Well not everyone without a ready source of light. If it's magic of any kind, Vega can cancel it out with brute force.

But yeah that'd a problem. 

How about... It doesn't make them phase out completely? Meaning they'll be 50% solid, but it has the better application of being able to jump from shadow to shadow, sort of like from Aragami. You can be struck by most anything with 50% effectiveness and have high mobility in that form, although a clean hit will throw you out of it.