# Lambert (unit)

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The lambert (symbol L, la or Lb) is a non-SI unit of luminance named for Johann Heinrich Lambert (1728–1777), a Swiss mathematician, physicist and astronomer. A related unit of luminance, the foot-lambert, is used in the lighting, cinema and flight simulation industries. The SI unit is the candela per square metre (cd/m²).

## Definition

1 lambert (L) = $\frac{1}{\pi}$ candela per square centimetre (0.3183 cd/cm²) or $\frac{10^4}{\pi}$ cd m-2

## See also

Other units of luminance:

SI photometry units
QuantitySymbol[nb 1]SI unitSymbolDimensionNotes
Luminous energyQv [nb 2]lumen secondlm⋅sT⋅J [nb 3]units are sometimes called talbots
Luminous fluxΦv [nb 2]lumen (= cd⋅sr)lm[nb 3]also called luminous power
Luminous intensityIvcandela (= lm/sr)cd[nb 3]an SI base unit, luminous flux per unit solid angle
LuminanceLvcandela per square metrecd/m2L−2⋅Junits are sometimes called nits
IlluminanceEvlux (= lm/m2)lxL−2⋅Jused for light incident on a surface
Luminous emittanceMvlux (= lm/m2)lxL−2⋅Jused for light emitted from a surface
Luminous exposureHvlux secondlx⋅sL−2⋅T⋅J
Luminous energy densityωvlumen second per metre3lm⋅sm−3L−3⋅T⋅J
Luminous efficacyη [nb 2]lumen per wattlm/WM−1⋅L−2⋅T3⋅Jratio of luminous flux to radiant flux
Luminous efficiencyV1also called luminous coefficient
See also: SI · Photometry · Radiometry
1. ^ Standards organizations recommend that photometric quantities be denoted with a suffix "v" (for "visual") to avoid confusion with radiometric or photon quantities.
2. ^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
3. ^ a b c "J" is the recommended symbol for the dimension of luminous intensity in the International System of Units.