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The Problem with Dimmers

on February 4, 2016

Why isn't my dimmer switch working?
They help save money, reduce energy use, and give customizable light levels for any room in your home, but dimmers seem to be the finickiest and most failure prone control in the home.  How can something that is basically a glorified light switch be so difficult to install or upgrade without problems?  Don’t worry, there’s an answer to your problem, whether it’s buzzing wires, heated dimmer plates, or flickering lights.

How a Dimmer Works

Incandescent lamps work by running current through a filament that heats up and emits light.  The amount of light emitted is equivalent to how much power is flowing through the filament at the time.  Older dimmer switches took advantage of this using a variable resistor to adjust how much power the lamps received.

This outdated method of dimming lights runs into a couple of problems.  First, energy is still spent rather than being conserved. Second, variable resistor dimming does not work on CFL and LED light bulbs.  Newer dimmers use a method known as triac dimming, which uses an alternating current switch.  To save energy while still offering a smooth, adjustable-level of light, the dimmer cuts out a small portion of the electrical sine-wave.  As AC power moves from a positive value to a negative value (and back), a small portion is shut off, reducing the amount of usable power and dimming the circuit.

Even with a triac dimmer, not all LED and CFL bulbs are designed to work with dimmers.  If you want to dim the lights in the room you’ll need to make sure that:

  • All of the lights are the same type (LED, CFL, or incandescent)
  • The lights are compatible with dimmers
  • You have a compatible dimmer for the lamps

Compatibility needs to be on all sides of your circuit.  Otherwise you may end up with flickering, buzzing, or humming on your electric circuit.

Effective Dimmers

For your dimmer to be fully effective, it needs to be compatible with your lighting system.  But more than that, it needs to be capable of handling everything on the circuit.  You should never combine more than one type of light on the same dimming circuit because it adjusts how well the dimmer works (and may be the reason your lights are buzzing or humming).

Even worse, you should never overload your dimming circuit.  All switches, outlets, and dimmers have specific maximum wattage ratings on their construction.  They can only regulate so much power running through at once.  If you’re purchasing a new dimmer switch, consider how many lights, ceiling fans, or outlets will be on that single switch.  Most household switches are rated at 600 watts, with more durable switches reaching 800 or 1000 watts.

Ideally you never want to exceed more than 80% of a device’s maximum power rating.  If you know you’ll be overloading the switch, choose one with a higher power rating or use lower wattage bulbs.  If the faceplate on your dimmer is hot to the touch, you may be overloading it.  Try removing a few light bulbs and test to see if the faceplate still heats up.  If it does, reduce the wattage or upgrade your dimmer switch.


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