Is it possible to safely use a rheostat as a potentiometer to control an incandescent ceiling light? I have replaced a ceiling fan with a light fixture and would like to use the existing rheostat as a potentiometer.

  • The short answer to your question is: "It can't be done safely", but the longer answer is "It may be possible, depending on what's in the box." Can you post a photo of the speed controller, preferably showing its innards and wiring to the mains and to the fan?
    – EM Fields
    Oct 10, 2015 at 22:41

3 Answers 3


Come on guys the answer is absolutly not! the way both reostats and potentiometers work is they absorb the heat not used on the load so you would be making a wall heater in your box,,, a modern dimmer uses SCR or TRIAC solid state devices that limit the amount of AC making it to the load. Dont use a standard Dimmer for floresent lamps unless the ballest are listed for this. most dimmable Floresent lamps require a special ballest and dimmer combination. I thought I should specify, some old celing fans did use variable resistors to control the field winding (speed control) these can cause a fire if used as a dimmer, if the the device is a modern dimmer it would be ok to use it should have what it is made for listed on the body of the divice and how many watts it can handle.


This question is confusing. Rheostats and potentiometers are essentially the same thing. Modern household dimmer switches no longer use variable resistance; typically solid-state modulation is used to dim the light. If your switch is truly a potentiometer, I recommend replacing it with a modern dimmer which is vastly more efficient and safer.

  • 2
    Strictly, they're not the same since a rheostat is a two-terminal device and a potentiometer is a three-terminal device. Such being the case, a potentiometer can be used as a rheostat but a rheostat can't be used as a potentiometer
    – EM Fields
    Oct 10, 2015 at 22:23

Additional facts observed: I wired it up just to see the result. The two 60 W bulbs will only lite up (full bright) using the highest setting on the Rheo. No dimming apparent at 2 middle detentes. I will be swapping out the Rheo for a Pot. Thank you to all for responses.

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