I ech WR Moore:

Depending on how you intend to use it, attaching a flashlight to an AR could be the worst thing you could do. Once you turn it on it may or many not illuminate the target, it can destroy your acquired night vision and as the only bright thing in the vicinity it can illuminate you as a target.

Get a sense for what it is going to be like by taking a cheap dollar store flashlight and tape it to your handguard with some electrical tape and practice with it; both leaving it on constantly and flashing it by manipulating the switch.

My bet is that if you do that, you'll decide you're better off without a light.