Why Do LED Lamps Flicker?

why do led lamps flicker
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When you think of lights flickering overhead, the first thing that comes to mind might be an old library or a horror film. One thing that these places usually have in common is long arrays of fluorescent bulbs that are long past their expiration date.

More recently, LED lights have been rapidly replacing fluorescent lights as the lighting of choice. Although flickering occurs much less with LED lighting than with fluorescent lighting, it still happens from time to time. So, why do LED lamps flicker, and what can you do to solve this problem?

Different Kinds of Flickering

There are two different kinds of flickering when it comes to lights: invisible flicker and visible flicker. Visible flicker is the kind of flicker that is perceptible by the human eye. Invisible flicker cannot be seen but can still be sensed by the human body.

Visible Flicker

Visible flickering is any sort of flickering that occurs below a frequency of 100 Hz. Anything below this frequency can be detected by the human eye.

Visible flickering is a cause for concern when it comes to matters of health. Exposure to visible flickering at frequencies in the range of 3 Hz to 70 Hz for even a short time can cause epileptic seizures. However, the greatest possibility for the occurrence of seizures happens with flickering frequencies between 15 Hz and 20 Hz.

Because one in four thousand people suffer from photosensitive epileptic seizures, visible flickering constitutes a public health and safety issue. There may be many other people who suffer from this condition but have not yet been officially diagnosed with it.

Invisible Flicker

Invisible flicker is flickering that is present but which cannot be seen with the naked eye. This is any flickering that has a frequency of greater than 100 Hz.

Although it is not visible to the naked eye, invisible flickering can still be sensed by the human body and can still have a detrimental effect on a person’s health and wellness.

Negative health effects of invisible flickering include the following symptoms: dizziness, headaches, eye strain, impaired thought, migraines, and other overall symptoms of feeling sick or unwell.

What Is the Origin of Flickering?

In order to obtain a better understanding of the flickering of lights, you can take some time to think about the concept of strobe lighting, which is a theatrical effect produced intentionally.

Intentional Flickering

Strobe lighting is an intentional flickering effect, during which light is emitted at particular frequencies. This causes your brain to view moving objects as though they are moving in slow motion.

Strobe lighting occurs at frequencies that usually equate to a couple of flashes every second. However, these frequencies are fairly close to those that are responsible for causing epileptic seizures.

Movies in theaters or television shows that have scenes with this kind of strobe lighting effect will often have a public health announcement warning of the potential for causing epileptic seizures or stroke.

Unintentional Flickering

Lighting equipment that flickers without being designed with that intent can trace its origin back to the electricity companies that designed the flow of electricity to utilize alternating current, or AC, in the place of direct current, or DC.

Alternating current has a sine wave, which peaks both negatively and positively, switching back and forth numerous times in a second. This causes it to be in a range in which flickering, or even sometimes an audible hum, occurs.

To make matters clear, all lights powered by alternating current (the standard form of household electricity) will flicker, whether they are halogen, incandescent, fluorescent, or LED lights. However, flickering was much less noticeable with the old incandescent light bulbs, because the residual heat from the light bulb caused the bulb filament to continue glowing between each flicker or current change.

Traditional incandescent light bulbs were actually very inefficient because of this residual heat, losing approximately 90 percent of the energy, which was directed into them in the form of residual heat.

Why Do LED Lamps Flicker?

The flickering of LED lights is, as was described above, caused by the alternating current of your electricity supply. All lights that are connected to a standard electricity source flicker. It is just that the flickering of some light sources, such as LED light bulbs, is much more noticeable than the flickering of other light sources, such as incandescent light bulbs.

What makes LED lights so energy efficient is also what makes their flickering more noticeable. Unlike incandescent lights, halogen lights, and fluorescent lights, LED lights have no persistence. The switching off of the power source to an LED light causes the light output to stop instantly, without any persisting glow from residual heat.

Thus, if an LED light is directly connected to an alternating current electricity supply, the LED bulb will switch on and off 60 times each second. This is a frequency that is slow enough to be visible to the naked human eye.

This is why a number of people believe that LED light bulbs flicker more often than older or traditional light bulbs. This used to be the case in the past, but it is no longer true in this day and age.

Why Modern LED Lighting Should Not Flicker

The flickering of LED lights is no longer a problem for modern installations of LED lighting. This is due to the fact that LED lights are no longer directly connected to the main electricity supply.

