Pretty simple build. And a good way to make a simple LED candle that uses 9Volt batteries. Actually this could be a nice build for halloween pumpkins now that I think of it. The LED’s used are 5mm ones from the looks of it. Pretty bright. Only thing that bothers me is there is no resistor in the circuit. Usually you need that to keep a battery like this from burning the LED’s out. Maybe they have it built in?
http://www.instructables.com/id/DIY-9-Volt-LED-EmergencyBackpack-Flash-Light/