Apostilb
The apostilb is an obsolete unit of luminance.[1] The SI unit of luminance is the candela per square metre (cd/m2). In 1942 Parry Moon proposed to rename the apostilb the blondel, after the French physicist André Blondel.[2] The symbol for the apostilb is asb.
The apostilb is defined in terms of another unit of luminance, the stilb (sb):
- 1 asb = 1/π ⋅ 10−4 sb
- π asb = 1 cd/m2
| 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 | ||
Table of SI photometry quantities for reference
[edit]
| 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: | |||||
- ^ 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
- ^ 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.
See also
[edit]Other units of luminance:
- Lambert (L)
- Skot (sk)
- Bril (bril)
- Nit (nit)
- Foot-lambert (fL)
References
[edit]- ^ "IPS Perimetric Standards, 1978". Imaging and Perimetry Society. 1978.
- ^ Moon, Parry (June 1942). "A system of photometric concepts". Journal of the Optical Society of America. 32 (6): 356. Bibcode:1942JOSA...32..348M. doi:10.1364/JOSA.32.000348.
The unit is pi times the lumens per square meter per steradian. Such a name is impossibly cumbersome, so a new name is proposed, the blondel, after André Blondel who did pioneer work in photometric nomenclature.