Why does dimmable LED flash?

Susan Fernandez December 12 2021

Flickering of LED lights

LED lights have been known to have a certain flickering pattern that some people find annoying. In most cases, this effect goes unnoticed as the human eye can not detect such changes as it takes place as rapidly as at the speed of 1/200 of a second which is faster than an average blink taking place between 1/20 and 1/10 of a second.

Although LED strobe lights are mostly used outdoors in traffic signs, they also see usage indoors which includes automotive interiors and even homes. This kind of usage is becoming more common with time.

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However, the problem of flickering still persists especially if you live in houses where there are many lights installed interconnected through one switch or by having them present on different switches all over the house. If you use such kinds of lights indoors and you cannot avoid using 2 or more switches to control them, then this article is for you!

What causes LED flash and flickering?

The main problem that leads to LED flash and flickering is the fact that these lights use a lot of currents. When you turn on an LED light, it needs a start-up current that's about 10 times greater than the operating current. This start-up current can cause the LED to flicker.

Is it dangerous?

The most widely spread opinion is that LED flickering might damage your eyesight. However, it has recently been noticed that even though the light flickers at a high speed (1/200 of a second), the human eye only registers this change in case of rapid changes like when blinking or switching attention to another source of stimuli for example.

Some researchers have conducted research on strobe lights and found out that there are no reported cases of people being affected by the so-called "stroboscopic effect" which is related to some ocular disorders caused by quick fluctuations of luminosity. So strobing LEDs are a problem that requires solving and fast.

Why does it flicker even if the lights are off?

Since LED lights have a very high start-up current, the switch on your wall is not able to provide this much of a power surge required by the light. Thus, it's automatically supplied from the light's own voltage supply and that's why you see the flickering even when the lights are off!

What if I have all my LED lights flickering?

If all the LED lights in your house twinkle, then it is evident that the problem lies somewhere at your home's main power supply. The reason for this can be a faulty circuit breaker or even an internal wiring fault. In some cases, it could be the LED driver that is not working properly. This can lead to all sorts of trouble, but the most common one is your LEDs' early burnout.

Whatever the reason may be, it is best to get a professional to take a look at the problem and fix it for you.

Flashing vs Flickering - What's The Difference?

For those who are not familiar with the flickering term, let me give you a little introduction. Flickering is a rapid on-off of light. It can be described as the visible effect that is caused by the intermittent failure of a light source. This can be due to problems with the power supply, old or dirty lamps, or incorrect wiring.

On the other hand, flashing is an intentional turning on and off of lights for a specific purpose. It is often used as a signal, like in emergency situations or for indicating danger. For example, when you see the red lights on top of ambulances or police cars, they are flashing.

Now that we know the difference between LED flashing and flickering let's move on to how to dim our LED flashlight!

How to dim your LED Flashlight?

There are 2 types of LED flashlight dimming methods, passive and active. The passive method is the most common method as it does not require any additional investments from you. In addition, you do not even have to open your device in order to dim the light as with the case of the active method.

The only downside about this type of dimming is that it only allows for very limited incremental steps between on and full brightness (or vice versa).

Active dimming requires different components - potentiometers or variable resistors, transistors, and capacitors. It gives more results than the passive method but can be a more difficult task if you do not know what you are doing since there is a risk of damaging some parts inside your device if done incorrectly.

In general, if you have an LED flashlight and want to dim it, you can try one of the following methods:

Method 1 - Use A Smaller Battery

One way to dim your LED flashlight is by using a smaller battery. This will result in less power being supplied to the LED and therefore, it will be dimmer. You can try this if you have a battery that is not being used or if you have a spare one. All you have to do is insert the new battery and check if the light is still bright enough for your needs before replacing it with a larger one.

Method 2 - Add A Resistor In Series With The LED

For this method, you will need a resistor in series with the LED when powering up your flashlight. You can calculate the required resistance using Ohm's law  which states:

R = V / I,

where R expresses resistance in ohms, V has a voltage of your device measured in volts and I represents current also measured in amps. If your device cannot be powered directly from a 9V battery, then use an 8.2V battery and a resistor of about 620 ohms.

Method 3 - Add A Transistor And Capacitor In Parallel With The LED

This method is similar to the previous one but in this case, we will be adding a transistor and capacitor in parallel with the LED. The transistor will act as a switch to control the current flow while the capacitor will help to smooth out the power supply and reduce voltage fluctuations. You can use this method if you are not comfortable with soldering or if your device does not have enough space for a resistor.

How to prevent LED flicker?

There are 2 solutions you can use to fix this issue- make sure not to install too many lights interconnected through one switch and if possible use separate switches instead of interconnected ones.

If you have the first case where all the lights are connected using only one switch, try installing more light fixtures with separate switches alongside each other because there are no serious consequences of having them on different switches as opposed to having them on just one single switch. This solution is also commonly known as "decorator switching" which means that every switch will control a decorator item rather than having them controlled by one switch which will ultimately cause the lights to flicker.

The second solution is for those who cannot or do not want to install additional switches aside from what they already have. If this is your case, try redesigning your circuit. Chances are there that you might need more power lines coming in and out of the panel thus creating loop currents.

These loop currents can cause flickering issues. To fix this you should avoid using any loops especially between the light fixture and the switch box because if you use just one single line to go through all light fixtures then it eliminates the possibility of causing any loops resulting to smoother running electricity supply.

Flickering and bulbs - do they matter?

If you have a specific fixture, it is likely to be affected by the type of bulb that will be used. LEDs are more sensitive compared with other bulbs like fluorescents or incandescent which means that they will also easily cause flickering issues when installed on some fixtures. It is recommended not to use dimmer switches along with LEDs because they can cause flickering even more since most dimmers work best only with incandescent lamps.

If you still want to install an LED then consider using electronic low voltage (ELV) dimmers instead of magnetic low voltage (MLV) ones as ELV usually offers little resistance against LED flicker and does not require additional capacitors.

Additional tips - preventing LED flicker

To prevent LED flickers, you should not use dimmers that are too small for the number of lights installed. Also, dimming should be gradual- not fast because doing it abruptly may cause flickering issues to arise. Lastly, always make sure to check your circuitry and measure the voltage to avoid any unnecessary problems along the way.


LED lighting can be connected either in series or parallel. If you are not sure how to connect the lights, then consider consulting an expert before connecting them incorrectly. If you do it on your own without any guidance then at least make sure to keep the leads of each light together along with their positive and negative terminals so that everything is connected correctly especially when using parallel connections. This way, there will be no problems in terms of power distribution for all LEDs.

If you want to avoid LED flicker issues, there are simple solutions available such as installing additional switches or redesigning circuits which are commonly known as "decorator switching" since two switches are better than one switch when installed properly alongside each other.