Dimmer Switch Buzzing or Lights Humming: Causes and Fixes
Buzzing dimmers and humming bulbs usually come from a dimmer that is not matched to LED bulbs or is overloaded. How to fix the match, and when buzzing means a wiring problem.
- Difficulty
- Moderate
- Time
- 15–45 minutes
- Typical cost
- $0–$40 for compatible bulbs or an LED-rated dimmer
Dimmers work by rapidly switching power on and off many times per second, which reduces the energy reaching the bulb. That rapid switching can make the dimmer’s internal parts and the bulb’s filament or driver vibrate, which you hear as a hum or buzz. A faint sound is common; a loud one, or a sound that changes as you adjust brightness, usually has a specific cause you can fix.
What the sound is telling you
| Sound and situation | Likely cause |
|---|---|
| Buzz began after switching to LED bulbs | Dimmer designed for incandescent bulbs, not LED-compatible |
| Bulbs buzz or flicker at low settings only | Bulbs not dimmable, or dimmer’s minimum setting too low for LEDs |
| Dimmer buzzes and feels hot | Dimmer overloaded by total wattage |
| Buzzing with crackling, flicker or a burning smell | Loose connection or arcing: turn off the circuit |
| Incandescent bulbs hum on any dimmer | Filament vibration; rough-service or different bulbs may help |
Fix 1: Use dimmable bulbs
LED and CFL bulbs need to be labeled “dimmable” to work on a dimmer. Non-dimmable LEDs on a dimmer can buzz, flicker or fail early. Check the packaging or the bulb’s base. Using bulbs of the same brand and model on one dimmer also helps, since different LEDs respond differently.
Fix 2: Match the dimmer to LEDs
Older dimmers were designed for incandescent loads. Many LED bulbs draw so little power that these dimmers cannot control them smoothly, producing buzzing and flicker. A dimmer labeled for LED and CFL use, or “universal”, is designed for these low loads. Many LED-rated dimmers also have a small adjustment for the minimum brightness level, which can eliminate flicker at the low end; check the dimmer’s instructions.
Fix 3: Check the load rating
Every dimmer lists a maximum load, often separately for incandescent and LED bulbs. LED ratings are typically lower than the incandescent rating on the same dimmer. Add up the wattage of all the bulbs it controls. If the total is near or over the rating, the dimmer will run hot and may buzz. Replace it with a higher-rated model or reduce the number of bulbs on it.
A dimmer that feels slightly warm is normal. One that is too hot to keep your hand on is not.
Replacing a dimmer
- Turn off the breaker and confirm every wire in the box is dead with a non-contact voltage tester.
- Remove the cover plate and unscrew the dimmer. Photograph the connections.
- Most dimmers have wire leads rather than screws. Unscrew the wire connectors and separate the wires.
- Connect the new dimmer according to its instructions, matching ground to ground. For a three-way dimmer, identify the common wire before disconnecting.
- Twist connectors on firmly, tug each wire to confirm it is held, fold the wires in, mount the dimmer and restore power.
Some smart dimmers need a neutral wire in the box. Check before buying.
Worked example: adding up the load
Say a dining room dimmer controls a chandelier with six 9-watt LED bulbs. That is 54 watts of LED load. If the dimmer is rated for 150 watts of LED and CFL, it is well within range, and buzzing points to compatibility rather than overload. Now picture the same dimmer controlling three recessed fixtures plus a pendant, totaling 160 watts of LEDs. That exceeds the LED rating even though it is far below the dimmer’s 600-watt incandescent rating, and it explains a hot, buzzing switch.
When buzzing is a warning
The Electrical Safety Foundation International lists buzzing among signs that call for attention, alongside flickering lights, burning smells, discolored switches and warm outlets. ESFI explains that arc faults come from damaged, overheated or stressed wiring and devices. If a dimmer crackles, sparks, smells hot, or the cover plate is discolored, turn off the breaker and have the connections inspected before using it again.
Common mistakes
- Using non-dimmable bulbs on a dimmer.
- Ignoring the dimmer’s LED wattage rating and loading it with many fixtures.
- Mixing bulb types on one dimmer.
- Replacing a dimmer without checking for heat damage on the wires in the box.
When to call an electrician
Call a licensed electrician if buzzing continues after you have installed compatible bulbs and a correctly rated dimmer, if the dimmer or box is hot or discolored, if you hear crackling, or if lights flicker in other rooms as well. Persistent buzzing in the wall itself, rather than at the dimmer or bulb, can mean a loose connection somewhere along the circuit.