I have a 100 watt in my coop, along with a 40 watt green bulb (mostly for Christmas)... my lights go off around 10 pm. It gives them a little heat (very little)... but they seem to like being in the coop in the evenings and having a light on. I sit in my dining room and watch them through their windows... I see them preen themselves, fuss with their feathers, interact with each other, snack, actually it is pretty cool watching their behavior. They know just about when the light is going to go off as they all seem to head for their perches and the Silkies head for the nest box... they are tucked in and ready within 5 minutes of the lights kicking off. Up until then, they are very busy, like a bunch of women hanging together quilting or something. I really enjoy watching them.
Diana