156 



BIOPHYSICALLY ACTIVE LIGHT 



that the cell is most sensitive to yellow light of wavelength 5800 A, 

 while the eye's sensitivity as shown by the dotted curve is in the yellow- 

 green at 5560 A. Note, however, how much more sensitive it is in the 

 blue than the eye. 



Fig. IV-15. Weston photronic photoelectric cell and its component parts, 

 Model 594. (By courtesy of Weston Electrical Instrument Corporation.) 



Should it be desirable to use such a cell to simulate the human eye, it 

 will be necessary to place a special filter, made for this purpose, over 

 the cell so as to absorb the radiant energy represented by the area between 

 the visibility curve and sensitivity curve of the cell. 



„ 90 



300 400 , 500 i /500 . 



Ultra violetl f I Blue I Green If' \ I Red 

 Violet Yellow Orange 



700 x 10" 7 cm=X 

 I Infra-red 



Fig. IV-16. Spectral sensitivity of the Weston photronic cell. (By courtesy of 

 Weston Electrical Instrument Corporation.) 



A typical example of the use of a photronic cell in a colorimeter is 

 fouDd in the instruments designed by Armstrong and Kuder [1935], or 

 that of Evelyn [1936]. The so-called Kuder Photoelectric Model 

 (Fisher Scientific Company) is a colorimeter operating with a direct- 



