Lambert (unit)
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) = 
candela per square centimetre (0.3183 cd/cm²) or 
cd m−2
See also
Other units of luminance:
| Quantity | Unit | Dimension | Notes | |||||
|---|---|---|---|---|---|---|---|---|
| Name | Symbol[nb 1] | Name | Symbol | Symbol | ||||
| Luminous energy | Qv [nb 2] | lumen second | lm⋅s | T⋅J [nb 3] | Units are sometimes called talbots. | |||
| Luminous flux / luminous power | Φv [nb 2] | lumen (= cd⋅sr) | lm | J [nb 3] | Luminous energy per unit time. | |||
| Luminous intensity | Iv | candela (= lm/sr) | cd | J [nb 3] | Luminous power per unit solid angle. | |||
| Luminance | Lv | candela per square metre | cd/m2 | L−2⋅J | Luminous power per unit solid angle per unit projected source area. Units are sometimes called nits. | |||
| Illuminance | Ev | lux (= lm/m2) | lx | L−2⋅J | Luminous power incident on a surface. | |||
| Luminous exitance / luminous emittance | Mv | lux | lx | L−2⋅J | Luminous power emitted from a surface. | |||
| Luminous exposure | Hv | lux second | lx⋅s | L−2⋅T⋅J | ||||
| Luminous energy density | ωv | lumen second per cubic metre | lm⋅s⋅m−3 | L−3⋅T⋅J | ||||
| Luminous efficacy | η [nb 2] | lumen per watt | lm/W | M−1⋅L−2⋅T3⋅J | Ratio of luminous flux to radiant flux or power consumption, depending on context. | |||
| Luminous efficiency / luminous coefficient | V | 1 | ||||||
| See also: SI · Photometry · Radiometry | ||||||||
- ↑ Standards organizations recommend that photometric quantities be denoted with a suffix "v" (for "visual") to avoid confusion with radiometric or photon quantities. For example: USA Standard Letter Symbols for Illuminating Engineering USAS Z7.1-1967, Y10.18-1967
- 1 2 3 Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
- 1 2 3 "J" here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.
References
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