apostilb

(optics) A luminance unit equal to one ten-thousandth of a lambert. Also known as blandel.

[Etymology: Gk: ‘away’ + ‘glitter’] (blondel) luminance, irradiance. Symbol asb. Metric-m.k.s. The name for a point on a diffuser, identically candela·steradian per square metre, = cd·sr·m^-2. (There is no corresponding specially named unit in the SI, but the lux for illuminence is basically the same as the apostilb.) For a perfect diffuser, 1 asb corresponds to the emission of ¹/_π cd·m^-2 = 0.3183~ cd·m^-2. The corresponding c.g.s. unit was the lambert, = 10⁴ asb.

A unit of luminance equal to (1/π) candela per square meter.