'
When running on low the emitter still needs 3-3.5 V to operate? When dimming the light is it the current or voltage that's being lowered or both?
Both. LEDs have a nearly exponential current response when voltage is changed. So dropping by 0.1V might half current. Most white LEDs will glow, extremely dimly, on about 2.6v at less than 1 mA. This is a few mW of power. Also, most white LEDs have very unpredictable outputs in the hundred microamp range, and are not 'rated' for a certain output. Hook 2 "dead" alkaleaks up to a white LED in a very dark room to see this.
At very low drain, most batteries have higher available power than at higher drains. Alkaleaks have more apparent gain here because they suffer so much under high drain. Duracell alkaleak AAs, for example, are certified for power on an 8 ohm resistor. This leads to a 188mA 'drain test,' and gives about 1500-2000mAh available. At higher currents they may only have 200 mAh available, but at lower currents this can approach 3000 mAh. Sing it with me, Eneloops get 2000-2500 mAh, so the alkaleak just barely edges it out in very low-drain apps. Of course, it might leak during the month-long use, in which case you've gained nothing.
The driver in the Quark is a buck/boost driver. In boost mode it's probably 85% efficient, and in buck mode around 95% efficient. Since the LED takes "power" (Not amps OR volts, but BOTH), then we can calculate battery power, efficiency, and get LED power to estimate runtime. Say each eneloop is 1.2v@2000 mAh, each 14500 is 3.6v@750mAh, and we have a light that wants 3.2v@100mA. How long do we run on 1 or 2 eneloops, or 1 14500?
1 eneloop: 1.2v*2Ah = 2.4Wh. 85% efficient = 2.04 available watt-hours. The LED wants 320 mW, so expect to run for 6.3 hours.
2 eneloop: 2.4v*2Ah = 4.8Wh. 85% efficient = 4.08 available watt-hours. The LED wants 320 mW, so expect to run for 12.6 hours.
1 14500: 3.6v*.75Ah = 2.7 Wh. 95% efficient = 2.57 available watt-hours. The LED wants 320 mW, so expect to run for 8 hours.
These are only estimates, but show the idea.