Re: (Lambert with feet!) Tdigest 9

[T3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxxxx>]

RE: John B. adds a ps wondering if Lambert has feet like a duck? (Or 
maybe related to Howard the Duck?).
  I may have put my foot in it here. It seems a real Lambert is "the 
brightness of a surface emitting or reflecting one lumen per square 
centimeter." Thus John asks where's the beef, er..foot? 
Well, early Americans called Illumination Engineers, who hated 
metric, invented the Ft.-Lambert, Symbol B-1 to describe a surface 
which has a brightness equal to the uniform brightness of a perfectly 
diffusing surface emitting or reflecting one lumen per square foot!
(1 lambert=929 footlamberts)

Why did they do this? Since they run around measuring foot-candles 
with their meters (incident light) they can muliply this by the 
refection factor of the surface and voila they have ft-lamberts.

        Ft-L  = Lumens (incident) x reflection factor divided by area 
                    in square feet of the surface
 I haven't thought about this in a long time, but this may have been 
replaced by stilbs and lux by now? Or maybe we are like Canada
who went half metric where dealers roll out metric lengths of rug 
material yards wide as it comes from the mills in USA. :-)
BobH


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