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LEDs and Dimmers

By Ryan Iversen on 03/08/2019


LEDs and Dimmers

For most people, the use of a dimmer is a simple matter. Just wire it up to your light and it can dim. What most people don’t know is that was only true for just incandescent and halogen lights. Fluorescents, on the other hand, were known to be notoriously non-dimmable. But now with LED lights being the most popular light source on the market, people are being stumped by why the dimmers they have installed in their homes are not working with their new lights. To understand this problem, we’ll need to understand how dimmers work in relation with lights, including LEDs.

Now let’s first look at how the dimmers that have been installed in our homes for many years, work. These types of dimmers are now referred to technically as legacy dimmers. These dimmers were widely used and practically installed in every home in America. So, why do they work with incandescent lights and not LEDs? Part of that has to do with the dimmer and the other part with the light itself. How legacy dimmers work is because AC power flows in a cycle, the dimmers partially interrupt that cycle. This means for a moment the light doesn’t have power. Wouldn’t that mean the light should just turn off without power flowing through it?

Well yes and also no. While this is obviously the case with LEDs, and a reason as to why your LED light might be flickering, incandescent lights don’t face this problem. The simple reason as to why is unlike LEDs, incandescent lights have persistence. What this means is that even when there is no power flowing through it, your incandescent light will still glow because of all the heat it produces. Roughly estimated, 90% of the energy an incandescent light use is wasted as heat. While this lets them work with legacy dimmers, it is also the reason why they are being replaced by very energy efficient LEDs

The reason why LEDs don’t work well with legacy dimmers again has to do with persistence. A LED works by passing current through a semiconductor material and light is created from that. When the current stops, the LED stops producing light immediately. And therein lies why LED doesn’t work well with legacy dimmers. Because legacy dimmers stop the flow of current momentarily, the LED will turn off and then back on when the current resumes flow. If that is the case, then why are there dimmable LEDs? Dimmable LEDs can work with dimmers, just ones compatible with them.

Because of the growth of LEDs as the popular and efficient lighting source as they are, specially dimmers designed to work with them were developed. One of these was 0-10V dimmers. Originally designed for use with CFL lights, these lights use DC or direct current to dim lights. Instead of stopping and starting the current, these dimmers limit the amount of voltage that flows into the LEDs. This method works better because the LED will produce light with less brightness the less energy they have.

But just because LED dimmers can work with LEDs, it doesn’t mean that they are all compatible with each other. A dimmable LED comes with a list of dimmers that are compatible with it. Not every dimmer will be on that compatibility list. It is important that when you are installing dimmable LED lights or a dimmable LED fixture that you are using a dimmer that is compatible.

Product reference:

Dimmable G25 LED globe bulb 

Dimmable GU10 LED light bulb

Dimmable A19 LED light bulb

Dimmable 3-way A21 LED light bulb-2700K

Dimmable 3-way A21 LED light bulb-5000K