BIOLOGY OF LIGHT PRODUCTION — MALUF 395 



article bearing the authorship of John Templer and the title, "Some 

 Observations Concerning Glow-worms." The note runs thus: "Mr. 

 T. also persuaded himself that he perceived a degree of heat from the 

 insect, when shining in its fullest splendour." In contrast to the 

 foregoing statement we have the following in a recent semipopular 

 article by Parlin (1935): "The ratio between the intensity of the light 

 [of a firefly] thus produced and the amount of matter oxidized is the 

 largest known to science, the efficiency being better than 95 percent! 

 Most of the energy in the latter case is radiated in the form of heat 

 . . . How the firefly can radiate 'cold light,' free from the enormous 

 amount of heat which is present in all man-made sources of light, is a 

 problem which has baffled science for many years, and its solution will 

 revolutionize our lighting industry." As will become apparent below, 

 both of the above viewpoints are unconscious exaggerations. 



The efficiency of a light source may be defined in three ways: (1) 

 The radiational efficiency, or the percentage of visible wave-lengths in 

 the total amount of radiation emitted, i.e., the amount of visible radi- 

 ation emitted divided by the total (heat, visible, and actinic) radiation ; 

 (2) the subjective radiational efficiency obtained by taking into account 

 the sensibility of the eye to different wave lengths, i. e. (visible radia- 

 tion X visual sensitivity) -*- total radiation; or (3) by the amount of 

 light produced in relation to a given expenditure of energy, i. e., the 

 total efficiency. Since the amount of heat evolved by a firefly during 

 luminescence, in excess of the basal metabolic level, or by an in vitro 

 luciferin-luciferase system has not been amenable to measurement 

 even by use of most refined technique (Langley and Very, 1890; 

 Langley, 1902; Coblentz, 1912) and since photography and other 

 methods have shown that apparently all the waves emitted are within 

 the visible region (see below), the radiational efficiency of biolumi- 

 nescence appears to be 100 percent. Harvey has pointed out, how- 

 ever, that it can be calculated that the amount of heat evolved from 

 the luciferin-luciferase concentrations so far used exceeds the limits 

 of error of available methods. At this point, Franklin's statement, 

 "being only discovered when separating," mentioned at the beginning 

 of this article, is symbolic. A work of great significance at this point 

 is that in which Harvey (1927a, 1935) showed that, for the production 

 of only one quantum of light of X=0.48/* in an in vitro system of 

 Cypridina luciferin-luciferase, about 100 molecules of oxygen must 

 react with the luciferin. The total efficiency of such a reaction would 

 thus be only about 1 percent, i. e., well below the total efficiency of a 

 number of man-made sources of light, including the incandescent ones 

 (see Hodgman, C. D. and N. A. Lange: Handbook of Chemistry and 

 Physics). The total efficiency of luminescences in general is not as 

 great as is commonly imagined. Thus, the efficiency of radiolumines- 

 cence (radium+ZnS) is about 1 percent (Hess, 1922); of phospho- 



