88 



TABLE 59.— RELATIVE LUMINOSITY DATA FOR VARIOUS FIELD BRIGHTNESSES" 



(Logarithms of field brightness in first line) 



27 L. A. Jones, private communication. 

 * Average of Weaver and Hecht's values. 



TABLE 60.— BLANCHARD'S DATA RELATING INSTANTANEOUS 

 THRESHOLD TO FIELD BRIGHTNESS** 



Field bright- Instant; 



ness * thresh 



millilamberts 



100 1.9 X 



10 4.2 X 



1 8.9 X 



.1 1.9 X 



.032 8.9 X 



.01 4.2 X 



.0032 1.9 X 



.001 8.9 X 



.0001 1.9 X 



.00001 4.2 X 



•0 1.8 X 



** For reference, see footnote 25, p. 87. 



* The field brightnesses are values obtained by mechanically increasing or reducing values measured 

 at photopic levels. t Taken from smooth curve drawn through Blanchard's data. The unit will 



depend upon definition. As these figures stand they are brightnesses for this radiation measured at 

 photopic levels and reduced mechanically to values given. t For radiation from a source at a color 



temperature of 2680 °K. § This is the ratio of the eye sensitivity to that of the eye adapted to the 



next lower (one-tenth) field brightness for this radiation. || Minimum threshold from Taylor's value. 



SMITHSONIAN PHYSICAL TABLES 



