ok, so i just pulled an led out of an old light up pen i had lying around and i want to know what it uses for power is there any way short of testing it to find out?
Those pens usually need one AAA battery to power the LED. Those batteries have the charge of 1.5V
Was there a little micro-circuit attached to it, or did the led itself unplug from the housing? Usually the wattage of the resistors used will give you a rough idea.