I have 2" dia. round dowel roosts and my hens always roost on them, my rooster that shares the coop with them roosts about half the time, the other half he lays on the floor right at the door. Go figure.
I have a pair that would always sleep on the 2 x 4 door brace, although they would sit on the roost some during the day. They finally figured it out on their own, and now sleep on the roost every night. To ZuniBee: How high are your roosts off the floor? I have 24 (a variety of breeds) and have 4 roosts staggered back and forth at different heights. They all get on the highest one about 20 inches from the roof. If yours were on the light, maybe they are looking for a higher perch.
Maybe that is what they are looking for. Mine are about 2 feet and then 4 feet. I'm going to be doing some work tomorrow so I'll try to build a higher one and see what they do.