FAQ: Why do LED Lights Flicker?

Why do LED Lights Flicker?

In short, the two main reasons that cause LEDs to flicker are:

The minimum load of the dimmer switch is not met

Most dimmer switches (mainly leading edge) have a minimum load of 40 watts, if this load is not met then flickering may occur. Flickering will be more noticeable at lower levels, IE when attempting to dim down below 50%. One way of solving this problem is to use a resistive (or dummy) load. A resistive load fools the dimmer switch into believing that there is enough load on the circuit and sometimes solves the problem.

Another way is to use an LED dimmer switch; this type of dimmer switch has been tested almost specifically for use with LEDs and has a lower minimum load. The Varilight V-Pro range has a minimum load of just 2.5 watts when used with LEDs. This means it can potentially dim just one GU10 LED or LED downlight. Although Varilight now recommend using 2-10 LEDs per switch.

However, some lighting control systems such as the Lutron Grafik Eye QS have a minimum load of 40 watts but we've successfully dimmed one 6 watt Megaman GU10 right down to 1%. Often the minimum load value is a guide and was originally intended for halogens, not LED. Often with LEDs the rule book goes out the window and it's more a case of testing each combination as you go along. This is the reason we stick with high quality lighting brands such as Philips and Aurora that we've sold and tested for many years.

Sometimes using a resistive load can resolve this issue. The Danlers RESLOADE works particularly well in combination with Lutron Rania dimmers and GU10 LEDs such as the Megaman 6W. The Lutron Rania range of dimmer switches allows you to select between trailing edge and leading edge functions and if you do experience flickering when you dim the lights down low, you can 'trim off' the flickering.

  • More commonly, the combination of dimmer switch and LED is not compatible.

    Just because a lighting manufacturer such as Philips or Megaman (for example) say to use a leading edge or trailing edge dimmer switch doesn't mean it will work. You need to know specifically which one to use as they are all different, a leading edge dimmer switch from one company will give you totally different results from a leading edge dimmer switch from another company.

    Even using the same dimmer switch from the same company with the same product code can give different results with the same type and amount of LEDs. You also need to make sure the batch codes are the same or flickering may occur.

    And did you know that you may need to de-rate the dimmer switch or over-rate the LED? For example the Megaman 6W GU10 should be classed as 20 watt on trailing edge circuits and 60W on leading edge circuits. This is important when using automated lighting systems such as Lutron, Rako or Crestron etc. The over-rating of LEDs is needed due to current spikes and has to be calculated using an oscilloscope. Lutron are able to do these tests if you ask them nicely and send them the samples.

Buzzing LEDs

Another problem sometimes associated with LED lighting is buzzing noises. Some components like dimmer switches, LED drivers and LED bulbs buzz when you try to do dim them. This is usually caused by incompatibility although some types dimmer switches, mainly leading edge dimmers make a buzzing noise as they are fitted with a small coil.

We've known some instances when trying to dim MR16 LEDs with the Lutron Grafik Eye which is leading edge as standard. To combat LEDs buzzing you can install a lighting filter which smooths out the waveform and reduces buzzing. This item can also allow more lights to be dimmed per zone which can save you a lot of money when you consider how much it costs per zone.

This lighting filter is available to order by clicking on the image below:

Although if you're planning a new Grafik Eye installation we don't recommend using MR16s because by the time you've purchased them plus the transformers, plus the lighting filter it would be far easier and more cost effective to use GU10 such as the Megaman 6W or an integrated LED such as the EcoLED ZEP1 which work fine.

We regularly monitor and test our dimmer switches and make sure we have the very latest batch codes that work perfectly well with the LEDs we sell.

Follow the link below to view our range of LED compatible dimmer switches:

There are many other more scientific reasons that cause LEDs to flicker; none of these will solve your problems but to find out more view the 15 page 'Controlling LEDs' white paper from Lutron or feel free to contact us for more information on: 01706 868343. We can't offer information on cheaper unbranded LEDs such as SMD as we don't sell or test them.