 The spectrum emitted by a blackbody radiator at temperatures of incandescent bulbs does not match the characteristics of the human eye, with most of the radiation in the range that the eye can't see.An upper limit for incandescent lamp luminous efficacy is around 52 lumens per watt, the theoretical value emitted by tungsten at its melting point.The spectrum of light produced by an incandescent lamp closely approximates that of a black body radiator at the same temperature.