what temp can 4 week old chicks handle

[mhbcbish]

I have 6 4 week old chicks, that are a hearty breed, I live in Michigan, the temp in my coop right now is 64 degrees, at 10:30 pm,going down to 54 degrees tonight, in a draft free coop, when can I turn off the red light at night permanently?

 

[Eggcessive]

I have a red GE 85 watt spotlight on my 3 week olds at night only when it is in the 40-50's. They seem to need a little bit just at night because day temps are 70's. Four week olds should need temps at 70-75F, but that is the hottest spot in the brooder. They will hang out in cooler areas. The 250 watt red lights are way too hot for them.