Good grief. Chicks at four weeks do NOT need a heat lamp! Do. Not. Need. Heat. Unless it's below freezing. Do you keep your house at 30F?
Your chicks need space. They need a coop. They need a run to run around in.
How is your weather these days? Is it getting into the 70s during the day? Is it above freezing at night? If so, you can begin letting your chicks spend all day out in the run and bring them inside at night. After a few days of that routine, you can move them into the coop and let them fend for themselves.
No heat unless you want to keep them from ever being cold hardy.