Is This PWM, Dithering or something else?

wlmsn

I was looking at a Chromebook CX34 at Target the other day because I need a computer to do some writing on. It's IPS so I thought it would be ok with PWM.

Within 3 minutes I had a headache and some nausea that lasted most of the day. I noticed that the words were fuzzy and flickery, which is probably the reason for the nausea.

I took a video with my camera in slow motion to show what it looks like - https://youtu.be/XpvgoVFZ0dk. Notice that part of the letters flicker from back to fuzzy white. When I do it on my Macbook Pro 2011 the letters remain crisp and clear no matter how slow the video is.

Is this PWM, Dithering or something else? Trying to get a handle on what the actual problem is here.

(Sorry for the shaky video)

KM

It is difficult to see the problem, with the video being low resolution (144p) and the camera moving. I see some white pixels on the letters, but it's not detailed enough. The cause of the symptoms is most likely some sort of flicker, as I experience myself that headaches and nausea can kick in fast when exposed to certain kinds of flicker, but we need more sophisticated measurement methods. I have experienced such symptoms both with backlight flicker (e.g. PWM) and by plugging in a specific graphics card. So I know the symptoms indeed can be caused by both PWM and pixel flicker.

wlmsn

KM yea I see what you mean.

I'm not sure this is any easier to see but here's the uncropped version - https://youtu.be/18o1o5ClKAE

GregAtkinson

The best way to figure out if it's PWM is to build the oscilloscope/light detector that @KM described here: https://ledstrain.org/d/312-homemade-oscilloscope-to-detect-pwm-diy-guide/42

I built it a couple years ago and it has been extremely helpful. I found it dauting at first but totally worth it.

There's a commercial version of the light detector (but you still need the oscilloscope) that you can buy for a couple hundred bucks, if you'd rather spend money than time. I have not bought it myself, but I believe Notebookcheck uses it.