Don't forget if you are temp testing with a bare tent it will read higher than what it would when there are plants/items in there to absorb some of that heat.
Also I run switchable ballasts (lumatek), bare in mind it pays to have the correct power bulbs for each setting. I'm no scientist but say you have a 600w switched down in power to 400 or below, although it will run the spectrums of light it puts out might be off.
Good luck anyway, Mitch
thanks for the info,i'll look into it