So in Lux's lore it says that she was able to easily replicate spells after having seen them cast only once. Both Morgana and Lux have very similar kits, similar enough that lux could have learned them from encountering Morgana.
Arclight Morgana and Ravenborn Lux Confirmed.
Light Binding, yes; the rest of her kit, not so much. I could swear it was canon that Lux modified the original spell after seeing Morgana cast it, but I can't find a source explicitly stating that. It is canon that Lux can reverse-engineer spells just by watching them be cast, so it's not exactly a grand leap to assume she stole Dark Binding.
