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Comment by dotancohen | Hacker News Reader

Turning down the brightness had the opposite effect for me. My monitor at the time "turned down the brightness" by reducing the duty cycle of the backlight. This caused flickering that was imperceptible yet caused much eyestrain. Actually turning up the brightness, moving the monitor as far back as possible, and using yellow-tinted Gunnar lenses have made a huge difference for me.

Edit: This is the technique used to modulate "brightness" by varying the duty cycle: http://www.waitingforfriday.com/index.php/Controlling_LED_br...

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Basically every monitor with a LED backlight controls brightness by PWM. It only causes problems if the frequency is too low. (Contrast with fluorescent lights: every single fluorescent tube in existance flickers, but only some flicker slowly enough that people can notice. https://www.youtube.com/watch?v=bjyhFyUN_zQ Ditto CRT monitors, back when they were still used. Refresh rate of 60hz is flickery and annoying, refresh rate of 72hz is totally fine.)

There's some debate about what is flicker threshold (flicker fusion threshold ,I think).

I've seen some academic literature talking about 1000-4000hz , which is far above what most screens do.

Btw I believe BenQ has a display that doesn't use pwm at all .

According to this recommendation page [0], there are quite a few monitors with "PWM-free (flicker-free) WLED backlight". The list includes many affordable mainstream choices.

I heard some monitors may revert to PWM below a certain brightness threshold, but assuming the information on that page is accurate, not getting PWM-free monitor is probably a sub-optimal purchase decision.

[0] https://pcmonitors.info/recommendations/

http://geizhals.eu/?cat=monlcd19wide&xf=103_flicker-free#xf_... lists a LOT of displays that are supposed to provide a flicker-free viewing experience, and you can also filter for other technical properties to your heart's content. (Caveat: parts of that site are machine-translated to English - but that doesn't affect the rigor that went into curating the original data).

Looks like a good resource, thanks!

Interesting observation! I actually lower the brightness to about 10-20 % on each display I use (the default settings are ultra high for a sunny day in a fully lit store) and while I have two CCFL panels (a 1000 USD 24" from the past and a 1000 USD 30") blazing at me and both of them clearly use some sort of PWM - they start buzzing audibly below 80-90 % brightness (both in their audio outputs AND even with audio disabled it is heard from the monitor itself) - there never was any visible flicker. And in the CRT days, I saw flicker up to 85 Hz (including). Color wheel DLPs are also pure hell - the image breaks into three separate colors in each eye saccade. Yet, CCFL backlight, buzzing like crazy - and no visible flicker. Enter my latest, fanciest, wide gamut screen with LED backlight - and on lower brightness, it flickers worse than a 60 Hz CRT...

However, luckily, it is not the case of each and every LED monitor - search for "flicker free" or "PWM free" - and it is not some fancy rare unicorn feature, a PWM free IPS display can cost the same or even less than flickering equivalents.

I had a Samsung Galaxy Note 10.1 2014 LTE edition and that used PWM for brightness, along with a ringing noise at certain rates.

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