What Makes An “LED Compatible” Dimmer Switch?

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Firstly, you need to make sure your led dimmer switch operates on either leading edge (MLV) or trailing edge (ELV) technology. If you’ve got an old inductive dimmer switch it’s never going to work with LED lights. These two slightly different styles of dimming are known as TRIAC or mains dimming.

They dim the lighting by cutting off the RMS (root mean square) voltage to the lights. When the lights are being dimmed, the voltage gets cut off so fast that the lights are flickering, but too fast for the human eye to see.

How ‘Leading Edge’ Dimmers Control LED Lights

Leading edge dimmers cut off the voltage at the beginning of the sin wave and trailing edge cut off the voltage at the end. This diagram shows the difference between leading edge and trailing edge.

Leading Edge vs Trailing Edge Sine Wave

Leading edge dimmers contain a coil and can buzz slightly. This can be annoying, particularly in a living room or bedroom Leading edge dimmers such as the Varilight V-Com are able to take much larger loads, even up to 600 watts on one switch.

What About ‘Trailing Edge’ Dimmers?

Trailing edge dimmers contain solid state components and are virtually silent. They tend to operate better for lower lighting loads of up to 100 watts of LED and some can dim just 1 LED. The latest Varilight V-Pro dimmer switch has zero minimum load.

But just because a dimmer switch is leading edge or trailing edge it doesn’t mean it’s an LED dimmer switch. Modern LED dimmer switches such as the Zano ZGRIDLED, Varilight V-Pro, V-Com or V-Pro Multi-Point and Hamilton Litestat are programmable. This means that you can tweak the settings of the dimmer to match the type of LEDs and the load (wattage) on the circuit. They've all been extensively tested to offer a broad range of dimming compatibility with the most popular LED lighting brands.

The Dimmer Switches We Sell Are Incredibly Advanced

Although the Varilght V-Pro looks like an ordinary dimmer switch with a rotary knob, it’s far from basic. The settings be easily adjusted by turning the knob in a sequence (click here to view the operating instructions).

This allows you to change the drive mode settings from leading edge to trailing edge. But the leading edge mode isn't true leading edge, its a modified leading edge with no TRIAC, that's why they also have the V-COM model which is true leading edge, born and bread. Other functions include the ability to trim off any nuisance flickering that might be happening. Flickering can sometimes still happen when the load is very low and when you attempt to dim the lights to a very low setting.

Why LED Lights Flicker & How To Solve This Problem

Dimmer switches struggle to detect that there is any load on the circuit which causes flickering, strobing or flashing to happen. With a programmable dimmer switch, you can trim off this and delete it from existence. This won’t allow you to dim the lights to a certain level of say 1-20% but it will solve your problem. This video below shows how easy it is to program the Varilight V-Pro:

Some minimum load or flickering issues can be solved by putting a resistive load on the circuit. One way of testing this before ordering one is to replace one of the LEDs on the circuit with a halogen. If the halogen stabilises the load, then the resistive load should work and resolve your problem.

Remember - Not All LED Lights Are Dimmable

Not all LED lights are dimmable, some manufactures still offer versions that are non-dimmable which cost slightly less. I once incorrectly predicted that all LED lights would become dimmable as standard, just like incandescent and halogens are, but this didn't happen as non dimmable are cheaper. In a price conscientious world the slight saving on offer has proven me wrong. Although this is happening more-so with integrated LED downlights. We state clearly on our website, which LEDs are dimmable and which ones are not.

Loading Advice & “De-Rating” Dimmers

An LED load is different to a halogen or incandescent due to its high inrush currents and current spikes. An LED load needs to be treated as if it’s much higher even though it consumes less energy. You either need to de-rate the dimmer switch or overrate the LED.

Some manufacturers recommend to de-rate the dimmer switch to 10% of its load, so a 400 watt dimmer would be rated at 40 watts when dimming LEDs. I’ve found this rule to be useless as it still doesn’t mean an LED will dim smoothly and 40 watts of LED doesn’t equate to many lights, it's not even 7x 6 watt LED downlights.

Varilight also had their own de-rating system but they've now rated all of their dimmer switches for LED loads to begin with. The V-Pro can dim up to 120 watts of LED and they have a high out V-Pro that can handle 300 watts. Something else to what out for is that the V-Pro will only dim between 1 and 10 dimmable LEDs. This is just a guide as I’ve known instances where up to 14 of the Aurora Ice 5W GU10 LED have been dimmed successfully but it does depend on the brand of LED that is used. The Aurora Ice 5W GU10 LED is a particularly good dimmable GU10 option that dims perfectly with home automation systems. Generally Aurora lights work well with home automation systems like Lutron and Lightwave. The Aurora MPRO works with Lutron Grafik Eye 3000 and the Grafik Eye QS which are both now discontinued.

Although the Varilight V-Pro no longer has a minimum load, it did used to be 10 watts for halogen and 2.5 watts for LED. Other brands have their own set of rules to follow as they play catch-up to Varilight.

Further Reading On LED Compatibility With Dimmer Switches

Even if you completely understand all of the science behind dimming and sine waves it still doesn’t mean you can successfully match an LED light to a dimmer switch. Some combinations are simply not compatible and don't work. We stick with only trusted lighting brands that we're familiar with and are happy to offer technical support about compatibility. We can easily liaise with the lighting manufacturer, or the dimmer switch manufacturers to check, or perform tests ourselves. Usually extensive testing has been done. Dimming LEDs isn't much of an issue these days. The main times you'll run into problems is when you upgrade from halogen to LED and expect your 1980s dimmer switch to handle an LED.

You can’t go too far wrong with the Varilight V-Pro for loads of up to 120 watts and the Varilight V-Com for loads of up to 600 watts they're the bullet proof universal dimmer switches. While Varilight continue to develop their dimmers, most lighting manufacturers use Varilight as the benchmark for dimming compatibility. The Collingwood Halers H2 Pro 550 for example, didn't used to work with Varilight, but its now been redesigned so it does.