Your friendly neighbourhood non-canon lore guy is here to save the day again! Light is many things. The energy emitted by light bulbs is light. But the light you speak of is an energy beyond our comprehension. It radiates from the Traveler, and each Ghost and Guardian has a small peace of the light in them. Light is the enemy of The Darkness, but The Darkness is not merely a lack of light. The Darkness is tangible. It has power. The Light and The Darkness have been locked in a war for untold ages. Light is the source of life, the source of hope. Human lifespans increased in the Golden Age not just because of medical advances, but also by having such a large source of light so near to them, in the form of the Traveler. The Darkness is the source of despair, of destruction. But it is not necessarily the source of death. Many aliens seem to thrive in the presence of the Darkness. And between The Light and The Darkness, in the place where the Awoken live, is The Grey. An absence of forces, yet a force of its own. The Grey is more mysterious than either the light or the darkness. Long ago, perhaps a millennia before the beginning of the Golden Age, The Grey surrounded the Earth. It gave birth to many mystical events, known at that time as 'magic'. Those who could wield the power of The Grey were known as 'mages' 'clerics' or 'fakirs'. But as the Traveler slowly grew closer to our solar system, The Grey was pushed away by the Traveler's light. Although this resulted in the disappearance of Magic, it also resulted in scientific advances, and the slow increase in lifespans of humans. In the end, no one can truly understand The Light. Still, guardians wield it, and use it as a weapon against The Darkness. -The Speaker, when asked by a young Guardian just what The Light was