INTERMITTENCY FACTOR IN FLASHING LIGHT 1447 



In saturating light, /? = 1, while i^ < 1, so that 4, is < 1. Thus, lEt can 

 only vary between 0.5 and 1 . 



We thus conclude that, if a certain amount of light energy is available 

 to be spent within a certain mterval of time, the best utilization of this 

 energy for photosynthesis can be achieved by spreading it uniformly over 

 the whole available period, rather than by using it in flashes. At least, 

 this must be the case ^vith ravid alternations of darkness and light. In the 

 mediMm range of alternations (one every minute) the same is obviously true 

 (because induction losses are the main intermittency effect in this range). 

 Only with slow alternations (e. g., one in several hours, or days) may there 

 be a chance of obtaining Iei factors higher than unity. 



These conclusions apply to the continuous or intermittent illumination 

 of the same plant, or the same cell in a suspension. Alternation can, how- 

 ever unprove the utilization of a continuous, uniform light flux (such as 

 that'from the sun) if the intervals in which one batch of cells completes its 

 dark reactions are used to expose to the same flax another batch, e. g., by 

 replacing the cells in the upper layer of an algal suspension with new ones 

 at a suitable rate. As part of the plans for large-scale growing of unicellu- 

 lar algae (for food, fodder or fuel), studies have been made of the possibility 

 of using a turbulent flow of algal suspensions to create such favorable mter- 

 mittencies of exposure; we will return to this topic on p. 1477. 



The relationships between the three above-used intermittency factors are 

 represented graphically in figure 34.5, which needs no further explanation. 



B. Flashing Light* 



1. Intermittency Factor in Flashing Light 

 Separate variation of dark and hght periods enables one to find out 

 more about the mechanism of the induction period and of the reactions 

 going on during the dark intervals than can be derived from experiments m 

 alternating hght with equal periods of darkness and light. We have en- 

 countered the first example of their usefulness in describing how Warburg 

 first determined the duration of the induction period and of the dark reac- 

 tion that prepares it. Emerson and Arnold (1932) made an important 

 contribution to the study of photosynthesis by introducing flashing hght, 

 meaning by this light with very short illumination periods, separated by 

 longer dark intervals. This method permits separation of the primary 

 photochemical process (together with such rapid nonphotochemical trans- 

 formations as are practically instantaneous, i. e., are completed withm 

 <10-3 second) from all those chemical or physical components of photo- 

 synthesis that require measurable time for completion. Two experi- 

 mental methods have been used to obtain the required intense light flashes: 



* Bibliography, page 1483. 



