Your Guide to Dimmable LEDs

Dimming LEDs is not as straightforward as dimming halogen or incandescent light bulbs. LED bulbs need a specific type of dimmer switch to work properly, and you need to be using specific dimming bulbs.

How do dimmers work?

Dimmer switches work by reducing the amount of voltage to a light bulb by rapidly switching the voltage to the bulb on and off, which results in a lower level of light output. There are two types of dimmers:

Leading edge dimmers

  • These are the original dimmer switches designed for use with incandescent and halogen bulbs.
  • They usually have a high minimum wattage load which means they are not suitable for LED or CFL bulbs. This is because even when the switch is set to dimmed, the voltage will still be enough to power LEDs and CFLs light bulbs fully & will most likely cause a buzzing sound as a result.
  • Leading edge dimmers work fine for halogen or incandescent bulbs as these bulbs have a much higher wattage than LEDs.

Trailing edge dimmers

  • These modern style dimmers offer a lower minimum load so are more suitable for use with LEDs and CFL bulbs. Trailing edge dimming provides a much smoother transition in light and is absent of any buzzing when dimming LED lighting making it the best option for most modern lighting circuits.
  • You can find out more about the science behind dimmer switches with this handy guide to How Dimmer Switches Work.

How can I find out what type of dimmer switch I already have?

Testing which type of dimmer you already have involves a bit of trial and error.

The best way to do it is to fit an LED bulb and see if the dimmer switch works with it. If it doesn’t, for example it may flicker or not dim at all, then it’s likely you have a trailing edge dimmer which will need upgrading.

When it comes to replacing the switch, it’s best to ask a qualified electrician to do this for you and you should expect to pay around £60 maximum for the switch to be replaced.

How do I know what bulb to use?

Not all LED bulbs are suitable for dimmer switches.

Packaging should clearly mark whether the bulb is dimmable or not. Look out for the following symbols:


If you’re buying your LEDs online then the product description should clearly state whether the bulb is dimmable or not. You can expect to pay £15 plus for a dimmable LED bulb.

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