en 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.^[1] 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terms such as candle per square inch and candle per square meter were more common.^[2] The unit has since largely been replaced by the SI unit: candela per square meter.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.^[3]

Unit conversion

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	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

SI photometry quantities
v
t
e
Quantity		Unit		Dimension ^{[nb 1]}	Notes
Name	Symbol^{[nb 2]}	Name	Symbol	Dimension ^{[nb 1]}	Notes
Luminous energy	$Q v$ ^{[nb 3]}	lumen second	lm⋅s	T⋅J	The lumen second is sometimes called the talbot.
Luminous flux, luminous power	$Φ v$ ^{[nb 3]}	lumen (= candela steradian)	lm (= cd⋅sr)	J	Luminous energy per unit time
Luminous intensity	$I v$	candela (= lumen per steradian)	cd (= lm/sr)	J	Luminous flux per unit solid angle
Luminance	$L v$	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	$E v$	lux (= lumen per square metre)	lx (= lm/m²)	L⁻²⋅J	Luminous flux incident on a surface
Luminous exitance, luminous emittance	$M v$	lumen per square metre	lm/m²	L⁻²⋅J	Luminous flux emitted from a surface
Luminous exposure	$H v$	lux second	lx⋅s	L⁻²⋅T⋅J	Time-integrated illuminance
Luminous energy density	$ω v$	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: SI Photometry Radiometry

^ 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.

References

^ 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."
^ American Standard Definitions of Electrical Terms, New York: American Institute of Electrical Engineers, 1941.
^ 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.

Stilb (unit)

Unit conversion

See also

References

Further reading