The Purkinje Effect — Why Colours Shift at Night

The Purkinje effect is one of those phenomena that, once you know it exists, you will see everywhere. It describes the shift in the eye's colour sensitivity as lighting conditions transition from photopic — cone-dominated, bright — to scotopic — rod-dominated, dim.

In bright conditions, your eye is most sensitive to wavelengths around 555 nanometres: yellow-green. In dim conditions, peak sensitivity shifts to around 507 nanometres: blue-green. Reds, which sit at the long wavelength end of the spectrum, appear to darken and recede relative to everything else. Blues and blue-greens appear relatively brighter, even at low absolute luminance levels.

The consequence for lighting design is subtle but significant.

A warm, red-heavy colour palette — terracotta walls, deep burgundy upholstery, rich timber — that reads as luxurious and enveloping under well-lit conditions may feel flat, heavy, or slightly grey at night under low-level warm lighting. The reds that gave the space its richness in daylight have receded. The warmth that felt intentional now feels dim.

Conversely, a cool accent — a blue-grey stone, a steel-coloured fabric, a green plant — that sits quietly in a warm daytime scheme can appear disproportionately vivid at low evening light levels, drawing attention in a way that was not intended.

For designers specifying schemes intended to perform across the full day — residential spaces, restaurants, hotel rooms — the Purkinje effect argues for evaluating the palette and the lighting together at the light levels intended for evening use, not only in the conditions present during a daytime site visit. What you see at noon under ambient daylight is not what the occupant experiences at 10pm under controlled artificial light.

The eye you design for at noon is not the eye occupying the space at midnight.