Colour Science & Perception
what the eye settles, and what it cannot
Concept

Brightness — where it appears

An appearance model's correlate for how much light a stimulus seems to emit, which needs no reference and is not luminance. Lightness is its relative counterpart and needs a white in the field; brightness does not, which is why a light in the dark has one and not the other.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

Brightness against chroma, at exactly constant luminance. Seven stimuli of identical luminance and rising chroma at hue 25. The model's brightness moves by 2.2 per cent across the whole sweep, and at some hues it moves the other way. The Helmholtz–Kohlrausch effect — measured repeatedly, by several methods — is that a saturated colour looks as bright as a neutral of 1.3 to 2 times its luminance, shown as the band. The gap is the model's, and nothing here closes it: the term that would is not in CIECAM16 and is not invented for the occasion.

Brightness is not luminance

Photometry is additive because the CIE defined it that way. Brightness is not, and a saturated colour looks as bright as a neutral of one and a half times its luminance — an effect this site's appearance model moves by two per cent, in a direction that depends on the hue.

brain · Appearance One light, seven rooms. The same stimulus — fixed in XYZ, unchanged throughout — shown against whites from 12 to 800 candelas per square metre. Its lightness falls from 152 to 16 and its brightness rises, because one of those is a ratio to the white and the other is not. Brown is the low-lightness end: a colour that exists only when something brighter is present, which is why no lamp is brown and no star is.

There is no brown light

Brown is dark orange, dark is a ratio to a white, and a light in a dark room has no white to be dark against. The same stimulus, unchanged in XYZ, runs from lightness 152 to lightness 16 as the surround is raised — and only the bottom of that range has a name.

brain · Appearance

Named alongside it

The objects these essays reach for when they reach for this one.

CIECAM16Colour appearanceColourfulnessLightnessAccessibilityColour constancyContrast ratioLuminanceLuminous efficiencyNamingPhotometrySimultaneous contrast

All concepts