Fluorescent fixture not working right

The fluorescent fixture (2 42" bulbs) has begun to light at about 205 of normal brightness (maybe less- it’s hard to estimate). Is ther any easy way to tell if the problem is bulbs or ballast?

Sorry, that should’ve said 20%, not 205.

Yeesh. Wrong forum. Mods, please delete this thread - I’ll repost in GQ.