I use an Infrared on a timer to give my girls a bit of extra heat at night. All the info says they emit 'almost no visible light'. I've wondered about it, because I can certainly see by it well enough, but I thought, must be chickens see differently. This morning, however, I was awakened by the egg squawk at 4:23 - an hour before we turn on the lights. They were all awake and clucking when I went out there too, wanting to be let out to breakfast, so I'd guess they can see it all right. I will say they slept fine throughout the rest of night - the light was on at half hour intervals during the night and I didn't hear them until then.