Lighting, Light Fixtures, Ceiling and Exhaust Fans - Help- fluorescent fixture needs a whack to light!

We have a fluorescent fixture in our garage that just started acting funny. It used to light up almost instantly when throwing the switch. Recently, when the switch is thrown, the bulbs (two ~47") glow very dimly, with lot's of dark rings that seem to dance around inside the bulbs. If I give the fixture a whack with my hand, both bulbs instantly pop on to a normal bright constant illumination. If I switch the fixture off and back on, same problem. They won't fully illuminate without a good slap.

The ambient temperature in the garage is 60-65 F, and the fixture is a "rapid" type.

Should I just try new bulbs first, or is this a common sign of something else?

I always try new bulbs first. It's cheap and easy.

If the new tubes work but you notice the problem returns in a month or two, or if you notice the ends of the bulbs turning dark after a few months then the ballast is probably is dying.

If the new bulbs don't help then it's new ballast time.

Thanks- new bulbs seemed to do the trick... I can't beleive I was that ignorant!