350 



HENRY LAURENS AND HENRY D. HOOKER, JR. 



action of the light will not be effective until it has reached a 

 certain minimum. To the production of this minimal photo- 

 chemical effect a certain fixed amount of energy is necessary. 

 The minimal duration of exposure below which no effect is pro- 

 duced is an indication of the physiological intensity, or stimu- 



TABLE 1 



The relative stimulating value of spectral lights of equal energy content as ascer- 

 tained from, the determination of the minimal duration of exposure necessary to 

 produce a reaction 



lating value, of the light. The relative stimulating value may 

 be ascertained by taking the reciprocal of the presentation time, 

 since this represents the time necessary to produce a constant 

 quotient of change and since all the lights are of equal physical 

 intensity. These values are shown in column 4 of table 1. For 

 plotting, the relative stimulating efficiencies are expressed as 



