48 



DELAYED LIGHT PRODUCTION 



of a photomultiplier which measures the intensity S of the delayed 

 Hght. 



It is found that if T is smaller than a few hundreths of a second, 

 then S is a function of the product IT, that is, S depends only on 

 total energy E in the light flash. 



26-1 



1 1 r 



14 18 22 



relative light intensity 

 Fig. 1. 



Figure 2 gives the result of the experiment. The insert gives the 

 beginning of the curve for energies expressed as quanta per square 

 centimeter for light of wavelength approximately 6500 A. 



Let us assume that the saturation shown by the curve is due to 

 exhaustion of some substance K, and that the light changes K into 

 KB. The return of KB to K generates the excited chlorophyll which 

 emits the delayed light. 



Let X = amount of K at any time 



.Yo = amount of A' at the beginning of flash 

 a ^ cross section for the reaction K -^ KB 

 k — constant. 



We further assume that S, the delayed light intensity at the end of 

 the flash, is given by k times the amount of KB, that is, by 



