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LED Flashlight

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Ok, I'm building an LED flashlight. It uses 12 high power LEDs, and what it all comes down to is that at 4.5V (3 "D" cells), I only need 5 Ohms of resistance. Now, a whole lot of energy goes into heating up that 5 Ohm resistor a whole lot. Is there a more effecient way? What I'd like is to be able to perhaps use PWM to short the battery out through the leds in quick bursts or something to that effect. I can use discreet components, but preferably stuff I could control from a uC. (Transistor, ADC for voltage/current sense built-in with the uC I'm using, a PIC16F876).


They want 30mA, but I'm considering either 25 or 20mA for better efficiency. (It doesn't look that much dimmer). The forward voltage is around 2V. I'm thinking of using a step-down regulator (97% efficiency, from National Semi) to give a PIC a constant 2.xV, and then drive the LEDs directly from the PIC by shorting the outputs to ground through the LED. The outputs on PICs can sink/source 25mA, so...

Is that idea any good?
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