"brad" writes:

Lew, can you give some rough idea of what kind of ballast losses can
be estimated? It probably depends on the quality of the ballast, but
is there a rough rule-of-thumb for typical medium quality-line Home
Depot fixtures?

You'll have to check a ballast catalog, but in days past, the input wattage
for a 2 lamp, 40W fixture was 92 watts.

It's not a big deal.

Lew