Why club bouncers go around flashing lights in peoples eyes?

The club I went to this weekend is open really late ( until 7 am) on saturdays. Anyways it was around 3-4 am and we were still there. The security made it their job to go around flashing BRIGHT lights in peoples eyes (mostly the people sitting/standing around)...I personally think because around that time in a club ppl are on some type of drug to keep them going so security goes around trying to keep people from ping out? :S I don't know...it was just so unpleasant. Whats the real reason for why they do this?