawn. He reasoned that the eye has two systems adapted to see colors: one for bright overall light intensity and another for dusk and dawn.

Reader's Guide

The Purkinje effect occurs at the transition between photopic (cone-based) and scotopic (rod-based) vision, in the mesopic state. As intensity dims, rods take over, and before color disappears completely, sensitivity shifts toward the rods' peak sensitivity at about 507 nm (greenish blue). This effect introduces a difference in color contrast under different levels of illumination; for example, in bright sunlight geranium flowers appear bright red against dull green leaves, but at dusk the red petals appear dark red or black while leaves and blue petals appear relatively bright. The insensitivity of rods to long-wavelength red light has led to practical uses: red lights are employed in submarine control rooms, aircraft cockpits, research laboratories, and naked-eye astronomy to allow dark adaptation while permitting reading. The effect also affects visual estimates of variable stars in astronomy when comparison stars of different colors are used.

Did You Know?

• The Purkinje effect is named after Czech anatomist Jan Evangelista Purkyně, who first described it in 1825.
• At low illumination, reds appear darker relative to other colors because the eye's peak sensitivity shifts toward blue.
• Rods are insensitive to long-wavelength red light, which is why red lights are used in submarines and aircraft to preserve night vision.
• The effect can affect visual estimates of variable stars when comparison stars of different colors are used.