I am starting my first LED project--I am wiring eight white LEDs for an ambient footwell lighting project in my 4Runner. Two per side under the front dash panel and two per side under the front seats pointed towards the rear footwells. I plan to use the standard 3.6V 20 mA white LEDs.

This would be one way to do it:


However, battery voltage (measured at the dome light, which will trigger the footwell lighting) can vary from 11.9 volts to 14.8 volts. Picking my resistor based on an average of 13 volts means I am pushing only 16 mA with the engine off and overdriving the LEDs at 26 mA with the vehicle running. If I recall correctly, LEDs are pretty dim at 16 mA.

Has anyone ever used a current-limiting regulator like the LM317? Supposedly all I need to balance the circuit correctly is R = 1.25 / I (I being the current in amps). So R = 1.25 / 0.020 amps (two 20 mA LEDs in series per array), which means a 62 ohm resistor and I'm set? This seems too easy. Anyone familiar with this stuff?