Ballast Factor


IESNA Definition: the fractional flux of a fluorescent lamp operated on a ballast compared to the flux when operated on the standard (reference) ballast specified for rating lamp lumens.

Ballast factor (BF) is the measured ability of a particular ballast to produce light from the lamp(s) it powers. The ballast factor itself is derived by dividing the lumen output of a particular lamp-ballast combination by the lumen output of the same lamp(s) on a reference ballast. This factor, which usually results in a number less than one, accounts for the fact that some lumen loss results when operating lamps on commercially available ballasts.

Any single ballast may have several different ballast factors, depending upon the number and type of lamp(s) it operates.

If two 40-W fluorescent lamps rated at 3000 lumens each are operated on a two-lamp ballast, which has a ballast factor of 0.95, the actual lumens produced by the lamp-ballast combination will be:

3000 lumens x 2 lamps x 0.95 BF = 5700 lumens
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Glossary Terms: flux, IESNA