The Talmud (Shabbat 86a) cites an opinion that prohibits relations altogether during the day. A compromise is made that relations are permitted in the daytime as long as the room is darkened. The halacha of a darkened room is applicable even at night.
Although there should be no direct light on you, indirect light, such as the light from the hall or bathroom, is permissible according to many authorities — as long as it does not actually light up the room and the light source is not directed on the couple.