Light measurement

Bill Williams bwilliam at
Wed Jul 5 10:58:41 EST 1995

Andy's conversions are good, but only for sunlight.  The units are not
directly convertible without knowing the spectrum of the light source. 
"Lux" and most of the other "old" light measurements (foot-candles,
etc.), are based on the response of the human eye and so weight yellow
photons particularly strongly.  Quantum meters (and plants, mostly!)
try to weight all photons in the 400-600 nm range equally.  Power
meters (W/m2) weight the photons depending on their energy, so blue
ones count more than red ones.  See if you can borrow a quantum probe
from somebody!
Bill Williams
bwilliam at
Dept. of Biology
St. Mary's College of Maryland
St. Mary's City, MD 20686 

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