Trailing Edge Dimmer vs Leading Edge

If you’re looking to buy dimmer switches, you’ll no doubt have seen trailing edge and leading edge dimmers for sale on various websites. One of the most popular dimmers is a intelligent trailing edge dimmer switch from both Soho Lighting and Lieber Lighting, so in this article by our in-house Electrician/Technician, we look at the differences between leading edge and trailing edge dimmers so you can choose the right type for your needs.

What are leading edge & trailing edge dimmers suitable for?

Leading edge dimmers are suitable for inductive load, for example magnetic low voltage transformers; and resistive loads like incandescent light bulbs. They are generally unsuitable for LED light bulbs.
Trailing edge dimmers are suitable for capacitive loads like electric low voltage transformers and LED drivers as well as resistive loads like incandescent bulbs.

Simply put, leading edge dimmers tend to be unsuitable for LED bulbs, so if you’re looking to switch to LED, and you use a dimmer, you’ll need to switch to a trailing edge dimmer too.

Why choose intelligent trailing edge dimmers?

These are a great long term purchase, as they are suitable for all types of lighting, unlike leading edge dimmers. The benefit of choosing an intelligent trailing edge dimmer is that they recognise the load and self adjust when switched on. They also have adjustable parameters for minimum load.

One problem with leading edge dimmer technology as they don’t work with all types of bulbs, but the universal usability of intelligent trailing edge means that you don’t have to check whether you have the correct switch for the bulbs.

The soft start technology in the dimmer switches also helps get the most usage out of your LED bulbs too, as it means less ware is put on the LED chips so the bulb / light source should last longer.


Trailing edge dimmers, being more sophisticated than leading edge dimmers provide a much smoother dimming control, meaning you won’t hear buzzing.

Whilst leading edge dimmer switchers are often cheaper and simpler than trailing edge, they were originally used to dim halogen and incandescent bulbs or wirewound magnetic transformers. They tend to have a relatively high minimum load, which makes them unsuitable for LED or CFL lights. Leading edge dimmers are still very common, but as more households switch to LED, more are switching to trailing edge.

How do trailing edge dimmers work?

Trailing edge dimmers work by cutting the second half of each half cycle in an AC wave.

Why do lights buzz when dimmed?

This was a common issue with the old style leading edge dimmers and dimming either incandescent or halogen bulbs. The noise you hear is the hyper-fast AC interruptions that change the level of lighting.

Should dimmers buzz?

Dimmers will generally buzz due to it being an old style leading dimmer which is close to its maximum loading capacity.

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