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/m).
Definition
1 lambert (L) = candela per square centimetre (0.3183 cd/cm) or cd m
| cd/m (SI unit) ≡ nit ≡ lm/m/sr |
stilb (sb) (CGS unit) ≡ cd/cm |
apostilb (asb) ≡ blondel |
bril | skot (sk) | lambert (L) | foot-lambert (fL) = 1 ⁄ π cd/ft | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1 cd/m | = | 1 | 10 | π ≈ 3.142 |
10 π ≈ 3.142×10 |
10 π ≈ 3.142×10 |
10 π ≈ 3.142×10 |
0.3048 π ≈ 0.2919 | ||
| 1 sb | = | 10 | 1 | 10 π ≈ 3.142×10 |
10 π ≈ 3.142×10 |
10 π ≈ 3.142×10 |
π ≈ 3.142 |
30.48 π ≈ 2919 | ||
| 1 asb | = | 1 ⁄ π ≈ 0.3183 |
10 ⁄ π ≈ 3.183×10 |
1 | 10 | 10 | 10 | 0.3048 ≈ 0.09290 | ||
| 1 bril | = | 10 ⁄ π ≈ 3.183×10 |
10 ⁄ π ≈ 3.183×10 |
10 | 1 | 10 | 10 | 0.3048×10 ≈ 9.290×10 | ||
| 1 sk | = | 10 ⁄ π ≈ 3.183×10 |
10 ⁄ π ≈ 3.183×10 |
10 | 10 | 1 | 10 | 0.3048×10 ≈ 9.290×10 | ||
| 1 L | = | 10 ⁄ π ≈ 3183 |
1 ⁄ π ≈ 0.3183 |
10 | 10 | 10 | 1 | 0.3048×10 ≈ 929.0 | ||
| 1 fL | = | 1 ⁄ 0.3048 ⁄ π ≈ 3.426 |
1 ⁄ 30.48 ⁄ π ≈ 3.426×10 |
1 ⁄ 0.3048 ≈ 10.76 |
10 ⁄ 0.3048 ≈ 1.076×10 |
10 ⁄ 0.3048 ≈ 1.076×10 |
10 ⁄ 0.3048 ≈ 1.076×10 |
1 | ||
See also
Other units of luminance:
| Quantity | Unit | Dimension |
Notes | ||
|---|---|---|---|---|---|
| Name | Symbol | Name | Symbol | ||
| Luminous energy | Qv | lumen second | lm⋅s | T⋅J | The lumen second is sometimes called the talbot. |
| Luminous flux, luminous power | Φv | 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/m (= lm/(sr⋅m)) | L⋅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/m) | L⋅J | Luminous flux incident on a surface |
| Luminous exitance, luminous emittance | Mv | lumen per square metre | lm/m | L⋅J | Luminous flux emitted from a surface |
| Luminous exposure | Hv | lux second | lx⋅s | L⋅T⋅J | Time-integrated illuminance |
| Luminous energy density | ωv | lumen second per cubic metre | lm⋅s/m | L⋅T⋅J | |
| Luminous efficacy (of radiation) | K | lumen per watt | lm/W | M⋅L⋅T⋅J | Ratio of luminous flux to radiant flux |
| Luminous efficacy (of a source) | η | lumen per watt | lm/W | M⋅L⋅T⋅J | Ratio of luminous flux to power consumption |
| Luminous efficiency, luminous coefficient | V | 1 | Luminous efficacy normalized by the maximum possible efficacy | ||
| See also: | |||||
- 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.
- 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
- ^ Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ for luminous efficacy of a source.
References
- "lambert". Illuminating Engineering Society. Retrieved 2024-11-05.
- "Luminance | Photometric Brightness | Nit | Stilb | Apostilb | Blondel | Lambert | Footlambert | Skot". www.schorsch.com. Retrieved 2024-11-05.