Luminance Luminance Li people Category="Photometry"Category="Physical quantity"Category="Video and movie technology"Luminance (also called luminosity) is a photometric measure of the density of Luminous intensity in a given direction. The SI unit for luminosity is Candela per square meter.

SI photometry units
Quantity SI unit Symbol Notes
Luminous energy lumen seconds lm · s lumen seconds are sometimes called Talbots
Luminous flux lumen or (candela · Steradian) lm also called luminous power
Luminous intensity Candela or (lumen / steradian) cd
Luminance candela / Square metre cd/m² also called luminosity
Illuminance Lux or (lumen / square metre) lx
Luminous efficacy lumens per Watt lm/W maximum possible (@ 555 nm) is 683

SI photometry units
Quantity	SI unit	Symbol	Notes
Luminous energy	lumen seconds	lm · s	lumen seconds are sometimes called Talbots
Luminous flux	lumen or (candela · Steradian)	lm	also called luminous power
Luminous intensity	Candela or (lumen / steradian)	cd
Luminance	candela / Square metre	cd/m²	also called luminosity
Illuminance	Lux or (lumen / square metre)	lx
Luminous efficacy	lumens per Watt	lm/W	maximum possible (@ 555 nm) is 683

In television

As applied to Analog television signals, two different words are used, luminance and luma, meaning two different things. Luma is a new word proposed by the NTSC in 1953 to prevent confusion between the Y' component of a color signal and the traditional meaning of luminance. While luminance is the weighted sum of the linear RGB components of a color video signal, proportional to intensity, luma is the weighted sum of the non linear R'G'B' components after Gamma correction has been applied, and thus is not the same as either intensity or luminance.

An incorrect luma setting can cause visible flicker in a television display.

For Standard-definition television systems using older phosphor characteristics modeling for the RGB primaries, (non-linear) luma can be calculated from gamma-adjusted RGB using the CCIR 601 formula Y' = 0.299 R' + 0.587 G' + 0.114 B'. Modern HDTV systems use a different definition of RGB phosphor characteristics and the ITU-R BT.709 formula Y' = 0.2126 R' + 0.7152 G' + 0.0722 B'. In both formulas, scaling and offsets used on both sides of the equation are assumed to be the same (e.g., ranging from 16 for black to 235 for white when used for Digital video such as CCIR 601). Otherwise, some adjustments to the formula are needed to account for different scaling and offsets.

In television

See also