Don't forget too that twighlight is their noon. We start to lose color as it gets darker, but most dogs have never had it, so they aren't disadvantaged by the darkness as much. If you can see shadows and stuff, chances are he sees more. I wouldn't worry too much. "Normal" households have too much light. If yours doesn't have enough, it'll probably have the same effect as too much light-- year-round shedding.
