I am currently propagating various shrub cuttings using a 7" humidity dome over a single flat. I have a 2-foot, 4-bulb t5HO fixture (96 total watts from the bulbs) hanging about 6" above the top of the dome. Unfortunately, temperatures inside the dome are sitting around 89-90 degrees F.

So:

1. This temperature is too high, right? Soil temperature is supposed to lag air temperature by about 10 degrees F (is this still true in an enclosed area such as a flat covered by a dome?), which means that I should be looking at soil temperatures around 79-80 degrees F. This is a bit too high.

2. The ambient temperature in the room is 75 degrees F. So the light is heating up the enclosed dome by a good 15 degrees F. How can I mitigate this? I know cuttings don't need excessively high light levels, but there is a fair amount of light loss through the plastic of the dome. Raising the light higher could reduce temperatures inside the dome, but I would lose light intensity.