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Lambert (unit)

The lambert (symbol L[1][2]) 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

Units of luminance
cd/m2 (SI unit)
≡ nit ≡ lm/m2/sr 		stilb (sb) (CGS unit)
≡ cd/cm2 		apostilb (asb)
≡ blondel 		bril skot (sk) lambert (L) foot-lambert (fL)
= 1 ⁄ π cd/ft2
1 cd/m2 = 1 10−4 π
≈ 3.142 		107 π
≈ 3.142×107 		103 π
≈ 3.142×103 		10−4 π
≈ 3.142×10−4 		0.30482 π
≈ 0.2919
1 sb = 104 1 104 π
≈ 3.142×104 		1011 π
≈ 3.142×1011 		107 π
≈ 3.142×107 		π
≈ 3.142 		30.482 π
≈ 2919
1 asb = 1 ⁄ π
≈ 0.3183 		10−4 ⁄ π
≈ 3.183×10−5 		1 107 103 10−4 0.30482
≈ 0.09290
1 bril = 10−7 ⁄ π
≈ 3.183×10−8 		10−11 ⁄ π
≈ 3.183×10−12 		10−7 1 10−4 10−11 0.30482×10−7
≈ 9.290×10−9
1 sk = 10−3 ⁄ π
≈ 3.183×10−4 		10−7 ⁄ π
≈ 3.183×10−8 		10−3 104 1 10−7 0.30482×10−3
≈ 9.290×10−5
1 L = 104 ⁄ π
≈ 3183 		1 ⁄ π
≈ 0.3183 		104 1011 107 1 0.30482×104
≈ 929.0
1 fL = 1 ⁄ 0.30482 ⁄ π
≈ 3.426 		1 ⁄ 30.482 ⁄ π
≈ 3.426×10−4 		1 ⁄ 0.30482
≈ 10.76 		107 ⁄ 0.30482
≈ 1.076×108 		103 ⁄ 0.30482
≈ 1.076×104 		10−4 ⁄ 0.30482
≈ 1.076×10−3 		1

See also

Other units of luminance:

SI photometry quantities
Quantity Unit Dimension
[nb 1] 		Notes
Name Symbol[nb 2] Name Symbol
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 steradian) 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−2⋅J 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−2⋅J Luminous flux incident on a surface
Luminous exitance, luminous emittance Mv lumen per square metre lm/m2 L−2⋅J Luminous flux emitted from a surface
Luminous exposure Hv lux second lx⋅s L−2⋅T⋅J Time-integrated illuminance
Luminous energy density ωv lumen second per cubic metre lm⋅s/m3 L−3⋅T⋅J
Luminous efficacy (of radiation) K lumen per watt lm/W M−1⋅L−2⋅T3⋅J Ratio of luminous flux to radiant flux
Luminous efficacy (of a source) η[nb 3] lumen per watt lm/W M−1⋅L−2⋅T3⋅J Ratio of luminous flux to power consumption
Luminous efficiency, luminous coefficient V 1 Luminous efficacy normalized by the maximum possible efficacy
See also:
  1. ^ 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.
  2. ^ 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
  3. ^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ for luminous efficacy of a source.

References

  1. ^ "lambert". Illuminating Engineering Society. Retrieved 2024-11-05.
  2. ^ "Luminance | Photometric Brightness | Nit | Stilb | Apostilb | Blondel | Lambert | Footlambert | Skot". www.schorsch.com. Retrieved 2024-11-05.
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