It depends. If you are using a philosophical lens, darkness cannot exist without light, nor can light exist without darkness. That whole Yin and Yang thing. Through a scientific lens, light is an energy called electromagnetic radiation and is mutually exclusive to darkness. Conversely, darkness is actually the opposite of brightness (not light) and it is a measurement of visible light. An object is understood to be dark because it absorbs photons, which makes it appear dim compared to other objects. In Destiny, I have no idea what the hell light and dark are because the story makes absolutely no sense at all.