PHOTOGRAPHIC SENSITOMETRY 



159 



shows the variation in light output for various types of incandescent lamps for small 

 voltage fluctuations. 



.V 



L=Lo(vJ 



-Br 



300 



250 



§200 



S 150 



100 

 90 



60 



« 70 



60 



50 



^ 40 



30 



V ^^2 



F=Fo(^) 



P=Po(^^) 



I=Io(vJ 





70 80 90 100 125 



Per Cen+ of Normal Vol+age 



Fig. 4. — Variations of life (L), light output (i^), power consumption (P), and current con- 

 sumption (/) of tungsten lamps in terms of normal filament voltage. 



For simplicity in calculation without the use of tables, Eq. (6) may be expanded 

 by means of the binomial-expansion theorem. The first three terms of this expansion 

 are: 



+ ^ - +A -L (1 - B2W , (1 -^2)(1 -2B2W 



(7) 



The expansion of Eq. (7) is only valid for small values of b, in which case the series 



