Dont put it on higher voltages, when manufacters sell their leds, they usually state like red leds are 2v - 2.6v, the first part (2v) is what you should run it on as its the voltage it is supposed to run on, any higher it uses more energy, much (at 2.6, MUCH MUCH) more heat, my blue leds at 3.6v (rated 3v to 3.6v) within a few seconds the hot glue around it would melt and in about 15 seconds the solder started to melt
I tried it with another led but instead at 3v, and it just always stays a bit warm and the difference in brightness isn't that much