With my chicks, I used a reptile lamp due to the size of the brooder and the hatch size (2). I didn't want it over heating. But, the temps were never at the 90° mark or anywhere near it. I wasn't planning on brooding any inside, I was going to go the "wool hen" route with the temps and number that was supposed to hatch. But since I only got 2 out of the handful of eggs that I was given, I felt better letting them brood under a lamp with some heat. My example is nowhere near the capacity that some of you have had. But, with the chicks, my reptile heat lamp never got above 75° and that was directly under the lamp.
The outdoor temps at that time were in the 80s and 90s. So during the day, I had them outside in the run with the other chickens bit in their own area. I set up a "cave" with fleece (like the wool hen idea). I would put them back in the brooder in the late afternoon. They had a piece of fleece and they loved sleeping on that. They never seemed chilled and mine never got pasty butt.
I have also had a brood of week old ducklings. The way I set up the heat lamp, it was too far away to give a direct 90° under the heat lamp. When I measured where their bodies would be, it was more like 78°. But, I was afraid to have the lamp any closer for fear that the lamp wouldn't be secure enough and cause a fire. That would not have bode well with the husband if I burnt down his work shop.

With the ducklings they had a large kiddie pool and definitely had places to get warmer if needed.
I was so worried at first in both instances, but after reading great articles here as well as online research, my worries were relieved and I just let them be. I even read where some brooded in their house with just warm jars of water - no lamp, no electricity. I think most first timers are worried, but given the idea that nature is not as strict as humans are helps to alleviate the stress of brooding. The best tool to use when rearing animals is the tool of observation. When you observe that something is or is not working, then you can tweak it and go from there.
