Yeah, it's probably Ether, but all I'm saying is that Ether might be Light-like. Ether Supplements for Light Substitutes is what I'm leaning toward now. I can't think of any other reason an advanced, sapient space-faring race would willfully submit to a substance to such an extent unless they 1) need it to maintain themselves, 2) they gain something incredible by using it. I imagine that The Fallen were once very different, and corporeal. They seem like the Light changed them - or at least a lot of them - and when they revolted or were broken by the Traveler, they needed something to replace the Light and developed their Ether.