PAPERS OX CHEMISTRY AND PHYSICS 269 



If the radiations of an ordinary carbon or tungsten 

 filament could be converted into shorter wave lengths, 

 it would produce a light as efficient as the fire-fly and of a 

 more desirable quality. Electrical transformers are 

 used to step-up voltage; if there were a radiant energy 

 transformer to step-up vibration frequency, the infra- 

 red rays could be converted into visible light. The curves 

 illustrate the immense waste in producing light by pres- 

 ent methods. 



It is clear that for economic reasons research should 

 be directed toward finding a more efficient means of pro- 

 ducing light — that is, to reduce the amount of heat that 

 is generated when a body is caused to become luminous, 

 or to devise some method of producing light other than 

 by purely thermal emission. 



Electricity is by far the most convenient, safe, and 

 satisfactory means of producing light yet devised ; and it 

 seems likely that the solution of the problem of efficient 

 lighting, at least for a long time, will consist in some ap- 

 plication of the electric current. A comparison of the 

 relative efficiencies (or inefficiencies) of various means 

 of illumination shows that, although electrical means are 

 better than others, they are still extremely wasteful. 



In measuring quantity of light, as in the case of elec- 

 tricity, there is an intensity factor and a capacity factor 

 to consider, besides several other factors which deter- 

 mine the quality of the light. The unit of light intensity 

 is the candle-pouer, the unit of quantity or flow of light 

 is the lumen. In proper illumination a balance between 

 the two must be attained. Efficiency calculations based 

 upon the two factors separately and upon data from dif- 

 ferent sources agree only roughly, but all values point 

 to the same conclusion — that our best sources are very 

 poor when compared with ideal conversion of energy 

 into light. 



Coblentz 1 has determined the mechanical equivalent of 

 light and has shown that the theoretical conversion of 

 power into light of maximum visibility (yellow-green 

 light) is 617 lumens per watt. The conversion of solar 

 radiation is only 86.5 lumens per watt, so the sun, con- 

 sidered as a light producing source, is only 14 per cent 



