PHYSICAL NATURE OF ANIMAL LIGHT 



59 



firefly.'' This is calculated to be .02 watts per candle. 

 More recent determinations (Coblentz, 1912), using a new 

 sensibility curve of Nutting's (1911) for a partially light- 

 adapted eye, give the reduced luminous efficiency as 87 



396^ 4-30.8 



A00_ \H 10 



TRAiyiVHOFER LINES. 

 6f6.3 687^ 7i6S 760. 



m 420 



-460 

 BLUE 



580 620 660 



YELLOW ORANGE 



700 

 RED 



7S0 

 INFRA-fl£0. 



WAVC-LENOTH, METERS . 10 



r» 



Fig, 15. — Spectral energy, luminosity and visibility ciirvea {after Gibson and McNicholaa) 



A. Spectral energy curve of Hefner lamp. 



B. Spectral energy curve of acetylene flame. 



C. Spectral energy curve of tungsten (gas-filled) glow lamp. 



D. Spectral energy curve of black body at 5000^ absolute (sunlight). 



E. Spectral energy curve of blue sky. 



Hg. Spectral energy curve of Herseus quarta mercury lamp. 

 Lt) Visibility curve for human eye. 

 Lo. Luminosity of Hefner lamp. 

 Le. Luminosity of blue sky. 



per cent, for PJiotinus pyralis, 80 per cent, for Pho- 

 tinus consanguineus and 92 per cent, for Photuris 

 pennsylvanica. 



The luminous efficiencies of various forms of artificial 

 illuminants have been calculated by Ives (1915) and are 

 given together with that of the firefly in Table 6. Fig. 15 



