How to DIM an LED Light?

Dimming an LED light is as easy as adding resistors to the connection or even several resistors, to ensure you get the right brightness – this is called analog dimming. In many states, there are regulations to the brightness (and colors) of LEDs on cars, which is why this is important to take note of.

You might not have as much control over the brightness as you would using pulse-width modulation (PWM). PWM means that you can encode how your LEDs will shine – brightness, color and characteristics – as well as have full control over the power supplied.

But, for the sake of convenience dimming an LED is just a matter of adding resistors, but this largely depends on how bright your LEDs are in their original state.


Forum Threads


ImagoX

Joined: Aug 24 2006
Posts: 2124
Location: Columbus, Ohio
Post Fri Dec 29, 2006 8:23 pm

One of the new LEDs I installed in my custom switchbox is… how do I say this?

It’s friggin’ brighter than the sun. icon_cool.gif

I noticed it right away the first time I fired it up at night and I thought I could deal with it, but man, it’s almost distracting.

Shy of tearing the wiring open to install a resistor (which would impede a portopn of the current and, I ASSUME, dim the LED), is there perhaps a way to cut the light instead? I was thinking of maybe grinding down the lens at the end of the LED – I figure of the tip is flat and diffuse that might be easier on the eyes while still being visable in the day….

What have you guys done to dim your LEDs? Or, are you all just bright freaks? icon_wink.gif

ImagoX

Joined: Aug 24 2006
Posts: 2124
Location: Columbus, Ohio
Post Fri Dec 29, 2006 8:25 pm

Oh, if I do end up just putting in a resistor, how would I calculate, say, dimming it by around 50%?
GlowinPontiac

Joined: Mar 04 2004
Posts: 5959
Location: Central CT
Post Fri Dec 29, 2006 8:54 pm

ive found that putting 2 resistors in series will significantly dim the led.

altho im sure there is a better way.

itzbjorn

Joined: Jul 21 2005
Posts: 2276
Location: MPLS Minnesota
Post Fri Dec 29, 2006 8:55 pm

This is a stab in the dark, I don’t know **** but I want to try and use my brain and see if I’m right.

You can DIM LED’s by giving them a lower voltage.

So, let’s just say, you run a 3volt LED at 1.5 volts, you’ve dimmed it 50%.

Find out what type of resister gets you from 12volts to the 3volts. Then find one to get you from 12vlts to 1.5volts.

Am I kind of in the right direction?

oldskoolhonda

Joined: Oct 16 2006
Posts: 1341
Location: Wichita, Kansas
Post Fri Dec 29, 2006 10:37 pm

i have mine hooked up to the interior dimmer control, works ok…wish it would go dimmer though
corvettecrazy

Joined: Dec 17 2003
Posts: 4357
Location: moved (twice)
Post Fri Dec 29, 2006 10:56 pm

itzbjorn wrote:
So, let’s just say, you run a 3volt LED at 1.5 volts, you’ve dimmed it 50%.

Yes reducing the voltage to the LED is a fine way to dim them. But you are wrong in saying that by cutting the voltage in half the brightness is also in half. They dont dim linearly like that.

You could also restrict current but I would suggest just adding a POT or another resistor in line (ground or positive) to reduce the brightness.

ImagoX

Joined: Aug 24 2006
Posts: 2124
Location: Columbus, Ohio
Post Fri Dec 29, 2006 11:15 pm

corvettecrazy wrote:
itzbjorn wrote:
So, let’s just say, you run a 3volt LED at 1.5 volts, you’ve dimmed it 50%.

Yes reducing the voltage to the LED is a fine way to dim them. But you are wrong in saying that by cutting the voltage in half the brightness is also in half. They dont dim linearly like that.

You could also restrict current but I would suggest just adding a POT or another resistor in line (ground or positive) to reduce the brightness.

Ah, that’s what I was wondering… so how DO they dim, anyway? Does anyone have experience with resistor dimming and can make a recommendation as to what I might try? I’ll be grindng down the LED tip in the morning and I’ll see if that spreads the light enough to make dimming unnecessary, but I’m thinking I;ll need to cut the light at least a bit in the end…

Thanks!

Dave

Joined: Aug 22 2006
Posts: 176
Location: CT
Post Sat Dec 30, 2006 12:44 am

Could always get some of that stuff they spray on to brakelight covers to get em darker.. Ghetto rigging’s always easier icon_surprised.gif
Ryan88

Joined: Aug 09 2004
Posts: 3516
Location: Pittsburgh, PA
Post Sat Dec 30, 2006 2:06 am

Buy some film and tint them!
Cyber Knight

Joined: Nov 23 2006
Posts: 523
Location: Calgary, Alberta
Post Thu Jan 04, 2007 10:04 am

I’d recommend picking up a couple of these little preset variable resistors (potentiometers) from an electronics store (radio shack or something). These are handy but be careful not to turn the resistance too low or you’ll let the smoke out of the LED icon_eek.gif . As long as it’s accessible you can keep adjusting it over the course of a few nights until you get it just right, and if you want to turn it up for oooo’s and aaaaah’s some night your have the power. Once you find the setting you like you can mesure the resistance with an ohm meter and then you’ll know what kind of simple resistor to buy if you want the same fixed resistance in the future. It’s nice to have a spare one of these for testing.
ImagoX

Joined: Aug 24 2006
Posts: 2124
Location: Columbus, Ohio
Post Thu Jan 04, 2007 10:11 am

That’s not a bad idea, actually… Any reason why I couldn’t just set it like I want and then leave the tiny pot in the switch box housing?

I ended up grinding down the tip and then used some transparent black INK (used for shading mminiatures) on it… Doing so had a dual benefit – it toned down the glare considerably and it also “stealthed” the LED – now it just looks like a round black nub until it’s lit up, which is pretty nice – un-inked the LED was white and very visable. I worry about pulling off the ink over time as I clean the box with a microfiber cloth, though, so a more permament solution would be better…

Thanks Cyber Knight!

Cyber Knight

Joined: Nov 23 2006
Posts: 523
Location: Calgary, Alberta
Post Thu Jan 04, 2007 10:56 am

ImagoX wrote:
That’s not a bad idea, actually… Any reason why I couldn’t just set it like I want and then leave the tiny pot in the switch box housing?

Thanks Cyber Knight!

No reason at all, that would work fine. And you’re welcome icon_smile.gif