The lambert (symbol L) is a non-SI metric 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).

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

Other units of luminance: