Rodney,

As soon as my seedlings emerge, I remove the domes. High humidity and high temperature can make them spindly and susceptible to damping off.

Some seedlings can grow an inch overnight, so if you put the tubes an inch away you run the risk of the seedlings touching the bulb and being scorched. Two inches should be safe, but check them at least once a day.

I also have small fans creating a little breeze for them, which dries the surface of the medium a bit and "exercizes" the seedlings to make them stockier. Obviously the fans could not benefit the seedlings if the domes were still on.

For high light levels, I use six overdriven Philips cool white T8s per 18" x 48" shelf and eight overdriven Philips cool white T8s per 24" x 48" shelf. I get the T8 bulbs in boxes of 10 for $19.95 from Home Depot, so they cost $2 each.

MM

T12's, at least, don't get hot enough to burn seedlings (except at the ends) and can safely be put an inch from the foliage or even closer, though two inches is also fine. As maineman says, remove the domes as soon as the seeds sprout. It's also best to remove it for an hour each day while they are germinating to let the flats air out.