simple question about dimming halogen bulb.

Thread Starter


Joined Aug 3, 2007
i have this bulb.

it is the 50 watt one.

Its awfully bright and would like to be able to dim it if i wanted to.

My friend told me to pick up a 5k ohm potentiometer and wire it up.

im wondering. can i use this potentiometer with Alternating current? will it work with this bulb?

i got it from radioshack. item # 271-1714

on the back it lists specs. i dont know what they mean

Resistance: 5k ohms +-20% tolerance
Rated Power: .5 watts
sliding noise: <47mV

any help would be great. and if you can suggest any thing else that would be better.. please speak up.


Joined Aug 3, 2007
Hi Tyler
Have you considered using a lower power rated bulb.

I don't think it's a good idea to dim a halogen bulb as it may not work correctly.

Generally the lower the power rating, the less light generated.

Heres a good link that may explain better than me.


Resistance: 5k ohms +-20% tolerance
Means the resistance value isn't exactly 5K.
The value can vary anywhere between 20% below or 20% above 5K .....
(4K to 6 K).

Rated Power: .5 watts
This is the power consumption the potentiometer uses in circuit.

sliding noise: <47mV
Less than 47mV of noise generated when the slider is move at say 20mm/s with say 20 Volts (or less if the rated voltage is less) across it.

Thread Starter


Joined Aug 3, 2007
thanks for that reply and link but.. what i really want to know is if that potentiometer above will work with 120v.. and will it actually dim the bulb successfully?


Joined Jan 10, 2006
You need a proper dimmer circuit using a triac. Just putting a Pot in series with the bulb will only succeed in burning up the pot.
Another consideration is that Halogen bulbs need to run at full brightness occasionally to stop the black discolouration you get in an underbright bulb.


Joined Jun 30, 2006
I'd recommend getting a lower wattage one.

You can dim halogen lamps but it requires some complex circuitry. A lab microscope light costs about $250.00 but does it well.

If I could see what it's mounted in you might be able to add a filter but that's difficult to do safely without taking a lot of hazards into account.