The apostilb is an old unit of luminance

Luminance

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...

, which was withdrawn from use in 1978. The SI

Si

Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

 unit of luminance is the candela per square metre (cd/m²). In 1942 it was proposed to rename the apostilb the blondel, after the French physicist André Blondel

André Blondel

André-Eugène Blondel was a French engineer and physicist. He is the inventor of the electromechanical oscillograph and a system of photometric units of measurement.-Life:...

. The symbol for the apostilb is asb.

The apostilb is defined in terms of another unit of luminance, the stilb

Stilb (unit)

The stilb 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 . The name was coined by the French physicist André Blondel around 1920. It comes from the Greek word stilbein meaning "to glitter".It was in common use in...

 (sb):

1 asb = 1/π · 10^-4 sb

3.14 asb = 1 cd/m²

See also

Other units of luminance:

• Lambert
  Lambert (unit)
  The lambert is a non-SI unit of luminance named for Johann Heinrich Lambert , a Swiss mathematician, physicist and astronomer. A related unit of luminance, the foot-lambert, is used in the lighting, cinema and flight simulation industries...
  
   (L)
• Skot (sk)
• Bril (bril)
• Nit
  Nit (unit)
  The candela per square metre is the derived SI unit of luminance. The unit is based on the candela, the SI unit of luminous intensity, and the square metre, the SI unit of area...
  
   (nit)
• Foot-lambert (fL)