Eh, I've been a fan of making up my own story for it, and seeing how long it takes before people realize it's not the "official canonical" version.
My highly strange improbably fantasy is that the Light was a conceptual power given more form than usual by the complex interaction between the power supplied by collective human consciousness focused in the transient world via the catalyst of faith, and the ambient dissociated "particles" of concepts floating about due to the interactions of the "darkness" extreme, aka the Invaders.
So in other words, the power of faith, given form, an opposite to that which gave origin to the triple divergent or perhaps convergent branches of darkness.
