i'm no expert but i've always thought yellowing in any plant leaf is often a sign of a lack of iron? especially if the veins/strands/thingy bits that hold the leaf together stay darker than the actual leaf if that makes sense?
it could be another deficiency though. zinc, manganese, or even nitrogen.
buuut the fact that the thing you changed before the yellowing was the light, then it's probably the lighting change?