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# Stilb (unit)

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terms such as candle per square inch and candle per square meter were more common.[2] The unit has since largely been replaced by the SI unit: candela per square meter.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

\mathrm{1\, \frac{cd}{m^2} = 10^{-4}\, sb}

\mathrm{1\, sb = 1\,\frac{cd}{cm^2} = 10^4\,\frac{cd}{m^2}}

\mathrm{1 \, sb = 10^4 \, nit = 10^7 \, millinit}

\mathrm{1 \, sb = 1 \pi \, L = 10^3 \pi \, mL = 10^4 \, \pi \, asb = 10^4 \pi \, blondel = 10^7 \pi \, sk = 10^{11} \pi \, bril}

\mathrm{1 \, sb = 10^4\,\frac{cd}{m^2} \approx 0.3048^2 \cdot 10^4 \cdot \pi \,\, fL = 2918.6...\, fL}

Other units of luminance:

SI photometry quantities
Quantity Unit Dimension Notes
Name Symbol[nb 1]r Name Symbol Symbol
Luminous energy Qv [nb 2] lumen second lm⋅s TJ [nb 3] Units are sometimes called talbots.
Luminous flux / Luminous power Φv [nb 2] lumen (= cd⋅sr) lm J [nb 3] Luminous energy per unit time.
Luminous intensity Iv candela (= lm/sr) cd J [nb 3] Luminous power per unit solid angle.
Luminance Lv candela per square metre cd/m2 L−2J Luminous power per unit solid angle per unit projected source area. Units are sometimes called nits.
Illuminance Ev lux (= lm/m2) lx L−2J Luminous power incident on a surface.
Luminous exitance / Luminous emittance Mv lux lx L−2J Luminous power emitted from a surface.
Luminous exposure Hv lux second lx⋅s L−2TJ
Luminous energy density ωv lumen second per cubic metre lm⋅s⋅m−3 L−3TJ
Luminous efficacy η [nb 2] lumen per watt lm/W M−1L−2T3J Ratio of luminous flux to radiant flux or power consumption, depending on context.
Luminous efficiency / Luminous coefficient V 1
1. ^ photon quantities. For example: USA Standard Letter Symbols for Illuminating Engineering USAS Z7.1-1967, Y10.18-1967
2. ^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
3. ^ a b c "J" here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.

## Notes and references

• Stilb at A Dictionary of Units of Measurement, Russ Rowlett and the University of North Carolina at Chapel Hill. Accessed June 2008.
• Stilb at Sizes.com. Accessed June 2008.
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.
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