FAQ: Why do LED Lights Flicker?

Why do LEDs flicker

At Downlights.co.uk there's nothing more in life that we dislike than flickering LED lights. When the modern LED arrived on the lighting scene dimming them used to be quite tricky but these days flickering has been eradicated. Here are our 5 top tips to stop LEDs from flickering or strobing.

1. The LED isn't Dimmable

This might sound obvious to some, but not all LEDs are dimmable. In the early days of LED technology, dimmable LEDs cost a lot more to buy, even up to 4 times the price and only the best lighting brands such as Philips had dimmable options. Its worth double checking that the LEDs you've purchased are in fact dimmable.

2. Check Your Dimmer Switch is LED Compatible

If you try to dim an LED with an old dimmer, which is usually an inductive dimmer you'll most likely experience flickering which will increase the lower you attempt to dim it. Modern LED compatible dimmer switches such as the Varilight V-Pro is programmable. It has settings that allow you to fine tune the dimming settings based on the LED load on each circuit. The V-Pro has trailing edge and a synthesized leading edge setting which can be changed by rotating the knob and pressing it in a specific sequence. If your LEDs are flickering with a Varilight V-Pro you can change the settings.

3. 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 often 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 no minimum load, it used to be 10W, then 2.5W and now its zero. This means it can dim just one very low wattage GU10 LED or LED downlight.

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 6W 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 with home automation systems.

4. Maximum Quantity of LEDs isn't Within the Range

Although the Varilight V-Pro is one of the best LED dimmer switches on the market, it is limited to how many LEDs you can dim per per switch. With a maximum range of 1-10 LEDs, it's usually suitable for most room types, but if you need to dim more, Varilight also offer higher output versions which dim up to 30 LEDs. The standard V-Pro also has a maximum wattage of 120W, so make sure you also don't go over that.

5. The Dimmer Switch & LED isn't Compatible

Just because a lighting manufacturer say to use a leading edge or trailing edge dimmer switch doesn't necessarily mean it will work. A leading edge dimmer switch from one company will give you totally different results from a leading edge dimmer switch from another company. In the early days of LED lighting even using the same dimmer switch from the same company, with the same product code could produce different results with the same type and amount of LEDs.

If the wattage rating of the dimmer switch is 250W or 400W, its rated for incandescent an will need to be de-rated for use use with LEDs. For example a 6W GU10 should be classed as 20W 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 of 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. Modern dimmer switches and control systems shouldn't flicker or buzz as they've been purposely designed to work with LEDs.

Watch out for MR16 LEDs, if you've got a low voltage halogens and are looking to upgrade, its best to replace them with GU10s. Otherwise you'll also need to make sure the transformer is LED compatible. This can be particularly difficult when you're dimming them as all of the components need to be able to work together in harmony.

There are many other more scientific reasons that cause LEDs to flicker; understanding them won't necessarily 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.