Why Do LED Lights Flicker On Video?

Take a look at the marvels of everyday technological inventions around you.

Your phone itself houses a dozen tools that we would be carrying around just a couple of decades ago, like cameras and calculators.

Sometimes, two tools created independently of each other can run into a little funny behavior when they interact.

These unexpected effects can also lead to more understanding of the science behind the working of the tools.

Today we will explore that science to make sure TikTokers are looking fine and dandy in their next video.

Sometimes it appears that an LED bulb, when viewed through a camera lens, flicks rapidly at regular intervals as if it is turning on and off.

LED bulbs are turning on and off, the flickering on video becomes more pronounced and obvious because the camera’s recording frames per second is unaligned with the frequency of electricity. This is called the ‘strobe effect’.

What Causes The Flickering Effect In The Video?

What if I tell you that LEDs don’t flicker on video, but they flicker all the time in real life?

Because that is exactly what happens. Our human eye cannot see the flickering of LEDs occur in front of us as it is just too fast.

To understand why the LED flickers on video, let me explain the pure science behind it.

LEDs are powered by alternating current, AC, in which electrons in the electricity move in and out of the circuit in cycles.

A cycle of electrons per second is called Hertz (Hz). In 1 cycle or Hertz, the light bulb actually turns off 2 times, as the electron alternates in and out.

In the US, electricity runs on 60 Hz, and in the rest of the world, it runs on 50 Hz. Which means the bulb is actually turning on and off between 100 to 120 times per second.

While our eye cannot see that flicker, seeing the LED through a camera lens makes the flickering obvious. We can see it happen on our screen as we record or playback a video.

Often, a camera opens and shuts its motion capturing shutter a little bit faster than the speed of a flickering LED.

When we see the LED on our screen flickering black for a split-second, that image got captured by the camera while the LED turned off in its current cycle.

When the frequency of the camera’s frame rate per second (FPS) and the LEDs don’t quite match, the flicker becomes visible on the camera screen.

Should I Be Worried That LED Doesn’t Work Properly?

The flickering of the lights has nothing to do with the quality or the condition of the LED bulbs. You can rest assured that, in fact, your LEDs are working in the way they are supposed to.

Your only concern should be when you can actually see the LEDs flicker with your own eyes. I have covered that issue in my article here.

Sometimes, when your eye cannot really see the flicker, and yet the LED is not flickering fast enough, your brain can still pick up this unnatural light effect and cause headaches, nausea and sight problems.

How To Stop LED Lights To Flicker In Video?

Since we know how the video camera picks up and shows flickering of LEDs, we can talk about how we can avoid this effect from getting picked up.

Undoubtedly, it can look pretty jarring and unsightly and greatly distract the viewer from your actual video content.

To avoid or at least reduce the flicker, you can do a number of things:

[su_note note_color=”#fbb534″]

  • Reducing the recording frames per second, the FPS, of the camera.
  • Adjusting the shutter speed: At 60 Hz so you will need a frame rate of 30p with a shutter speed divisible by 60 – 1/60, 1/120, etc. At 50 Hz, you need 25 FPS at a shutter speed like 1/50 or 1/100.
  • Moving closer or farther from the light, and adjusting the aperture accordingly.
  • Increasing or decreasing the brightness of the lights.

[/su_note]

All of these steps allow for the frequency of the AC current powering the LED to match as closely as possible to the FPS of the camera.

Even film restoration professionals face these issues, and in fact, here you can read about how Peter Jackson and his team had to manually adjust the shutter speeds as they restored a World War 1 footage that had a lot of flickering lights.

Keep in mind that flickering usually happens with LEDs connected to an AC supply, such as fairy lights.

Those LEDs that run on drivers that switch the current to direct current, or DC, don’t have this problem.

Some power supply drivers rectify the AC current from 50 or 60 Hz, increasing it up to 120 Hz, which becomes even hard for cameras to pick up, and fixes the problem.

Are you saying you have LEDs on DC power supply and are still running into this problem? In that case, your LEDs might be hooked onto pulse width modulation (PWM) for dimming setups.

With PWM, the LED again goes through periods of on and off cycles in the circuit, that can be captured by the camera as it records.

Do Incandescent Bulbs Flicker In Videos?

Incandescent bulbs also flicker at the same frequency as LED bulbs. But you would be hard-pressed to find a traditional bulb flickering on video!

This difference is due to the mechanics of how the two bulbs work.

While incandescent bulbs also run on AC current and turn on and off 100-120 times in a second, their filament wants to tell a different story.

Because the filament turns white-hot to emit heat, and as a by-product, light, the filament stays glowing hot long enough, even when the current is turned off.

The filament cannot heat up and cool down to zero 120 times in one second!

So, the residual heat of glowing hot filament makes it appear to be on. The overall effect is that incandescents don’t flicker on the video.

Final Words

Armed with this nifty knowledge of electricity frequency and unaligned frames per second, you can confidently deal with any strobe effect in your videos.

Have you seen any LEDs flickering on video set up with dimmers or on AC?

Does your camera or recording device have an adjustable shutter speed?

Leave a Comment

shares