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How to buy dimmable LED bulbs that won't hum, flicker or buzz

Not all LED bulbs are created equal. Here's how to be sure the ones you spend money on are dimmable.

LEDs that are incompatible with dimmers tend to flicker.

Colin West MacDonald/CNET

If you're shopping for LEDs, there are many options to choose from -- and dimmer compatibility only complicates matters.

Even if you pick the proper color temperature, lumens rating and a desired beam angle, you might run into another snag: dimmers. In many cases, your existing incandescent dimmers won't play nicely with newer LED bulbs. Unlike incandescents, all of which dim indiscriminately, LEDs either dim or they don't.

Hums, flickering and other dimming problems

With incandescent bulbs, dimming is simple, since the brightness of a the bulb is directly related to the voltage applied. Adjust the voltage applied by raising or lowering the dimmer and the brightness of the bulb will change accordingly.

The same isn't always true with LEDs, however. If you use an LED bulb with an incandescent dimmer switch, you may find that the bulb:

  • Doesn't turn on at all.
  • Only works at 100 percent brightness.
  • Turns on but hums or buzzes loudly.
  • Flickers at specific or all dimmer levels.

There is also a chance the LED works fine but shuts off or "drops out" below a certain brightness level. This happens when the applied voltage (or the average of the applied voltage) drops below the minimum voltage required to power the LED.

The sheer number of scenarios is due to LED bulbs having much more complex circuitry inside, referred to as the driver. This driver determines how the LED will react to different types of dimmers: incandescent phase control, leading-edge, trailing-edge, three-wire Lutron, or 0 to 10V dimmers.

And just because one LED dims just fine with one type of dimmer, that doesn't ensure it will work with others.

Why aren't some LEDs dimmable?

But why are some LEDs not dimmable at all? Simple. The manufacturer decided to leave out the feature: it simply was not included in the circuitry. Often, this means cost savings for consumers who don't need dimming capabilities.

Tips for buying dimmable LED bulbs

  • LEDs that are dimmable are typically labeled as such on the box. If it isn't labeled as dimmable, it's safe to assume it isn't.
  • While some LEDs work just fine with traditional incandescent dimmers, it's suggested that when you upgrade to LEDs, you should also upgrade to LED-specific dimmers.
  • While a non-dimmable LED may perform well in a circuit with a dimmer switch (incandescent or LED) set to 100 percent, there is a chance the light will flicker and hum at other brightness levels. Also, it may dramatically shorten the life of the bulb.
  • Smart bulbs are not meant to work with dimmer switches of any type. They have a built-in dimming mechanism that will conflict with a wall-mounted dimmer and cause the bulb to flicker, hum or simply not turn on. It's best to use the app or included remote to dim them instead.