Stilb (unit)

The stilb (sb) is the CGS unit of luminance for objects that are not self-luminous. It is equal to one candela per square centimeter or 104 nits (candelas per square meter). The name was coined by the French physicist André Blondel around 1920. It comes from the Greek word stilbein (στίλβειν), meaning 'to glitter'.

It was in common use in Europe up to World War I. In North America self-explanatory terms such as candle per square inch and candle per square meter were more common. The unit has since largely been replaced by the SI unit: candela per square meter. The current national standard for SI in the United States discourages the use of the stilb.

Unit conversion

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
≈ 2,919
1 asb = 1 ⁄ π
≈ 0.3183		 10−4 ⁄ π
≈ 3.183×10−5		 1 107 103 10−4 0.30482
≈ 0.0929
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
≈ 9.29×10−9
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
≈ 9.29×10−5
1 L = 104 ⁄ π
≈ 3,183		 1 ⁄ π
≈ 0.3183		 104 1011 107 1 0.30482×104
≈ 929
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

SI photometry quantities
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/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 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. 1 2 3 Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ for luminous efficacy of a source.

See also

References

  1. ↑ Parry Moon. "System of photometer concepts", in the Journal of the Optical Society of America, volume 32, number 6 (June 1942). – Page 355: "The lumen was proposed by Blondel in 1894 and is now universally accepted. The names, phot and stilb were likewise coined by Blondel (1921) and are in general use on the Continent."
  2. ↑ American Standard Definitions of Electrical Terms, New York: American Institute of Electrical Engineers, 1941.
  3. ↑ IEEE/ASTM SI 10-2002. American National Standard for Use of the International System of Units (SI): The Modern Metric System. New York: IEEE, 30 December 2002. See Section 3.3.3.

Further reading