Eye strain when looking at displays? PWM explained

Lots of us have experienced eye strain and headaches after looking at certain displays for some time.. But have you wondered why? IMPORTANT! As stated by user vaddimka, you can check devices on external sites such as 'rtrings' and 'notebookcheck' and find test results for said devices on whether PWM is noticeable and how much it actually is - thus helping you decide your future purchase. Video Timetable 0:00 PWM 0:35 How does it work? 01:05 Pupillary Light Reflex 01:50 PWM Screen Examples 03:00 Reduce PWM