ashdec87

Hey,

I installed LED running lights the other day on my car. Works and looks great. They are wired to the parking light for power so during the day they can be run without the headlights, but at night they are a problem because they are SO bright. I could easily get ticketed or blind oncoming drivers with them. So to deal with this I would like to wire up the lights to a 3 way switch (mounted on the dash). One position will be 'dim' or 'night' and a normal on/off.

My question is, what's the best way to dim LED lights. I know hooking up resistors will dim it, but short of trial and error I'm not sure how to calculate the amount of resistors needed. The lamps draw 5 watts each, and I would like 50-75% brightness for the night. I'm thinking of adding enough resistors to cut the draw to 3-4 watts.. but I donno. I know LED brightness is not necessarily linear to voltage. Thoughts?

I'm also going to do the blinking sidemarker mod and eventually install a back up camera.

thanks

ash

Silva95teg

Cutting the voltage should cut the brightness, if you have access to diodes you could use a few in series. They will each drop about .7V You should use them if you want to run two power supplies to the string anyway to stop back feeding of voltage to your switch. Otherwise my guess is a 17 ohm resistor would drop about 6 volts, leaving you 8 v for the string. Thats calculated at 14v source for when the car is running. You would need at least a 2 Watt resistor. I am not 100 percent on my calculations, but thats my guess.

ashdec87

hm didnt really think about the voltage feeding back. Ok I can snag some diodes. I guess I can add them one at a time and see at what point they dim vs shutting off.. Might experiment with some LED's I have laying around before I try it on the car.

ashdec87

Does anyone know if this will work with on a cars electrical system since its only good to 12V?

http://www.superbrightleds.com/cgi-b...b-8a_specs.htm

would hate to burn it out because the cars voltage is a little more than 12..