Brightness

Brightness is the perceived intensity of light emitted or reflected by a surface. It depends on the light reaching the eye and on visual adaptation.

Luminance: Luminance is the photometric measure of light emitted or reflected in a given direction per unit area. It quantifies the light stimulus that often contributes to perceived brightness, though the two are not identical.
Photometry: Photometry measures light according to the spectral sensitivity of human vision. Brightness is perceptual, while photometry provides standardized measurements related to visual sensitivity.
Lightness: Lightness is the perceived reflectance of a surface, judged relative to a white reference under an illuminant. Brightness describes perceived intensity, whereas lightness concerns how much light a surface seems to reflect.
Brightness temperature: Brightness temperature is the temperature a blackbody would need to produce a measured radiation intensity at a given frequency. In radio astronomy, measured brightness is expressed as an equivalent temperature rather than ordinary visual appearance.
Visual adaptation: Visual adaptation is the adjustment of the visual system’s sensitivity to prevailing illumination. The same luminance can appear different in brightness after the eye adapts to different light levels.
Radiometry: Radiometry measures electromagnetic radiation in physical units without weighting it by human vision. It distinguishes physical radiant energy from the visually weighted quantities associated with brightness.
Colorfulness: Colorfulness is the perceived degree to which a color appears chromatic rather than achromatic. A color can be highly bright without being highly colorful, or colorful without appearing especially bright.
High dynamic range: High dynamic range imaging represents a wider range of scene luminances than conventional imaging can display directly. It addresses how displays and images reproduce scenes containing both very bright and very dark regions.
Weber–Fechner law: The Weber–Fechner law models perceived changes in sensation as proportional to relative changes in stimulus intensity. It captures why equal physical increases in light do not produce equal perceived brightness increments.
Illuminance: Illuminance is the luminous flux incident on a surface per unit area. It describes the light falling on a surface, which influences reflected light and its perceived brightness.

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