The girls definitely aren't acting aggressive, or grumpy at any point during the day or evening. In the evening when they go to roost, they actually seem more friendly with each other. Girls who used to refuse to sit on the same roost together are now sitting side by side perfectly happy. It's hard to tell if the it has anything to do with the light, or if it's just that everyone is just so much more comfortable and at ease now that the big, bad guineas have moved. Our guineas used to chase/beat up the chickens fairly regularly. They've been gone a week now and everyone just seems so much more relaxed.
Our chicken house is designed with two wooden rods for roosting, one on either end of the house, one perch up above (our Leghorn used to refuse to roost near or below anyone else) and one nest loft. The Seabrights tend to prefer to sleep in the nest loft at night. There are 2 foot tall wire "windows" on all sides of the house, and we have a light-colored metal roof. This set up was great in the summer, very well ventilated and it even stayed quite "cool" (as cool as any building stays in NC in the summer!). I clean their house out regularly, but never noticed any odor. They're really only in the house during the night, the rest of the time they have a huge fenced area (probably close to 5,600 sq feet) to run around in and the ones who have figured out how to jump the gate are free to do so.
The red light doesn't seem to heat the house up too terribly warm, probably since the house isn't insulated, but definitely keeps it above freezing. The light is also far enough from anything that I don't think it should cause a problem. Of course, now I'm feeling a little paranoid and want to leave work to go check on them. The light's been up for over two weeks with no incident, but just when you think you're safe..... Great.
I tend to be a worrier, so I feel the areas all around the light on a regular basis (daily) to make sure nothing is getting too warm.
Anyway. Like I said before, I don't know that the cold was bothering the chickens. It was probably more me being bothered by the idea of something being out in the cold. If I had my way they'd come stay in the house with us on the particularly cold nights. Though I'm sure no one would like that, so it's a good thing my husband says no way to that one.