Mine are 11 weeks and I still leave their light on all night (60 watt). They scream and cry when I turn it out, so I leave it on. I have to put it on in the evening to get them to go in. I'm thinking of putting a skylight in the roof to light up the coop in the morning and doing away with the night light. The windows are mostly blocked by fans, and it's quite dark in there. When I go in in the morning, they are all still asleep on the roost.
My older hens have no light in their coop, and never have had one. They know to go in when it's still light enough to see to get on the roost. There is one large window.