Decreasing brightness with depth (underwater photo as example)

Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light.[1] In other words, brightness is the perception elicited by the luminance of a visual target. It is not necessarily proportional to luminance. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models. Brightness refers to an absolute term and should not be confused with lightness.[2]

The adjective bright derives from an Old English beorht with the same meaning via metathesis giving Middle English briht. The word is from a Common Germanic *berhtaz, ultimately from a PIE root with a closely related meaning, *bhereg- "white, bright". "Brightness" was formerly used as a synonym for the photometric term luminance and (incorrectly) for the radiometric term radiance. As defined by the US Federal Glossary of Telecommunication Terms (FS-1037C), "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light.[3]

A given target luminance can elicit different perceptions of brightness in different contexts; see, for example, White's illusion.

In an RGB color space, brightness can be thought of as the arithmetic mean μ of the red, green, and blue color coordinates (although some of the three components make the light seem brighter than others, which, again, may be compensated by some display systems automatically[clarification needed]):[4]

Brightness is also a color coordinate in HSL color space : hue, saturation, and lightness, meaning here brightness.

With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude.

Brightness is, at least in some respects, the antonym of darkness.

  1. ^ Merriam-Webster Dictionary definition of bright
  2. ^ [1] Brightness vs. Lightness
  3. ^ Brightness” in Federal Standard 1037C, the Federal Glossary of Telecommunication Terms (1996)
  4. ^ What are HSB and HLS?, Charles Poynton: "The usual formulation of HSB and HLS compute so-called "lightness" or "brightness" as (R + G + B)/3. This computation conflicts badly with the properties of colour vision, as it computes yellow to be about six times more intense than blue with the same "lightness" value (say L = 50)."