A long hall or a room with two doors often has a light switch at only one entrance. Adding a switch at the other side typically requires running a new cable between the two switch boxes and replacing the single switch with a pair of three-way switches. Conversely, a standard replacement switch or a new dimmer simply installs directly into the existing box.
Nearly every bulb sold today is an LED, and these do not always perform well with dimmers designed for incandescent bulbs. They can flicker, buzz, or fail to dim smoothly. Consequently, a new dimmer must be explicitly rated for LED loads and paired with bulbs that are labeled as dimmable.
What This Covers
- Replacing worn, loose, crackling or hot switches
- Single-pole switches
- Three-way switches for control from two places
- Four-way switches for three or more places
- A second switch location for an existing light
- LED-compatible dimmers, including three-way dimmers
- Fixing miswired three-way switches
Signs It’s Time to Call
- A switch crackles, pops or sparks when you use it
- A switch plate is hot, or a plain switch feels warm
- The toggle feels loose, or the light only works if you hold it a certain way
- LED lights flicker, buzz or won't dim smoothly
- A stair, hall or large room has a switch at only one end
- Three-way switches only work in certain combinations
The Process
See How the Light Is Wired
We turn off the breaker and open the switch box to inspect the wiring configuration, verify the presence of a ground, and identify the type of wire. If aluminum wiring is found, it requires a switch specifically rated for it.
Match the Device to the Load
The switch or dimmer is selected based on the specific load it controls: the type and total wattage of the light bulbs, whether a fan is on the circuit, and the number of locations controlling the fixture.
Mount the Switch
A standard replacement fits directly into the existing box. However, a brand-new switch location requires routing a new cable between the boxes, typically fished through an attic or crawl space.
Set the Low End
Every switch position is tested, and dimmers are operated across their entire spectrum using the exact bulbs you intend to keep in the fixtures. If the dimmer features a low-end trim adjustment, it is calibrated to ensure the lights do not flicker or cut out at their lowest brightness level.
Common Questions
Why do lights flicker or buzz on a dimmer after a change to LED bulbs?
This typically occurs because the dimmer and the bulbs are incompatible. Older dimmers were engineered for incandescent bulbs, whereas LEDs rely on internal electronics that react to subtle electrical fluctuations that a traditional glowing filament simply ignores.
Dimmer manufacturers publish compatibility lists detailing the specific bulbs they have tested with each dimmer, which should be verified before purchasing either component. Because buzzing is heavily influenced by the bulb's internal design, switching to a different brand or model can often resolve the issue. If the lights flicker on a standard switch as well, or if the flickering occurs throughout the entire house, it indicates a separate underlying issue that should be inspected immediately.
What's the difference between three-way and four-way switches?
A three-way switch operates as one of a pair that regulates a light from two separate locations. Neither switch has a fixed on or off position, as flipping either one simply reverses the current state set by the other. To add a third control point, a four-way switch is installed between the two three-way switches, and every additional control location requires another four-way switch.
The electrical code mandates a light switch at each floor level for any stairway containing six or more steps between stories.
Can any light go on a dimmer?
Most can, provided you use the correct dimmer. The bulbs or the light fixture itself must be labeled as dimmable, and the dimmer switch must be compatible with that specific type and size of electrical load, though certain fixtures cannot be dimmed under any circumstances. Additionally, two things should never be connected to a standard light dimmer: an electrical outlet and a ceiling fan motor. A dimmer can easily damage a fan motor, which requires a specialized speed control designed specifically for that purpose.
It is completely normal for a dimmer to feel slightly warm during operation, as it naturally dissipates a small amount of heat. However, a dimmer that feels hot to the touch, shows discoloration, or emits a burning plastic odor is faulty; you should safely turn off its circuit breaker at the panel and have it inspected immediately.