Help To Determine Resistor To Dim Incandescent Light Bulbs

[kapnKronik]

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]

Hello,

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

Project: Simple PWM circuit

There have been a large number of requests for an easy-to-build PWM control circuit. You can always use a 555 or 556 timer circuit, but here's something you might build out of components from your "junk box." Attached is a schematic that uses a CMOS 4093 Schmitt input NAND gate in conjunction...

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Bertus

 

[crutschow]

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]

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

5A 90W PWM 12V DC Motor Speed Controller Module DC-DC 4.5V-35V Adjustable S D-FM | eBay

Find many great new & used options and get the best deals for 5A 90W PWM 12V DC Motor Speed Controller Module DC-DC 4.5V-35V Adjustable S D-FM at the best online prices at eBay! Free shipping for many products!

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Led manual dimmer / monochrome dimmer 12V 8A monochrome dimmer switch dimmFM | eBay

Find many great new & used options and get the best deals for Led manual dimmer / monochrome dimmer 12V 8A monochrome dimmer switch dimmFM at the best online prices at eBay! Free shipping for many products!

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12V 24V 30A LED Dimmer PWM Dimming Controller For LED Lights or LED Strip Lights | eBay

Input Current: 0-30A, Less than 30A.

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ak

 

[davenn]

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

will those LED ones work on incandescent bulbs ?

 

[AnalogKid]

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]

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]

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....