Luminous Efficiency

In this paper are outlined the scientific methods which have been employed at one time and another in comparing the efficiencies of light sources. The methods of estimating and the values obtained for "luminous efficiency" and for the "mechanical equivalent of light" are noted as briefly as possible, chiefly for the purpose of showing in what way they are inadequate for out present more exact needs, and in how far they have assisted toward the more satisfactory idea of efficiency now possible The writing and experimental work of several men are drawn upon freely, in particular the excellent discussion of Drysdale. The object here is not so much to present original work, of which there is very little, as to aid in clearing up the confusion which exists at present, and to bring to the solution of the scientific side of the problem some pieces of work which have only recently become available, or whose availability has not heretofore been realized.

The discussion center about four topics: (1) "Radiant Luminous Efficiency," the most frequently used basis in comparison of light sources; (2) "Total Luminous Efficiency"; (3) "The Mechanical Equivalent of Light"; and (4) "Reduced Luminous Efficiency," the term applied to Drysdale to the more rational and exact basis of comparison which it is the object of this paper to present and emphasize.