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LEDs, Why Do They Flicker?

By Ryan Iversen on 02/26/2019


LEDs, Why Do They Flicker?

Flickering lights are an annoyance for many people. They can distract, annoy and for some, cause a medical emergency. For many years, fluorescent lights were the main example and source of the flickering light problem. When prices for LED lights began to drop, they quickly started to replace fluorescents in their many applications. Many thought this would be the end of the wide seen flickering light problem. But LEDs also started to flicker and many are asking why and how this is happening. Hopefully today, the light will be shed on the subject.

Before we discuss what causes flickering in LEDs, we have to go over the two types of flickering and how they can both affect you. The first and most obvious type of flickering is visible flicker. This is the flickering we all know and dislike. Not only is it distracting, but it can cause seizures for those who have photosensitive epilepsy. The other is less known because we simply can’t see it. Invisible flickering is called as such as the light is flashing on and off faster than the human eye can perceive.

To some people, invisible flickering is an even worse problem than visible flickering. Have you ever felt sick or dizzy for no reason at all in the workplace or where fluorescent lights and their LED equivalents are used? If yes, then that was because of invisible flickering. Not only does it cause a general sick-feeling and dizziness, but it can also cause eyestrain, headaches, migraines and impaired thought. Now that we went over the two types of flickering, it’s time to discuss why flickering happens in LEDs.

A common cause that LED flickering can be traced back to is the source of our electricity. Our power companies have designed electricity flow to use alternating current or AC. As opposed to direct current (DC), AC power changes the direction of the electricity flow periodically. This results in AC power flowing in something called a sine wave. These sine waves peak both positively and negatively and these peaks can result in flickering. This problem is more pronounced in smaller voltage LEDs like strip lights when they are wired directly to the main power supply.

Another source of flickering is simply incompatible switches. Many of the switches we have in our homes that have been there for years are just not designed for LEDs. The worst cause of this is dimmer switches. Most dimmers not designed to work with LEDs operate by the process of phase cutting. This means that they reduce the voltage entering the light. For AC power, this means shortening the waves that the power travels in, giving them a longer “off” and a shorter “on”. This doesn’t work well with LEDs as they aren’t designed with persistence. What that means unlike with an incandescent, when the LED has no power, it is simply off instead of the excess power keeping it lit like in an incandescent. Doing this will amplify the flickering of an LED that is running on AC power and can lead to a lack of startup power.

But there are some LEDs designed to work around this and they still flicker. This is probably because of a bad connection or it could be a result of a little device install in many outdoor LED lights, the photocell. How a photocell works is that based on the level of ambient light entering it, it can either stop or allow power to flow to the light. This is why lights that have a photocell built into them stay off during the day. But this photocell can also be the cause of why your outdoor light is flickering. Any light of certain level, regardless of their source, can trip the photocell. The light of your fixture being reflected or even the light from another fixture near it can cause the photocell to turn the light off. In the case of the reflective surface, the light from the fixture will turn it off and on again as light tricks the photocell. For the case of two lights near each other with photocells, they will cause each other to flicker on and off in a cycle.

Now that we have gone over the most common causes, the question remains, how do we fix this? The good news is that each one of these causes has a way you can solve the problem. For the issue of current, many strip lights come with a power adapter that plugs into the wall and converts the power into constant current. This constant current is DC power and greatly reduces the chance of your LEDs flickering. DC power transformers for strip lights can be purchased as well if you so desire. The switches, on the other hand, are a little more time and monetarily consuming to fix. The best way to fix LED lights flickering caused by incompatible switches is to replace them with switches that are designed to work with LEDs.

For the photocell related problems, you can go about it a few different ways. If you can, removing the reflective surface will solve the problem of reflected light causing your fixture to flicker. If the surface in question can’t be removed because of various reasons, then it is better to just simply move the light to a new location. Moving the light also works for the case of the two lights that are causing each other to flicker. But the easiest and by far the less time-consuming method to deal with flickering caused by photocells is to use a photocell cover. These covers work by either completely stopping all light from entering the photocell or only letting light enter from a certain direction or angle.

In the end, LED flickering is a problem, but one that can be dealt with. With the information given to you, hopefully flickering lights will no longer be an issue you have to deal with.

Product reference:

Dimmable A19 LED light bulb


Dimmable G25 LED globe bulb


Dimmable GU10 LED light bulb