I have a fluorescent light fixture in my bathroom ceiling mounted. It has two circular tubes, on is 32 watt and the other is a 40watt. About two years ago the 40 watt tube burned out and I replaced it. All was well. About a year ago the 40 watt burned out again. About 6 months later the 32 watt burned out. So I was going to replace both of them. I replaced them and when I flipped the switch they came on for about 30 seconds then went out, so I thought it was the ballast, so I called Lithonia an they told me to go to Home Depot and someone call them from Home Depot. So I did, the ballast came in and I picked it up had an electrician wire it in or what ever he did, later I got two new bulbs and it stayed on again about 30 seconds today and went out. The light fixture is about 3 years old. What else could it be?

The grounding of the fixture should be checked. Fluorescent fixtures must be grounded with a green or bare equipment grounding conductor to operate properly.

Fixtures that are not grounded or have a poor ground will work depending on the relative humidity, or not work at times.

Should be sure to match the lamps to the ballast. Should not be using 32 watt T8 lamps mixed with 40 watt T12 lamps.

Should be sure to match the lamps to the ballast. Should not be using 32 watt T8 lamps mixed with 40 watt T12 lamps.TK, I know you know this, but he has an old-school 32/40 circline fixture.
He is not mixing F40T12's with F32T8's.

Your right, I missed the word "circular".