Darkness

Darkness inhibits vision under normal circumstances. Areas of darkness are considered Heavily obscured, except that unlike most heavily obscured areas, natural darkness does not block vision of more distant illuminated areas. Magical darkness draws in light and prevents it from escaping -- it has all the properties of a heavily obscured area. 
Characters face darkness outdoors at night (even most moonlit nights), within the confines of an unlit dungeon or a subterranean vault, or in an area of magical darkness.