44 



PHOTOCHEMICAL PRINCIPLES 



2000 



2200 2400 2600 2800 



WAVELENGTH 



3000 



Fig. 2. Action spectra. Curve A, minimum energy values found for 

 optimal population density — log scale on right and inverse on left. This is 

 a close approach to an efficiency spectrum. Curve B, Values for small 

 population density (points at left of Fig. 1). This shows influence of both 

 absorption and efficiency. 



optimal value of cell density depends upon the total absorption per 

 cell and upon the stirring. Hence it occurs at a different cell density for 

 each wavelength. Thus, if we plot 1/A^ for the energy minimums, we 

 obtain a curve (Fig. 3) strongly resembling the total absorption. If we 

 plot the minimum energy against each wavelength, we obtain an action 

 spectrum (curve A, Fig. 2). All evidence of absorption has disap- 



2000 2200 2400 2600 2800 3000 



WAVELENGTH 



Fig. 3. Comparison of observed total absorption with the implied effec- 

 tive absorption B/A and reciprocal of optimal density 1/N. 



