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White leds are current mode devices, so to drive it properly you need a constant current source not a constant voltage source. Ideally you want a current mode boost converter otherwise you won't get the best out of the led. Laser diodes are also current mode devices ;) An LM317 can be used as a very basic current source but won't boost the voltage only drop it. All these 10w less are slightly different so some will draw 10v whilst others 12v. Hope that helps clear things up for those that don't know.