From the photo, it appears your chicks could be between three and four weeks old. They seem to be well on their way to feathering out, therefore their heat needs are not nearly as critical as chicks in their first week, when all they have is thin down covering them.
Assuming all the chicks are around the same age, going by the fellow in the foreground, and he appears to be a cockerel, by the way, they may need little to no heat. A 100 watt bulb at night may be all they need, and temps of 75 F, 25 C, give or take depending on their development.
Why don't you take a little time and go fill out your profile so we know what region of the world you're from. It will help us all in advising you, knowing what your daytime and night time temps are. Your babies are close to being able to live outdoors in a coop.