Set up your brooder with the thermometer under the light, and check ground level temps at various distances from under the light. With a brand new set-up, you need to get baseline data. It depends on ambient temp. too. I know how my brooders work so don't use a thermometer any more. Get organized before the chicks arrive, then watch their behavior; the babies will let you know how they are doing! Most important, double or triple attach your heat lamp to prevent fires, dead chicks, and the loss of your building! Mary