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
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: