Lambert (unit)
The lambert (symbol L, la or Lb) 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).
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[nb 2] | ||||
| Luminous energy | Qv[nb 3] | lumen second | lm⋅s | T J | The lumen second is sometimes called the talbot. | |||
| Luminous flux, luminous power | Φv[nb 3] | lumen (= candela steradians) | lm (= cd⋅sr) | J | Luminous energy per unit time | |||
| Luminous intensity | Iv | candela (= lumen per steradian) | cd (= lm/sr) | J | Luminous flux per unit solid angle | |||
| Luminance | Lv | candela per square metre | cd/m2 (= lm/(sr⋅m2)) | L−2J | Luminous flux per unit solid angle per unit projected source area. The candela per square metre is sometimes called the nit. | |||
| Illuminance | Ev | lux (= lumen per square metre) | lx (= lm/m2) | L−2J | Luminous flux incident on a surface | |||
| Luminous exitance, luminous emittance | Mv | lumen per square metre | lm/m2 | L−2J | Luminous flux emitted from a surface | |||
| Luminous exposure | Hv | lux second | lx⋅s | L−2T J | Time-integrated illuminance | |||
| Luminous energy density | ωv | lumen second per cubic metre | lm⋅s/m3 | L−3T J | ||||
| Luminous efficacy (of radiation) | K | lumen per watt | lm/W | M−1L−2T3J | Ratio of luminous flux to radiant flux | |||
| Luminous efficacy (of a source) | η[nb 3] | lumen per watt | lm/W | M−1L−2T3J | Ratio of luminous flux to power consumption | |||
| Luminous efficiency, luminous coefficient | V | 1 | Luminous efficacy normalized by the maximum possible efficacy | |||||
| See also: SI · Photometry · Radiometry | ||||||||
- Standards organizations recommend that photometric quantities be denoted with a subscript "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
- The symbols in this column denote dimensions; "L", "T" and "J" are for length, time and luminous intensity respectively, not the symbols for the units litre, tesla and joule.
- Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ for luminous efficacy of a source.
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