{{short description|Unit of luminance}} The '''apostilb''' is an obsolete unit of luminance.<ref name=IPS>{{cite web |url=http://www.perimetry.org/index.php/publications/141-general/799-1978-ips-perimetry-standards |title=IPS Perimetric Standards, 1978 |publisher=Imaging and Perimetry Society |date=1978}}</ref> The SI unit of luminance is the candela per square metre (cd/m<sup>2</sup>). In 1942 Parry Moon proposed to rename the apostilb the '''blondel''', after the French physicist André Blondel.<ref>{{cite journal |first=Parry |last=Moon |title=A system of photometric concepts |journal=Journal of the Optical Society of America |volume=32 |issue=6 |page=356 |date=June 1942 |doi=10.1364/JOSA.32.000348 |quote=The unit is pi times the lumens per square meter per steradian. Such a name is impossibly cumbersome, so a new name is proposed, the blondel, after André Blondel who did pioneer work in photometric nomenclature.|bibcode=1942JOSA...32..348M }}</ref> The symbol for the apostilb is '''asb'''.

The apostilb is defined in terms of another unit of luminance, the stilb (sb): :1 asb = 1/{{pi}} ⋅ 10<sup>−4</sup> sb :{{pi}} asb = 1 cd/m<sup>2</sup> {{luminance conversions}}

==Table of SI photometry quantities for reference== {{SI light units}} ==See also== Other units of luminance: <!-- in order of relevance in regard to apostilb --> * Lambert&nbsp;(L) * Skot&nbsp;(sk) * Bril&nbsp;(bril) * Nit&nbsp;(nit) * Foot-lambert&nbsp;(fL)

==References== {{reflist}}

Category:Units of luminance Category:Centimetre–gram–second system of units