How to Check If Your Phone Uses PWM Dimming

PWM (pulse-width modulation) dimming is a common technique for controlling screen brightness on OLED and some LCD phones. It works by rapidly turning the backlight or pixels on and off, which can cause eye strain or headaches in sensitive people. This guide shows you how to determine if your phone uses PWM dimming using simple methods, so you can make informed decisions about your device.

What You’ll Need

• Your phone (the one you want to test)
• A second camera (another phone, a digital camera, or a webcam) – a phone camera works best
• A computer or another screen to view the test footage (optional but helpful)
• A dark room or dimly lit area (to make the effect more visible)

Step-by-Step

1. Understand what PWM looks like. When you view a PWM screen through a camera, you’ll see horizontal or vertical dark bands scrolling across the display. These bands are the flicker caused by the screen turning on and off. The bands may move slowly or appear static depending on the refresh rate and shutter speed.
2. Set up your test environment. Go to a dark or dimly lit room. Turn off any bright lights that might interfere with the camera’s ability to detect the flicker. Keep the phone you’re testing at a comfortable viewing distance.
3. Open the camera app on your second phone. Use the rear camera if possible, as it usually has a higher frame rate and better low-light performance. If you’re using a dedicated camera, set it to video mode.
4. Point the camera at the screen of the phone you’re testing. Make sure the screen fills most of the camera’s view. The screen should be showing something bright, like a white or light-colored image, to make the flicker more apparent.
5. Adjust the brightness of the test phone. Set the screen brightness to a low or medium level (around 20-50%). PWM is often more visible at lower brightness settings. If you have auto-brightness on, turn it off so the brightness stays constant.
6. Look at the camera’s viewfinder. If you see dark bands or a shimmering effect on the screen, your phone likely uses PWM dimming. If the screen looks perfectly uniform with no bands, it may use DC dimming (a steady current) or a very high-frequency PWM that the camera can’t detect.
7. Try different shutter speeds or frame rates. On some cameras, you can manually adjust the shutter speed or use a slow-motion mode. Slower shutter speeds (e.g., 1/60s) can make the bands more visible, while very fast shutter speeds (e.g., 1/1000s) can freeze the flicker. Experiment to get a clearer view.
8. Record a short video. Record a few seconds of the screen with the camera. Then, play the video back on a computer or another screen. You can pause the video and look for the bands frame by frame. This is especially helpful if the bands are moving fast.
9. Test at multiple brightness levels. Repeat steps 4-8 at different brightness settings (e.g., 10%, 50%, 90%). Some phones use PWM only at certain brightness levels, while others use it across the entire range. Note which levels show the effect.
10. Check if the bands disappear at high brightness. If you see bands at low brightness but not at high brightness, that’s a strong indicator of PWM dimming. Many phones switch to DC dimming at higher brightness to reduce flicker.

Common Mistakes

• Testing in a bright room: Ambient light can wash out the bands, making them invisible. Always test in a dark room.
• Using the front camera: Front cameras often have lower quality and slower frame rates, making it harder to detect PWM. Use the rear camera.
• Looking at the screen directly: You won’t see PWM with your naked eye – that’s the whole point. You must use a camera.
• Confusing screen refresh rate with PWM: The refresh rate (e.g., 60Hz, 120Hz) is how often the image updates. PWM is a separate flicker that happens at a much higher frequency (typically 200-2000Hz). The bands you see are not the refresh rate.
• Not varying brightness: If you only test at 100% brightness, you might miss PWM that only occurs at lower levels.

Tips

• Use a slow-motion camera: If your second phone has a slow-motion mode (e.g., 240fps), use it. This makes the PWM bands much more obvious and easier to see.
• Try a laptop or monitor: If you have a laptop with a webcam, you can use that instead of a second phone. Some webcams can detect PWM.
• Look for a ‘DC dimming’ setting: Some phones have a setting called ‘DC dimming’ or ‘anti-flicker’ in the display settings. If your phone has this, it likely uses PWM by default, and you can turn it off to reduce flicker.
• Check online resources: Many tech review sites and forums list PWM frequencies for popular phones. A quick search for your phone model + ‘PWM’ can give you an answer without testing.
• Use a PWM frequency app: Some apps claim to measure PWM frequency using the camera, but these are often inaccurate. The visual test is more reliable.

Troubleshooting

Problem: You don’t see any bands, but you suspect your phone uses PWM.

Solution: Try these in order:

• Lower the brightness to the minimum and test again.
• Use a different camera – some cameras have a global shutter that doesn’t capture the flicker.
• Adjust the exposure or shutter speed manually if your camera app allows it.
• Move the camera closer or further away – the bands may be more visible at certain distances.

Problem: You see bands on every phone, even ones you know use DC dimming.

Solution: This could be caused by the refresh rate of the screen, not PWM. Try increasing the shutter speed to see if the bands disappear. If they do, it’s likely the refresh rate, not PWM.

Problem: The bands are moving too fast to see clearly.

Solution: Record a video and play it back in slow motion or pause it. You can also try a camera with a higher frame rate.

Frequently Asked Questions

Is PWM dimming bad for your eyes?

Some people are sensitive to PWM flicker and may experience eye strain, headaches, or migraines. However, not everyone is affected, and many people use PWM screens without any issues. If you’re sensitive, look for phones with DC dimming or high-frequency PWM (above 1000Hz).

Can I see PWM with my naked eye?

No, PWM flicker is too fast for the human eye to see directly. That’s why the camera method is needed.

Do all OLED phones use PWM?

Most OLED phones use PWM to control brightness, but some use DC dimming, especially at higher brightness levels. It varies by manufacturer and model.

Can I reduce PWM flicker on my phone?

Some phones have a ‘DC dimming’ or ‘anti-flicker’ mode in settings. If not, you can try increasing the brightness (which often reduces PWM) or using a blue light filter app (though this doesn’t eliminate flicker).

What is a safe PWM frequency?

There’s no official standard, but many people report fewer symptoms with PWM frequencies above 1000Hz. Some phones use frequencies as low as 200Hz, which can be problematic for sensitive individuals.

Can I use a computer monitor to test my phone?

Yes, if your computer has a webcam, you can use it. Just make sure the room is dark and the screen is bright.

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