Have you ever wondered why lamps, monitors, or car headlights sometimes flicker in your videos, which you recorded with your mobile phone, DSLR camera, or professional video camera? How does this effect, which can drive some videographers to despair, come about?
When viewed through a camera lens, a LED bulb can look like flickering rapidly every so often.
Here’s why this is happening. Due to the camera's frames per second being out of sync with the electrical frequency, LED bulbs are turning on and off, causing the video to appear to flicker. It is known as the strobe effect.
Flickering in videos: What causes it?
Even when LEDs don't flicker on video, they do flicker in real life. It is just too fast for the human eye to see LED flickering in front of us. Let’s take a look at why the LED flickers on video.
Light-emitting diodes (LEDs) are powered by alternating current, AC, in which electrons travel in and out of a circuit in cycles.
All electronic devices are operated with a certain mains voltage. In Europe, the mains voltage is 230 volts at a mains frequency of 50 Hertz. In North America, all public electricity networks run at a frequency of 60Hz. Why the network frequency is not uniform worldwide has no technical, but historical background.
When shooting, you usually choose the camera settings so that it meets the quality requirements and that the final image runs smoothly on our monitors afterward. The shutter in the camera, which is responsible for the exposure time or shutter speed, has an influence on the latter.
Professional video cameras allow the shutter to be switched. In the example of a 75 Hz monitor, a shutter of 1/75 would be necessary. In most cases, however, the normal exposure times are not sufficient to counteract the flickering.
In this case, some film cameras have a step-less shutter setting to avoid flickering effects. This function is called the CLS function, or "Clear Scan Function".
Here’s why flickering is visible on the camera
Motion-capturing shutters of cameras usually open and close faster than the rate at which an LED flickers. The flickering can't be seen with the naked eye, but through a camera lens, the flickering is more apparent. As a result of a mismatch between the frequency of the camera's frame rate per second (FPS) and the LED frequency, a flicker appears on the camera's screen.
Does flickering mean that LED is not functioning properly?
The LED bulbs flicker for no reason related to their quality or condition. You should only be worried if you can see the LEDs glimmering in real life, and not on the screen. This disturbing light effect can cause headaches, sleep problems, and even poor eyesight.
How to reduce the LED flickering on video?
There are several things you can do to avoid that annoying effect:
- By lowering the FPS of the camera, the camera records fewer frames per second.
- Shutter speed adjustment: At 60 Hz, you will need a frame rate of 30p and a shutter speed divisible by 60.
- You can experiment by increasing or decreasing the brightness of the LED lights.
As a result of all of these steps, the AC current used to power the LED matches its frequency as closely as possible to the FPS of the camera.