Jacie, actually the temp range that is best is whatever makes them act like they are comfortable, milling around the brooder, eating and drinking, sleeping side by side, but not piled on top of each other like they are desperately cold. Observe them and they will tell you when they're comfy and warm enough.
I have a nursery coop that isn't drafty and I have a false ceiling that I can lower to make the 9 ft ceiling be a 5 ft ceiling over the babies' area. Then under that, I hang two heat lamps a couple of feet apart, in case one goes out at night, so they won't be left without heat. If it's in the 40's at night, I might put them out at three weeks old with a 250 watt and a 150 watt bulb (I have a great ultraviolet red reptile heat bulb a nice customer bought for me).
The pics I have in my purse are just a collage of pics of Suede and his ladies printed from my computer at home. I've posted them all here at one time or another. Had occasion to show a guy at the flea market who had chickens what a Blue Orpington was last weekend.