Make sure the lamp is well secured. Dont trust the clamp it comes with,clamp it, tape it , screw it on whatever, but make sure it cant be knocked off. As the birds get older they will investigate it, jump and fly, play dive bomber with each other and it can get hit and knocked down.
My chicks were flying up and out of the tote I had them in by perhaps 3-4 weeks old. I used an old window screen on top to keep them in. This will give you a rough estimate of how big they'll be at 4 weeks.