I have a light that is only 950 lumen and it will blind anyone you light up with it.
I can shine the 950 on my hand for a few seconds and it gets pretty hot. The fact that it will temporarily blind someone makes it a defensive weapon.
I'd say you wouldn't need quite as much as 2700 lumen, about half that would probably work to blind an attacker in dim light. My 950 will make the room brighter even in the daytime, if your eyes are dilated at all it's def. going to blind you for a bit.
Something else you could use is a camera flash, if you can find one of the flash attachments that go on high end cameras, those will blind you in low light for sure, and they make a cool whining noise while they're recharging, would probably make an attacker think his ears are ringing and that you shot him between the eyes.
