The conventional Joule Thief usually using the 2N2222A NPN transistor which amplify current to power up LEDs ranging with minimum input voltage at 600 mV. However the brightness of the LEDs are not so significant compare to the high current transistor such as TIP41C as shown in this video. As you can see multiple arrays of LEDs bulb that requires at least 8 volt each can be light up simultaneously using 1.5 AA battery at once. This is provide more current then the smaller 2N2222A transistor.
Cheap Chinese made batteries has found its place in this circuit - and you don't need to buy expensive branded batteries anymore. And perhaps you can make your own batteries using aluminum + carbon and power up LEDs using this circuit. It gives an idea what we can do when we are living in remote area where electricity is not available - just with 1 piece of AA battery you can have a good lighting or probably making flashlight out of it.