just for grins if you are using 4.6V leds try hooking 3 of them up wihout a resistor and measure the through current when the supply voltage is between 12-15V. your brightness should be based on this current. You may find that you don't need to have a resistor at all (or possibly 10 ohm or...
The solution to this may be simpler than we are all thinking. some more information may be helpfull here in diagnosing a correct fix for your problem but i will throw out some ideas.
First off if your goal is to be as efficient as possible you may want to look the other way from where you...
