D&D 5E (2014) Using Darkness to cancel advantage and disadvantage.

[Sorcerers Apprentice]

Like many others I rule that you only get advantage for attacking when unseen if you can see the target yourself. Playing RAW in this kind of situation just results in too much weirdness.

 

[Asisreo]

I think an issue people have is that the strategy is purely metagame.

I can't imagine, say, a poisoned warrior's instinct to be to turn off the lights. But it's optimal from 5e's design, and not usually in any other game's design.

That being said, it's also a bit clever so I'm not opposed to allowing it.