A simple (I hope) question arising out of my limited knowledge of ballasts in fluorescent light fixtures . . .

In determining the load that a fluorescent fixture contributes on a circuit, does the ballast figure in? That is, the load from 36 40W bulbs would just meet the safe "constant use" (80%) threshhold on a 15A circuit, but what about the ballasts in the fixtures? If ballasts make a contribution, where is the information to calculate it?