EFFICIENCY AND EFFICACY OF INCANDESCENT LAMPS

Planck's radiation formula is used to estimate the dimensionless effic iency of incandescent lamps as a function of filament temperature, wit h typical values of 2%-13%. Similarly, using the known spectral lumino us efficiency of the eye, the efficacy of incandescent light bulbs is estimated as a function of temperature, showing values of 8-24 L W-1 f or bulbs of 10-1000 W. The efficiency and efficacy results compare fav orably with published data and enable estimation of the filament tempe rature for any lamp of known efficacy. (C) 1996 American Association o f Physics Teachers.