Dimmer Switches work by reducing the power delivered to your light bulb.

They do this by trimming a section of a waveform, either on the leading edge or trailing edge of the wave.



View our entire range of dimmers here.



Manufacturers have designed their LED light bulbs to be compatible with the majority of common ‘trailing edge’ household dimmers. Trailing edge dimmers are slightly more complicated and more expensive than the ‘leading-edge’ versions but they have many more desirable features such as smooth control, silent running, soft start and multi-way dimming that greatly enhance the life of the LED light bulbs. For a more comprehensive rundown of dimming and dimmer switches in general, check out our Dimming for Dummies guide.


How Do Trailing-Edge And Leading Edge Dimmers Work?

Trailing-Edge

trailingedgewaveform.jpg
Trailing edge dimmers are designed to fade the voltage to zero rather than switch it abruptly off, by applying resistance to create a ramp. This increases the amount of heat dissipated since the resistive period generates heat.


Leading Edge

leadingedgewaveform.jpg
Predominantly used with incandescent or mains halogen light bulbs, leading-edge dimmers are compatible with resistive or inductive loads and can reduce the load by shortening the cycle at the leading edge of the input waveform.


How Many Light Bulbs Can Be Used With A Dimmer?

All dimmer switches have a minimum and maximum rating (Watts). Unfortunately LED loading cannot be calculated the same way as a traditional incandescent or a mains halogen light bulb. A good rule of thumb to apply – one that is used by most manufacturers – is to take the maximum rating of the dimmer switch and divide by 10 (or in other words use 10% of the max. rating). As an example – if you have a dimmer switch with a maximum rating of 400W (rule of thumb translates to 40W) you can run five 7.1W dimmable LED light bulbs (see example below for further explanation).
LED Dimmer Loading

It is worth mentioning at this point that all manufacturers state that their LED light bulbs are designed to be compatible with the majority of common household dimmer switches but they cannot 100% guarantee that they work with them all as there are so many makes and models on the market today.

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[…] Okay, so there are numerous types of dimmer switch available, but by far the most popular are the two that we’ll be concentrating on today – leading edge and trailing edge phase-cut dimmers. […]

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[…] surprise you that the development of LED lighting has complicated this too (luckily, we also have a guide to help with […]

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[…] For further information read our guide on dimming LED lamps. […]

Aurelian Georgescu
Aurelian Georgescu
May 4, 2020 10:26 am

I have 29 GU10 LED SMD with 7W , which dimmer switch I need to use , Thank you

kelly Morris
kelly Morris
May 23, 2020 1:57 am

I have a much smaller situation. I’m just connecting under counter lighting in a kitchen using Kichler LED lights, and the lights flicker when we dim them. The whole house has push button switches which is also challenging to find what will work with the LED fixtures. I’m afraid that I need to find a lighting engineer. Please help!

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[…] Determining how many light bulbs you can use with one dimmer switch takes a little calculation. You can learn more here. […]

Alexander Morrison
Alexander Morrison
July 31, 2020 7:46 am

l have 7x 50watt halogen street lamps and want to dim them, any suggestions?

Philip Whitehill
Philip Whitehill
August 8, 2020 3:01 pm

I’ve just bought a Celling light . And the led driver says 40-60w . Ac165-265v . 50/60/hz can you get me a switch please for it

Randy
Randy
September 25, 2020 11:47 pm

Hi Matt: In using a universal slide dimmer switch the manufacturer list the maximum rating Watts as follows: for dimmable LED/CFL 150-Watts; for Incandescent/Halogen 600-Watts. Would you still require the 10% rule in calculating the number of dimmable LED light bulbs given the manufacture makes the distinction between the maximum wattage for the different types of bulbs? If you use the dimmers LED maximum watts as 150W, then the following would be true: I have a light fixture requiring 6 bulbs. The dimmable LED bulbs are 7.1W per bulb. Therefore 6 LED dimmable light bulbs X 7.1W each = 42.6… Read more »