Light, except is physics, is a symbol.
The question is, what does the symbol mean? Most of the time, light is equated with "truth", which definition deserves it’s own discussion.
But its use goes back to the ancient world, long even before the Gnostics, the New Testament or Plato.
The ancient concept of it goes like this:
In darkness, one cannot see well. In light, everything is exposed. In darkness everything is hidden. In light, everything is open. Thus, light becomes a symbol for knowledge, for truth that was otherwise unknown and for personal openness.