I have 1 month old chicks (4 to 4 1/2 weeks old) outside in an empty coop. I have put a heat lamp in the coop the last 2 nights because the lows are in the upper 20's. I've never seen them huddling under the lamp when I check on them. Should I switch to a regular light-bulb? I don't want to get them too dependent on the heat lamp but also don't want to have them freeze. Oh and after tomorrow night Lows will be in the 30s/40s and highs in the 40s/50s.