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5-Second Scan

Flicker & Shutter Frequency Scanner

A slow brightness pulse or rolling band under artificial light is not your imagination — it is your camera's shutter and your lighting's mains frequency landing slightly out of step. This watches your feed for exactly that pattern, scores how visible it actually is, and estimates whether the light behind it is running on 50Hz or 60Hz power.

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Status

Scan

Click "Start Scan", point the camera at the light source you want to check, and hold still for about five seconds.

Readout

Flicker Severity & Mains Frequency Results

No flickerSevere
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/ 100
Flicker Severity

Details

  • Verdict:—
  • Beat Frequency:—
  • Camera Frame Rate:—

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Notes

Why this happens

Mains power does not deliver a constant brightness — light output pulses at twice the AC frequency, which is 100 times a second on 50Hz power and 120 times a second on 60Hz power. Human eyes rarely notice this directly, but a camera samples the world in discrete frames, and when its frame rate does not divide evenly into the light's pulse rate, each successive frame lands at a slightly different point in the pulse cycle. That drift is what shows up as a slow rolling band or overall brightness pulse on camera even though nothing in the room looks like it is flickering to the naked eye.

This is also why the same light can look perfectly clean on one camera and badly flickery on another — it comes down to whether that specific frame rate happens to line up with that specific mains frequency, not the light bulb alone.

How the estimate works

The severity score comes directly from measuring how strongly your brightness is oscillating and how regularly it repeats — that part is a direct measurement and is reliable. The 50Hz-vs-60Hz call is an inference: this scanner calculates what beat frequency each hypothesis would produce at your camera's actual frame rate, then reports whichever prediction is closer to what it actually measured. Both predicted values are shown next to your result so you can check the reasoning yourself rather than take a black-box guess.

Fixing it

Check your camera app or driver firstMany webcams and OS camera settings include an explicit "power line frequency" or "anti-flicker" option. Setting it to match your region often removes the problem instantly with no new hardware.
Swap the bulb, not the cameraDC-driven or good-quality flicker-free LED fixtures do not have an AC cycle to alias against in the first place. Cheap dimmable LEDs with PWM drivers are the most common offenders.
Traveling internationally?If your camera's anti-flicker setting was configured for the wrong region's mains frequency, this is the first thing to check after a bad flicker result post-travel.

Benchmark Reference

Severity Score at a Glance

GradeSeverity scoreVisible on calls?
Clean< 8No — not meaningfully present.
Mild8 – 34Usually not noticeable to viewers.
Significant≥ 35Likely visible banding or pulsing.

The severity number is a direct measurement of oscillation strength; the 50Hz/60Hz call alongside it is the tool's best inference, shown with both predictions so you can check the reasoning.

Step-by-Step

How to Run the Test

  1. Click "Start" and allow camera access when prompted.
  2. Point your camera at the light source you suspect is flickering, or your normal call background under normal lighting.
  3. Hold still for a few seconds while the tool samples brightness across multiple frames.
  4. Read your severity score and the 50Hz/60Hz estimate, then check your camera's anti-flicker setting if the result is significant.

Common Questions

Frequently Asked Questions

What causes webcam flicker or banding?
Mains-powered lighting pulses at twice the AC frequency — 100Hz on 50Hz power, 120Hz on 60Hz power. Your camera samples the world at its own frame rate, and when that rate does not line up neatly with the light's pulse rate, consecutive frames catch different brightness levels, which shows up as a slow rolling band or pulse.
How do I know if my flicker is 50Hz or 60Hz?
This scanner estimates it by comparing the beat frequency it measures against what each hypothesis predicts for your camera's actual frame rate, and shows both predictions next to the measurement. Many webcams also let you set a power-line frequency manually in their driver or OS camera settings, which is worth checking directly if the estimate is inconclusive.
How do I fix webcam flicker?
First check whether your camera app or OS has an explicit anti-flicker or power-line frequency setting and match it to your region's mains frequency. If that option is not available, switching to DC-driven or high-quality flicker-free LED lighting removes the pulsing at the source, since there is no longer an AC cycle to alias against.
Why do only some lights cause flicker?
Incandescent bulbs have enough thermal lag that the filament never fully dims between AC cycles, so the pulsing is mild. Fluorescent tubes and cheap dimmable LEDs using PWM drivers switch on and off far more abruptly, which produces a much stronger, more camera-visible pulse at the same underlying frequency.
Camera access blocked — how do I fix it?
Click the camera icon in your browser's address bar to confirm this site is allowed, or check your OS's camera privacy settings if the browser already shows it as granted.