Ballast factor is the ratio of the light output of a lamp operated on a given ballast to its output on a standard reference ballast.
A ballast factor of 0.88 means the lamp delivers about 88 percent of its rated light. Fluorescent ballasts were commonly offered in low, normal and high ballast factors, roughly 0.7 to 1.2, which let designers trade light output against energy use with the same lamp. The term belongs to fluorescent and other discharge lighting; LED fixtures use drivers instead.
Why it still comes up
- Older garages and offices still have fluorescent fixtures, and their real output depends on the ballast installed.
- Comparing an existing system with an LED replacement requires knowing the actual output of the old one.
- Tube-style LED lamps may be designed to run on an existing ballast, bypass it, or both, which affects efficiency and maintenance.
In LED terms
- LED drivers are rated by output current and dimming range instead.
- Dimmable drivers allow light levels to be tuned and controlled. See adaptive lighting.
The Parkonomics view
Ballast factor is a legacy term, but it matters in every retrofit: you cannot measure savings or light levels against an old system you have not measured.
Related terms: Ballast, LED Lighting, Metal Halide Lighting, Lighting Power Density, Adaptive Lighting, Illuminance