The apostilb is an obsolete unit of luminance.
[1] The SI unit of luminance is the candela per square metre (cd/m2).
In 1942 Parry Moon proposed to rename the apostilb the blondel, after the French physicist André Blondel.
[2] The symbol for the apostilb is asb.
The apostilb is defined in terms of another unit of luminance, the stilb (sb):