Lumens Per Watt. A measure of the efficiency of a light source, equal to the lumens produced, divided by the power (watts). For example, a 100-watt lamp producing 1750 lumens yields 17.5 lumens per watt.
Lumens Per Watt. A measure of the efficacy of a light source in terms of the light produced for the power consumed. For example, a 100-watt lamp producing 1750 lumens gives 17.5 lumens per watt. Examples: Edison's first lamp 1.4 lpw Incandescent lamps 10 - 40 lpw Fluorescent lamps 35 - 100 lpw Halogen lamps 20 - 45 lpw Mercury lamps 50 - 60 lpw Metal halide lamps 80 - 125 lpw High-pressure sodium lamps 100 - 140 lpw