Whatever Bungie has listed as the recommended power. Don't listen to it, it's a lie lol you literally need to be 10-20 extra power level to even do the recommended power level quests or whatever. So if it says recommend power 580, and you are anywhere between 585-590. Guess what? Your still not strong enough to do it unfortunately lol. What it means is 580 = 600, unless your with a fire team that is at 600 light power and your 585 or whatever. Then your good to go. Or if your one hell of a OP player then your all good there to lol.