I just heard it's going to be in the twenties tonight and wonder if I should put a light in the tractor coop for my three 12 week old Orpingtons.
No extra heat should be necessary.
They've already grown their down feathers to keep warm.
You want them to naturally produce more down feathers or more fat to keep themselves warm according to whatever temp it is outside.
By providing supplemental heat, you defeat this purpose and they end up getting chilled.
Glad to hear it.