LED Flashlight

If you need to drive a number of white LEDs to provide display backlighting or for a white-light torch what’s the best way to configure them? If they are wired in series then the forward conduction voltage of the chain will be greater than the output from a typical battery. Connect them in parallel and current becomes a problem. To keep the light output constant it is also necessary to maintain a constant current through the LEDs despite a falling battery voltage.