There are 2 fixtures hanging from each level of a 6' high x 4' wide foot wire rack for a total of 4 fixtures (8 bulbs). They are space 4" above a thermometer and they are hot....I can only touch the bulbs for 5 secs or less so I would estimate the temperature at the surface of the bulb to be around 130F+. I have the long sides of the rack covered with mylar to keep the light out of an ajoining room.

The room temperature is 66, near the rack is 77 and under the lights (4") the tempeature is close to 88.

Is anyone else seeing this? I have some T8 bulbs down int he basement (60F) and they are slightly warm to the touch.
If I need forced air cooling, I may go back to the standard T8 non-overdriven fixtures.

As for whether to stick with it, if you need more light and can't fit in more tubes then you'll have to overdrive. Or go to a different format like compact fluorescents or HID. But if you can fit more tubes in then you should probably do that. Overdriving uses more electricity, and produces more heat, than normal fluorescents producing the same amount of light, the only advantage is you need fewer tubes.

I got your email but you didn't show up in the members list at that time (a jedijfo did), so I couldn't send you an email here in The GardenWeb. However, I think it's better to answer here anyway, where answers are subject to "peer review" and suggestions by others.

I think the mylar sheets are the primary cause of your hot running. However, 130°F is about normal for an overdriven T8 at the surface. You drink coffee that is much hotter than that. And I seem to recall that a non-overdriven T8 is about 120°F on the surface.

As shrubs_n_bulbs suggested, you need some ventilation, particularly in the confined space between the mylar reflecting sheets. I use open chrome wire shelves and I use small electric fans to provide an artificial breeze for my seedlings.

If it's any consolation, your overdriving ballasts are actually running cooler because they are "loafing" driving a single tube instead of a pair.

You might want to re-think the placement of the mylar sheets. Perhaps if you described your layout in more detail, we could suggest a better alternative than your present setup.

MM

1.Reflect the light back onto the plants
2. Prevent the light from the shelves from blinding us in the family room next door.
The mylar only is on the long (4 foot sides). The bottom, top and sides of the rack are open.

With 2 normal fixtures I get a rise of only about 8-10 degrees. When the room temp is 60, the surface 4 in below is
about 68-70.. Seems alot better and I can touch the bulbs. Before the label on the reflector seems to be melting and caused a stink. I can always open the windows.. Plenty cold outside next to the rack...I hate to use more power. It is expensive here in the northeast

See my post here:

http://forums.gardenweb.com/forums/lights/?28645