I'm curious, what does the ballast do? I see it referred to on light
fixtures I've installed, but I've never quite figured out what it is.

bob
k5qwg


The ballast serves two purposes -
it 'strikes the arc' (starts the current flow)
and it
Limits the current flow
(otherwise current would spike and destroy the fluorescent lamp)

The efficiency of a fluorescent fixture is dependent partly on the ballast -
and usually - electronic ballasts are the more efficient of the two. HPF
ballasts usually use less current than a standard ballast.
You Compare fixture efficiency by comparing the ballast specifications
assuming they use the same lamp.
The web site that John Smith posted a link to explains it pretty well.