60 



THE NATURE OF ANIMAL LIGHT 



gives spectral energy curves for various illuminants re- 

 duced to 100 at A ^ .590/*, luminosity curves for the Hefner 

 lamp and blue sky, and a visibility curve worked out by 

 Coblentz and Emerson (1917) from observations on 

 130 individuals. 



Table 6 

 Luminous Efficiencies of Various Illuminants 



llluminant and commercial 

 description 



Commercial rating 



Lumens 

 per watt 



Efficiency 

 (visible radia- 

 tion X visual 

 sensibility -f- 

 total radiation) 



Carbon incandescent lamp 

 oval anchored (treated) 

 filament 



Tungsten incandescent 

 lamp, vacuum type 



Mazda, type c 



Carbon arc (open) 



Open arc, yellow flame, in- 

 clined trim 



Quartz mercury arc 



Glass mercury arc 



Nernst lamp 



Acetylene .' 



Petroleum lamp 



Open flame gas burner . . . . 



Incandescent gas lamp, 

 low pressure 



Incandescent gas lamp, 

 high pressure 



Firefly 



4 watts per mean horiz. c. 



1.25 watts per mean 



horiz. e. 

 600 C. P. 20 amp., 0.5 



w. p. c. Series type C. 

 9.6 amp. clear globe 

 10 amp. D. C. 



174-197 volt, 4.2 amp. 

 40-70 volt, 3.5 amp. 



1 L per hr. consumption 



Bray 6 high pressure 

 .350 lumens per B. T. U. 



per hr. 

 .578 lumens per B. T. U. 



per hr. 



2.6 



8.0 



19.6 



11.8 

 44.7 



42.0 

 23.0 

 4.8 

 .67 

 .26 

 .22 

 1.2 



2.0 



629.0 



0.0042 



.013 



.032 



.019 

 .072 



.068 



.037 



.0077 



.0011 



.0004 



.00036 



.0019 



.0032 



.96 



The firefly light by the above method of calculating 

 efficiency is not 100 per cent, efficient because its maxi- 

 mum (A. = 0.567/*) does not correspond with the maximum 

 sensibility of the eye (A = 0.565/i), but taking into con- 

 sideration also other effects of color, the firefly light would 

 be a still more inefficient and trying one for artificial illu- 

 mination, as all objects would appear a nearly uniform 



