My suggestion is not to go by a thermometer reading, but by their behavior only. First have the heat light only on one side of the brooder and nothing on the other side. Watch them where they lay down. Do they move under the light or do they move away. Under means they need the heat, huddling under the light means increase the heat, and away means reduce the heat. I tend to only use regular white light bulbs. The red heat lamps are way to hot. I start off with 90 watts from 2 feet above. Then I reduce to 75, 60, 40 watts. After that they don't need it at all. You may need to only give a little bit of heat at night, depending on their brooder's location. I keep mine in the kitchen without much temperature fluctuations between day and night so I never have to worry about the night. Now with being summer you may get them weened of heat really fast. Mine were done at 2.5 weeks in the house, but I did supplement the heat at night when I moved them to the duck house. Temps were falling into the 50s inside of the duck house without heat. I basically put in an oil filled heater and but it on low. They snug up to it as needed, which was very little at all. They preferred the concrete mixing bins full of pine shavings where they pilled up into it. I guess they liked the nest and cuddle idea more.