LEDs often appear to pulse or flash on camera because of a mismatch between how LEDs are powered and how cameras capture light over time. To the human eye, the light looks steady, but cameras can reveal what’s really happening.
The main reasons are:
1. LED power isn’t truly constant
Most LEDs are not powered by a smooth, continuous current. Instead, they’re driven by:
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AC power (which oscillates at 50 Hz in Canada), or
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Pulse-width modulation (PWM), where the LED rapidly switches on and off to control brightness
This flickering happens so fast that your eyes average it out, but a camera can detect it.
2. Rolling shutter in cameras
Many phone and digital cameras use a rolling shutter, meaning:
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The image sensor is scanned line by line rather than all at once
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Each line captures the LED at a slightly different moment
If the LED brightness changes during that scan, the result is visible bands, pulses, or flashing in the recorded image.
3. Frame rate vs. flicker frequency
If the camera’s frame rate (for example, 30 or 60 frames per second) doesn’t align with the LED’s flicker frequency, the camera captures different brightness levels in each frame, creating an apparent pulsing effect.
4. High-speed switching reveals hidden flicker
Some LEDs switch thousands of times per second. While invisible to humans, fast camera shutters or slow-motion video can make this flicker very obvious.
Why your eyes don’t notice
Your visual system has persistence and smoothing built in. As long as the flicker is above roughly 60–90 Hz, it appears continuous to most people.
How to reduce the effect on camera
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Use flicker-free LED lights designed for video
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Match camera settings to local power frequency (50 Hz in Canada)
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Increase shutter speed or use a global shutter camera
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Avoid dimming LEDs that use low-frequency PWM
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