178 Tables 156-158. 



SENSITIVENESS OF THE EYE TO RADIATION. 



(Compiled from Nutting, Bulletin of the Bureau of Standards.) 

 Radiation is easily visible to most eyes from 0.330/ti in the violet to o.yjofi in the red. At low 

 intensities approaching threshold values (red vision) the maximum of spectral sensibility lies 

 in the green at about 0.510^1 for 90% of all persons. At higher intensities with the establish- 

 ment of cone vision the maximum shifts towards the yellow at least as far as 0.560/x. 



TABLE 166. —Variation of the Sensitiveness of the Eye with the Wave-length at Low Intensities (near 



Threshold Values). Eonlg. 



TABLE 157. — Variation of Sensitiveness to Radiation of Greater Intensities. 



The sensibility is approximately proportional to the intensity over a wide range. The ratio of 

 optical- to radiation-intensity increases more rapidly for the red than for the blue or green 

 (Purkinje phenomenon). 



The intensity is given for the spectrum at 0.535/1 (green). 



TABLE 158. — Sensibility to Small Differences In Intensity measured as a Fraction of the Whole. 



The sensibility to small differences in inten- 

 sity is independent of the intensity (Fech- 

 ner's law). About 0.016 for moderate 

 intensities. Greater for extreme values. 



It is independent of wave-length, extremes 

 excepted (Konig's law). 



Sensibility to slight differences in wave- 

 length has two pronounced maxima (one 

 in the yellow, one in the green) and two 

 slight maxima (extreme blue, extreme 

 red). 



The visual sensation as a function of the 

 time approaches aconstant value with the 

 lapse of time. With blue light there 

 seems to be a pronoimced maximum at 

 0.07 sec, with red a slight one at 0.12 sec- 

 onds, with green the sensation rises stead- 

 ily to its final value. For lower intensi- 

 ties these max. occur later. 



An intensity of 500 metre-candles is about 

 that on a horizontal plane on a cloudy 

 day. 



Smithsonian Tables. 



