What phone camera settings work best for the PWM flicker test?

Use your phone's standard camera app (not portrait mode). Disable auto-exposure if possible — on iPhone enable manual exposure by tapping and locking AE/AF. On Android enable Pro mode. Lower shutter speed (e.g. 1/120s) makes banding more visible.

My screen is always maximum brightness — does PWM still apply?

PWM dimming is typically only active below maximum brightness. At 100% brightness most monitors switch to continuous DC dimming. Test at 50–75% brightness for the most accurate results.

For most people, no. Sensitive individuals — particularly those prone to migraines, photosensitivity, or eye strain — may experience discomfort at PWM frequencies below 1000Hz, especially during long work sessions. Choosing a PWM-free or high-frequency (>1000Hz) monitor eliminates this risk entirely.

Primary tool

PWM Flicker Test

Select a frequency, go fullscreen, then film your screen with your phone.

PWM Flicker Test Online

Q: Can this tool detect PWM automatically?

The manual phone camera filming method is most reliable because it directly captures photons from the panel. Automatic webcam detection is experimental and requires a high-framerate camera (120fps+) which most laptop webcams do not have.

Check if your monitor uses PWM backlight dimming — a common cause of eye strain and headaches

60 Hz

Selected test frequency

Preview — click "Start Flicker Test" for fullscreen

How to test:

Set your monitor to 50–75% brightness (PWM is inactive at 100%).
Select a frequency above and click "Start Flicker Test".
Open your phone's camera app and point it at the screen.
Look for horizontal dark bands moving across the camera image.
If you see bands, tap "I See Banding" below. If not, tap "No Banding".

This test runs entirely in your browser. No data is collected or transmitted.

No Software

Runs entirely in your browser — nothing to install

Works at Any Brightness

Test at 50–75% brightness where PWM is most active

Phone Camera Method

Most reliable detection method — no special equipment needed

100% Free

No signup, no download, no limits on retesting

What Is PWM Dimming and Why Does It Cause Eye Strain?

PWM (Pulse Width Modulation) is a method monitors use to control brightness by rapidly switching the backlight on and off at a fixed frequency. Rather than continuously reducing the light output, the monitor flickers the backlight hundreds of times per second — if you choose 50% brightness with 240Hz PWM, the light is actually 100% on for half the time and completely off for the other half, cycling 240 times every second. To the conscious eye this looks like a smooth dimmed image, but the visual cortex and eye muscles are still processing each individual flash. Approximately 30% of LCD monitors on the market use PWM dimming below 1000 Hz. The alternative — DC dimming — reduces actual current to the backlight LEDs, producing a steady, flicker-free light at all brightness levels. OLED panels use a different approach but can also exhibit PWM at low brightness. If you experience headaches, eye fatigue, blurry text, or difficulty focusing after long screen sessions, PWM flicker from your monitor could be a contributing factor.

How to Use This PWM Flicker Test

The test uses a fast-alternating black-and-white canvas running in fullscreen mode. Your monitor's PWM frequency creates an interference pattern with the camera's rolling shutter or frame rate — when frequencies align, dark horizontal bands appear in the camera preview. Step 1: Reduce your monitor brightness to 50–75% (PWM is generally only active below maximum). Step 2: Select a test frequency that matches common PWM frequencies — 60Hz, 120Hz, and 240Hz cover the vast majority of consumer monitors. Step 3: Click "Start Flicker Test" and the tool goes fullscreen. Step 4: Open your phone's camera app and aim it at your monitor from about 30–50 cm away. Step 5: Look for dark horizontal bands moving slowly through the camera image — this is the interference pattern between the camera's shutter and the PWM cycle. Bands that move slowly or appear stationary indicate a frequency match. No bands means your monitor likely does not use PWM at that frequency. Try all five frequencies for a complete test.

PWM Symptoms: Headaches, Eye Fatigue, and Blurry Text

The sensitivity to PWM flicker varies significantly between individuals. Research suggests that people with a history of migraines, photosensitivity, or visual stress disorders are more likely to notice discomfort from PWM frequencies below 1000 Hz. Common reported symptoms include frontal headaches that worsen after 2–3 hours of screen use, a feeling of eye strain or dryness, difficulty reading small text (perceived blurriness caused by micro-saccades triggered by the flicker), and general fatigue. Many sufferers do not connect these symptoms to their monitor because the flicker is invisible to the naked eye under normal conditions. A simple diagnostic is to test the same workflow on a laptop OLED screen (which typically uses high-frequency PWM or DC dimming) and compare symptoms. If you feel significantly better on one display, the PWM profile of your primary monitor is likely a factor.

How to Find a PWM-Free Monitor

When shopping for a PWM-free monitor, look for displays explicitly certified as "Flicker-Free" by VESA or the manufacturer. ASUS, BenQ, LG, and Dell publish PWM specifications in their monitor technical datasheets — search for the monitor model followed by "PWM frequency" or look up the panel on RTINGS.com which measures backlight flicker directly with a photodiode. DC dimming is the gold standard — monitors using DC dimming control brightness by adjusting LED current rather than switching, producing zero flicker at any brightness level. OLED monitors often use high-frequency PWM (1000Hz+) which is generally imperceptible, though some users still report sensitivity. IPS panels from reputable brands in the "business" segment (targeting office productivity) are more likely to implement DC dimming than gaming-oriented TN or VA panels which prioritize response time. If you currently own a PWM monitor and cannot upgrade, keeping brightness at 100% eliminates PWM on most models, and using software like f.lux or Night Light to reduce color temperature at night avoids the need to lower hardware brightness.

Frequently Asked Questions

What phone camera settings work best?

Use your phone's standard camera app (not portrait mode). Disable auto-exposure if possible — on iPhone tap and hold to lock AE/AF. On Android enable Pro mode and lower the shutter speed to 1/120s. This makes banding more visible at lower PWM frequencies.

I see banding at 60Hz but not 120Hz — does that mean my monitor uses 60Hz PWM?

Yes — if banding appears at a specific frequency, that matches your monitor's PWM frequency. Banding is most visible when the test frequency matches or is a harmonic of the monitor's actual PWM cycle.

My screen is at maximum brightness — does PWM still apply?

PWM is typically only active below maximum brightness. At 100% most monitors switch to continuous DC dimming. Test at 50–75% brightness for the most accurate results.

Can this tool detect PWM automatically?

The manual filming method is most reliable. Automatic webcam detection is experimental and requires a camera capable of 120fps+, which most laptop webcams do not support. The phone camera method is accessible to everyone.

Is PWM harmful?

For most people no. Sensitive individuals — those prone to migraines or photosensitivity — may experience eye strain at PWM frequencies below 1000Hz, especially during long work sessions. Choosing a flicker-free or OLED display eliminates this risk.

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