LED lights are instead powered by a specially designed LED driver, which transforms voltage and converts the alternating current into direct current to eliminate flicker.

why do led lamps flicker

Choosing the Right LED Driver

Modern LED lights require a direct current instead of an alternating current electricity supply. The method you use to power your LED lighting can potentially eliminate the possibility of LED flicker.

An LED driver or power supply is also known as an LED transformer, but such an LED driver does more than to step down or transform the voltage. A proper LED driver will convert the alternating current into a direct current.

If you select a proper LED driver or power supply, your LED lighting will be supplied with a constant current, and the light will not flicker.

The Effects of a Cheap LED Driver

If you choose to buy a no-frills, cheaper LED driver of a lower quality, it may not necessarily provide a constant current for your LED light bulbs. It may simply convert the alternating current to direct current to produce an oscillating current, one which generally causes the input voltage frequency to double.

This doubles the potential frequency of flickering, from 60 Hz to 120 Hz. This moves the flickering beyond the visible range into the invisible range, since flickering at 120 Hz is not noticeable by the human eye.

Although most humans can see flickering only if it occurs at a range of 100 Hz or below, there are still some people who can detect this faster flickering with their eyes. However, even if you are not in this small category, your health may still be negatively affected by invisible flicker, as was described earlier.

The Effects of a High-Quality LED Driver

If you are willing to spend more money on a high-quality LED driver, then it is possible for you to eliminate LED lighting flicker entirely, instead of merely moving it into the invisible range. You can do this by purchasing a power source that supplies a constant current.

Such LED drivers, which are of a higher quality and are built to higher specifications, can virtually eliminate flicker. They vary the voltage by removing the peaks of the sine wave across the electric circuit. This generates an electric current that is constant.

This means that the driver will deliver only a constant current, without any fluctuation, to your LED lighting. This eliminates the oscillating current, which was the effect of the conversion from alternating current to direct current.

Unfortunately, an LED driver designed to supply a constant current cannot completely eliminate flicker in every situation. If your control circuitry, power supply, and LED products have some incompatibility issues, this may cause flickering that cannot be solved even by a high-end LED driver.

What Is the Cause of Regular, Rhythmic Flickering?

Flickering that is caused by the incompatibility of your components will most likely be uneven and irregular. However, if your LED lights flicker in a rhythmic, regular fashion (for instance, each second), then the reason is probably that your LED power supply is not giving enough power to your LEDs.

Such regular flickering is a part of the warning system of high-quality LED drivers. It is intended to indicate that the LED lights are drawing more power than the driver can supply. This problem can usually be solved with a bigger, more powerful LED power supply.

Dimming as the Main Cause of LED Flickering

For many LED installations and lighting projects in the present day, the implementation of a dimmer or dimming function is the single most common cause of visible flicker. Dimming may cause problems in an LED lighting system that is otherwise perfectly installed and executed.

The reason for this is that most conventional dimmers function by extending the “off” segment of each switch on and off cycle of flickering. This reduces the total output of light, resulting in a dimming effect.

This dimming technique is known as pulse width modulation (PWM). PWM functions quite effectively as long as the frequency of switching does not drop to the level that the human eye can detect.

Solutions for Flickering Caused by Dimming

Manufacturers of dimmers are attempting to solve the problem by making dimmers for LED lights with significantly faster cycles of flickering (aiming for 1000 Hz).

Unfortunately, the higher flicker frequency means that your LEDs need to be much nearer to your power transformer. This is not always practical or convenient, but if this is not a problem for you, you can buy one of these specialized LED dimmers.

There is a simple alternative to purchasing those more expensive, less flexible LED dimmers. You can avoid the flicker generated by PWM simply by not dimming your lights too much. If you dim your lights less, the flicker cycle will not be made visible to the naked eye.

Because dimmers have improved in recent years, you can now dim LED lights more than 50% of the way without experiencing flicker. In some cases, you can even dim the lights all the way without producing visible flicker.

Conclusion

Why do LED lamps flicker? LED lights are much more energy-efficient than other forms of lighting. However, they still flicker, and sometimes the flicker is more noticeable than in traditional lighting forms. This is because LED lighting has no persistence or residual glow to mask the flickering.

To solve LED flicker, choose a high-quality LED power supply or driver, preferably one that supplies a constant current. Make sure that your LED setup is compatible with your power supply and control circuit. Lastly, consider buying a specialized LED dimmer or not going below a certain level of dimness.

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