Im creating under-cabinet lighting, and my plan is to run a single Cree P4 on a dc power supply. heres the setup: radioshack dc power supply, set to 4.5 volts, 1 amp rated maximum, run thru 1 ohm 10 watt resistor and the led. im actually using 2 .5ohm 5 watt resistors in series. the led is mounted with thermal paste on a big heatsink.
i couldnt find a power supply with a voltage closer to 3.7v, so i had to work with what i had. Obviously 4.5v is too much for the led, without the resistor it drew 1.5 amps (too much for the led or the power supply). i added a .5ohm resistor and it went down to 1.2 amps. added another resistor (total of 1 ohm) and got 800ma to the led. perfect. at that power, it shouldnt get too too hot (especially with the heatsink) and the power supply is happy. and let me tell you my kitchen counter lighting is now beautiful (and efficient too)!
the QUESTION is: is this setup safe? according to my knowledge it is, tho my knowledge about these things is extremely limited (i read electronics for dummies). the power supple should have no trouble because it is rated for 1 amp (1000ma) and the led is drawing 800ma (measured with my multimeter in series). the led itself cant start a fire, can it? i cant think of any reason (after some testing) not to leave it on unsupervised. can you?
my kitchen counter has never looked better. the light is perfect for about 4 square feet but i think it would be better with 2 leds spaced out about 3.5 feet. i think to do this, i could wire 2 leds in series and use something like a 7.4v power supply (give or take a little and/or add a little resistance) that should give me around 800ma to each led (total of 1600ma so the power supply would have to have a high amp rating as well). makes sense right? any thoughts?