Gordon T. Uber
guber at netcom.com
Sun Jun 26 13:26:36 EST 1994
Per Allen Stimson "Photometry and Radiometry for Engineers",
John Wiley & Sons, 1974, p. 309 ff:
Ev = log2 (ES/C)
Ev = Exposure Value
E = scene illumination in foot candles
S = film speed
C = constant = 22 +/- 7 for 35 mm cameras and larger
American National Standard, General-Purpose Photographic Exposure Meteres
(Photoelectric Type), Ph3.49,
American National Standards Institute, New York.
Caution: The human eye and light meters (by definition) respond most
strongly to yellow-green light (555 nm). Plants respond most to red and
blue light. Hence the spectral distribution (color) of the light may
need to be taken into account.
Hope this helps.
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