first of all the bulb that was in it had a VERY off center filimant., now that i finished my first mod in a 3d maglight, i have the bulb from the mag, its one of those bulbs that looks like a tube more than a "bulb" and almost like a magnified tip on it. anyway i put it in the dorcy 4 aa and it blew in like 10 seconds,so then i took one of the other bulbs i bought from radio shack for modding into leds and stuck it in the dorcy as well bright as hell, still going, dont know how long it will last the bilb is for a 2-3 d cell.