16 



Table 1 (concluded) 

 CONVERSION FACTORS 



O. Illumination, brightness, etc.: (continued) 

 1 phot (ph.) 



= 1 lumen incident per 

 square centimeter 

 1 stilb (sb.) 



= 1 Int. c. cm." 2 



= it L. = 3.142 L. 



= 2919 ft.-L. 

 1 lambert (L.) 



= 1/tt sb. = 0.3183 sb. 



= 2.054 c. in." 2 



= 929 ft.-L. 

 1 millilambert (mL.) 



= 10- 8 L. 

 1 apostilb, in International units 



1 



1 candle per in. 2 (c. in. -2 ) 



= 0.1550 sb. 



= 0.487 L. 



= 452.4 ft.-L. 

 1 footlambert (ft.-L.) 



= 0.0003426 sb. 



= 0.001076 L. 



= 0.002211 c. in." 2 

 1 candle per ft. 2 



= 3.142 ft.-L. 



.1/(,XW)*- „ 

 = 0.1 mL. 

 1 apostilb, in German (Hefner) 

 units 



= 0.09 mL. 



stilb 



Luminous efficiency: At wave length of maximum luminosity 0.555 n for 

 photopic vision, the luminous efficiency is 680 lumens per watt, corresponding to a 

 minimum "mechanical equivalent of light" of 0.00151 watt per lumen. 



SMITHSONIAN METEOROLOGICAL TABLES 



