NEW FLASHING LIGHT EXPERIMENTS 1477 



ruption of illumination could be acliieved by placing another batch of algae 

 in the path of the light while the first one is "digesting" the flash products 

 in darkness, E/« > 1 would mean also E/b > 1, i. e., an increase in the utili- 

 zation of solar energy (since, now, no hght energy will be wastefully ab- 

 sorbed by black screens). 



If the Emerson-Arnold reaction were the only one determining the inter- 

 mittency effect, the maximum improvement in the efficiency of hght utiliza- 

 tion could be expected with hght periods lasting just long enough to excite — 

 with the available hght intensity — one chlorophyll molecule out of between 

 250 and 2000 (to put all the enzyme Eb to work at the end of the flash), 

 and dark periods lasting long enough to permit the Emerson-Arnold reac- 

 tion to run to practical completion at the prevaihng temperature, but short 

 enough to avoid induction losses afterwards. According to p. 838, in 

 direct sunlight at noon ('-^85 klux), a directly exposed chlorophyll molecule 

 absorbs a photosynthetically effective quantum about once every 0.08 

 second. Therefore, one molecule in 2000 will absorb a quantum in a flash 

 of direct sunlight 40 ^sec. long, and one molecule in 250, in a flash of 300 

 fjLsec. duration. The dark period will have to last > 30 ^sec. (at 15-20° C.) 

 to complete the Emerson-Ai'nold reaction. Finite optical density of a 

 cell suspension will make the required length of the flash longer than 40- 

 300 /xsec; while the above-discussed (but not definitely understood) capac- 

 ity of dark intervals ^ 0.03 sec. to enhance the yield of such "milHsecond 

 flashes," may shift the optimum towards dark intervals much longer than 

 3000 Msec. 



Empirical studies of energy conversion yield as function of the "intermit- 

 tency pattern" have been carried out on optically thin layers of Chlorella 

 suspensions in connection with mass culturing of these algae, by Kok (1953) 

 and Myers and coworkers (1953, 1954). Kok used rotating sectors which 

 could be adjusted in width (varying tf/ta) and in speed of rotation (varying 

 both tf and ta in the same proportion) . The curves given in his paper show 

 that with a ratio ta/t/ = 4.5, a yield practically equal to that in constant 

 hght of the same intensity could be achieved in artificial light of about 70 

 klux at 1500 r.p.m., (z. e., tf = S msec, ta = 13.5 msec). If this intermit- 

 tency regime could be achieved by turbulent flow in a Chlorella suspension 

 (instead of by wasteful black sectors), the gain in energy conversion (com- 

 pared to nonstirred suspensions) would be by a factor of about 5. Since 

 these cells were grown indoors and showed saturation in constant light at 

 about 7 klux, still higher intermittency enhancement factors could be ex- 

 pected to result from an increase in the ratio tg/tf above 10 (so as to reduce 

 the average intensity of flashing illumination below the steady saturating 

 intensity) . In fact, yields not significantly diff"erent from those in continu- 

 ous hght could be obtained, with such "indoor" cells, at ta c^ 100 msec. 



