ok, it's a bit of an off-shot to use Warhammer 40k (and a parody vid on top of it) as comparison, but I feel the way bestboy Magnus explains the Chaos gods and their often forgotten positive aspects here is a good analogy of the light/darkness concepts. So far we thought that light was prosperity (Tzeentch) and darkness ruin (Nurgle), but it was actually the other way around:
Light is Nurgle - stability and order, but also stagnation and decay
Darkness is Tzeentch - any form of chance, from chaotic downfall to prosperity and hope

so as the WoL we tried to maintain order and prevent chaos on the source, and as the WoD we try to kickstart change and break stagnation on the first