That I have no idea, you need a flashlight where you can store batteries that give you a total of 6v or more since you need a minimum of 5.25v to drive a red diode with rkcstr's driver, you could get a flashlight that uses 2 CR123 batteries, or two AA batteries, you could buy two 14500 lithium 3.6v rechargeable batteries that you could put in the AA flashlight to give you a total of 7.2v. It's your choice, what kind of batteries are you planning on using?