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Help To Determine Resistor To Dim Incandescent Light Bulbs

kapnKronik

Oct 26, 2017
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Oct 26, 2017
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Hi, I have recently installed new aftermarket gauges in my vehicle's dash, and they are too bright compared to my other older gauges. I would like to dim them to approximately 50% or 33% of their full brightness to match the others. I figured I could do this with a resistor in series for each bulb, but am unsure what resistor to use.

Each bulb is wired in parallel, 12V, and 3.4W each. They are incandescent bulbs. How would I go about calculating how much resistance needs to be added? What resistors could be used for 50% brightness, and for 33% brightness?

Or, is there a better method to dim these bulbs?

Any suggestions appreciated!
 

bertus

Moderator
Nov 8, 2019
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Hello,

A good way to dim lamps is PWM.
Have a look at this thead on All About Circuits:

Bertus
 

crutschow

May 7, 2021
861
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May 7, 2021
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It's difficult to know how much you need to reduce the bulb voltage to get the desired brightness.
A PWM circuit with a trimpot adjustable duty-cycle, such as bertus suggested, would allow you to easily adjust them to the desired intensity.
 

AnalogKid

Jun 10, 2015
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If you want to buy rather than build, my first stop is ebay.




ak
 
Last edited:

AnalogKid

Jun 10, 2015
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will those LED ones work on incandescent bulbs ?

Don't see why not. Two say LED because that's what most people are searching for. One says motor because that is another popular product. To be clear, I do not have any experience with any of these specific products. But a simple PWM circuit with a big enough power transistor should have no problem driving dashboard light bulbs of any flavor. I think they will work at least as well as the circuit suggestion.

At $1.65 (US), it is a cheap experiment.

ak
 

ivak245

Jun 11, 2021
113
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Jun 11, 2021
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113
The first one shown will work fine, and you can hook it up on the bench with a taillight globe or similar and try it out. Mount the whole board under the dash where you can still get the control knob.
 

Bluejets

Oct 5, 2014
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Or, is there a better method to dim these bulbs?
You might also consider an adjustable buck converter.(around [imath]3-[/imath]4.00 dollars)
Set output voltage to whatever brightness on the lamps and go from there.
One shown will handle 3A.

You said what the wattage of each lamp is BUT....not how MANY....:rolleyes:
 

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