Why Do LED Lights Flicker on a Dimmer Switch?

LED lights flickering on a dimmer switch is one of the most common issues homeowners experience after upgrading from halogen or incandescent bulbs to LEDs.  In most cases the issue will be between the compatibility between the bulb, the dimmer switch or the transformer/led driver. 

Pinpointing the reason as to why flickering is happening with the LED light can help you choose the right products and avoid future lighting problems.

Most flickering occurs when a LED bulb is used with an older dimmer switch because the dimmer switch was designed for incandescent or halogen bulbs.  Halogen or incandescent bulbs use much higher wattages than LED lights.  Traditional dimmers work by reducing the amount of power flowing to the bulb.   Incandescent bulbs can handle this easily because they use a heated filament.   LEDs use electronic drivers to regulate power.  If the dimmer and LED driver are incompatible, the power delivery becomes unstable, causing the light to flicker, pulse, buzz, or fail to dim smoothly.  Many old dimmers do not provide the type of electrical load LEDs need to operate correctly.

Common Causes of LED Flickering

1. An incompatible dimmer switch is by far the most common reason for a LED light flickering.  Many older dimmer switches require a minimum electrical load to function properly.  For example, an older dimmer switch may have been designed for a 60W–400W load.  Replacing several halogen bulbs with energy efficient LEDs might reduce the total load to only 20W.  Because the dimmer switch is operating below its designed range it struggles to regulate the current correctly which leads to flickering.
2. Not all LED bulbs are dimmable.  Unlike incandescent or halogen bulbs, not all LED bulbs are dimmable.  If the bulb is not dimmable it will flicker, flash or possibly will not work at all.  Any LED bulb that is dimmable will state this within the manufacturer information.  If it does not state this you should assume that the bulb is not dimmable.
3. Poor quality LED drivers can also lead to a LED light flickering.  A LED driver takes mains electricity and converts it to the needed voltage for the bulb.  Some LED bulbs are 240v and will not need to have a driver connected.  However there are LED lights which can be 12V or 24V.  Cheap or poorly designed LED drivers may struggle to handle the fluctuating power from a dimmer switch.  This can cause inconsistent brightness or visible flickering.
4. Leading-Edge vs Trailing-Edge Dimmers.  There are different types of dimmer technology available.  A Leading-edge dimmer is more commonly used with halogen and incandescent lighting.  It is not often that they are often compatible with LEDs.  Trailing-edge dimmers however are specifically designed to work better with LED lighting.  The type of dimming the dimmer switch does should be specified on the manufacturer’s specifications for the dimmer switch.  If you experience flickering and you have determined that the above reasons are not the cause, switching to a trailing-edge LED dimmer would be another thing to consider.
5. As we have stated above - a transformer/LED driver is used to convert mains voltage to the voltage needed for a light.  Transformer Compatibility is something else that can cause a LED bulb to flicker.  If you use a 24V transformer with a 12V bulb for example then this will overload the driver and the bulb possibly causing it to flicker.

Why Flickering Often Happens at Low Brightness

Many people notice flickering only when the lights are dimmed very low.  This happens because the dimmer is supplying very small bursts of power.  If a LED driver is faulty or poorly made it will not be able to regulate these tiny power levels consistently which will cause the light output to fluctuate visibly.  Higher quality bulbs and compatible dimmers usually reduce this problem significantly.

Can Flickering Damage LED Bulbs?

Occasional minor flickering is usually not dangerous and should not be a cause for concern, but persistent flickering can shorten the lifespan of both the bulb and the dimmer switch.  Addressing flickering early can help to protect your lighting system.  

The best solutions to prevent flickering will usually be:

• Use LED Compatible Dimmers.
• Replace older dimmers with modern LED-rated trailing-edge dimmers.
• Use LED Bulbs that state they are dimmable.
• Choose as high of a quality of bulb that you can.
• Check transformer compatibility making sure that the voltage and wattage load matches.

To summarise - LED flickering on dimmer switches is usually caused by compatibility problems between the dimmer, bulb, and driver technology.  Because LEDs use far less power than halogen or incandescent bulbs, older dimmer switches often struggle to control them properly.  Flickering is usually easy to fix by using dimmable LED bulbs and modern LED compatible dimmer switches.  Choosing high quality components and ensuring transformers and drivers are suitable for LED use will help create smooth, flicker-free lighting throughout your home or workplace.