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
Units of luminance
v
t
e
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
107π ≈ 3.142×107
103π ≈ 3.142×103
10−4π ≈ 3.142×10−4
0.30482π ≈ 0.2919
1 sb
=
104
1
104π ≈ 3.142×104
1011π ≈ 3.142×1011
107π ≈ 3.142×107
π ≈ 3.142
30.482π ≈ 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
^"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.
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