It's outer space, so I guess it's constantly night.
Or one might consider it constantly daylight.
Vampires are said to be burned by daylight, yet the Moon can reflect enough sunlight to cast shadows at night. Why doesn't that hurt vampires? "It's a matter of intensity," one might say. Then we see scenes like Will Smith being terrorized by vampires in I AM LEGEND. It is close to sunset, and only a tiny sliver of sunlight passing between some buildings holds the demons at bay. Fire will burn people, but one can pass a hand quickly through a flame with no more damage than some singed hairs. Why couldn't the demons leap through that tiny sliver of light? And what about the light from the sky overhead?