Dictionary:

lambert

  (lăm'bərt)

The unit of brightness in the centimeter-gram-second system, equivalent to the brightness of a perfectly diffusing surface that emits or reflects one lumen per square centimeter.

[After Johann Heinrich Lambert (1728–1777), German physicist and astronomer.]

[Etymology: J. H. Lambert; Germany 1728-77] luminance, irradiance. Symbol L. Metric-c.g.s. 1920 For a point on a diffuser, identically candela·steradian per square centimetre = cd·sr·cm^-2, = 10⁴ cd·sr·m^-2 = 10⁴ lm·m^-2. (The corresponding m.k.s. unit was the apostilb, = 10^-4 L. There is no corresponding specially named unit in the SI, but the lux or illuminence has the same basic dimensions as the apostilb.) For a perfect diffuser, 1 L corresponds to the emission of ¹/_4π cd·cm^-2, = 0.318 3~ cd·cm^-2, = 0.318 3~ stilb. The millilambert (mL) was usual.

A unit of luminance equal to (1/π) candela per sq cm; equal to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of 1 lumen per sq cm. Abbr. L.

The noun has one meaning:

Meaning #1: a cgs unit of illumination equal to the brightness of a perfectly diffusing surface that emits or reflects one lumen per square centimeter
  Synonym: L