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C.P. \^ittingham and P.M. Bishop 



660 670 680 690 700 

 Wavelength of Background llgbt in 1141 



Figure 2 Percentage increase in yield for a monochromatic flash 

 as a function of the wavelength of the continuous background 

 light. The percentage is expressed as the increase in yield 

 compared to a flash given in darkness. The upper figure was 

 obtained with a 697 mp flash, the lower with a 644 rap flash. 



a second region from 671 to 683 m;j has a sharp peak at 675 mp. 

 Beyond 685 mp, and in the trough between the two peaks, the addi- 

 tion of background light appears to have little influence on the 

 yield of the flash. 



The results from the converse experiment, using a 644 mu 

 flash are shown in figure 2. Here also there are two regions 

 where the background light is effective in enhancing the yield 

 from the flash. These extend from 670 to 678 mp, with a sharp 



