Have you ever shot a video with your phone or camera in a bright LED-lit room, checked the results, and noticed the screen is flickering like crazy? LED lights cause the so-called stroboscopic effect. LED lights turn on and off quickly all the time, but our eyes are too slow to perceive it. For you, light is a continuous thing, but cameras work differently. A video may look smooth, but it’s nothing more than a collection of individual photos in a sequence captured at a higher frame rate, such as 24 frames per second (FPS).
Specifically, LED flickering occurs when the FPS captured by your camera is not aligned with the frequency of electricity. This becomes even more pronounced if you’re shooting slow-motion video (recorded at 120 or 240 FPS on iPhones, for example). Fortunately, there is a solution to this. Adjusting the FPS of the recording can eliminate this annoying effect, as can changing the shutter speed or, in some cases, replacing the bulbs themselves.
The Science Behind Glitter
At the heart of flickering is alternating current (AC). Thanks to it, the electrons pass through the current in cycles. One cycle per second is measured in hertz (Hz). Hypothetically, in a Hz or a single cycle, the current changes direction once, so the bulb flashes twice as the electrons come and go.
In the United States, electricity has a frequency of 60 Hz. This means that in a single second, the light bulb has technically turned off and on 120 times. The human eye (and our glorious brain) perceives events continuously. In other words, we don’t treat the environment as a series of still images. Once the flicker exceeds a certain speed, our brains simply no longer register it.
The cameras are different. When recording video, the camera shutter opens and closes much faster than the LED light pulses. In other words, the black flicker you captured occurred exactly when the LED light turns off during its regular cycle. So when a camera and the lights are out of sync, or when the shutter speed doesn’t match the flickering of the LEDs, your video will clearly capture the dreaded strobe effect. While this makes sense for cameras with a physical shutter, what about phones? They use an electronic roller shutter that exposes the sensor line by line, so this flicker can also be seen on these devices. You can also change settings to avoid errors that could make your images look worse.
How to eliminate LED flickering on videos?
If you notice LED lights blinking on your camera, your first line of defense is to adjust the FPS and shutter speed. This is where some professional filmmaking standards come in handy, particularly the 180 degree rule. If you set the FPS to 30, your shutter speed should be twice that amount, or 1/60. Set your FPS to 60 and the shutter speed should be 1/120, and so on.
It is helpful to keep this setting as low as possible, if possible. Since the power in the United States is 60 Hz, the light flashes 120 times per second. Setting your shutter speed to whatever matches that speed is a good idea. A shutter speed of 1/60 will work just fine, but you can also double it to 1/120. As long as the shutter speed is divisible by 60, you’re fine. Just keep in mind that regular phone cameras, for the most part, don’t have shutter speed control for video. Although you can get more “professional” control using third-party apps, dedicated video cameras, such as camcorders, still reign supreme in terms of manual control.
If all else fails, replacing the bulbs themselves could eliminate the flickering. An online user reported that the LED lights flicker when using the slow motion feature on the iPhone. To overcome this conundrum, they replaced their existing bulbs with non-flickering variants from Amazon and, surprisingly, the images brightened. Setting up your own non-flickering LED lights could eliminate the flickering problem without the need to adjust your camera settings.
