Today I picked up a 4' shoplight fixture from homedepot(canada).

Inside is a "CDL - M240120HR-01" magnetic balast intended for (2)F40t12 lamps. For an experiment I put my t8(32w) bulbs into the fixture with the magnetic balast. At 20" below the fixture I was getting just shy of 400 ft. candles. The magnetic balast was actually slightly(visually) brighter than my other fixture that I had already overdriven. It uses two Advance 2lamp F32t8 electronic balasts. I "overdrove" both bulbs. Under the light meter it read 290 ft.candles. This confused me. Then I thought that mabye it was possible that both balasts did not respond correctly. So on todays unit I used the 4-bulb electronic balast. I tried red-red / blue-blue, yellow on the ends... 290ft. Candles. Then I tried red-blue / red-blue, yellow on the end... again 290ft. candles.

Is there something about overdriving that I'm missing? these t8 bulbs are very bright... though why would they be brighter with the magnetic balast... when it's ment for t12s?

Is there something I'm doing wrong?