http://en.wikipedia.org/wiki/Frame_rate#Background

At 200hz, it's on for 2.5mS and off for 2.5mS. I cannot agree with your analysis, because the human eye is not fast enough. Period.
That doesn't matter; you still get your headaches, but you are pretty much alone in ascribing them to the background flicker. I would urge you to work with every other aspect of your picture. Everything, including the amount of background lighting that is perceptible affects the vision.

Don't be so quick to dismiss the issue. There's many people who get sore eyes or headache from the typical 200Hz backlight frequency. The Wikipedia frame rate article you are referring to refers more to sensing fluid motion in animation. But when a LED backlight is pulsed fully on and off (and LED does not have any reminiscence, like CCFL did), you really need multi-kHz signal to be completely comfortable.

I can easily even see double images of things on the screen. Turn the brightness quite down and place a white mouse cursor on black screen while moving your eyes left and right, this should demonstrate it.

The BenQ flicker-free series of desktop monitors are excellent, as they limit the LED current instead of doing PWM. I wish we can see something like that with laptops too.

What's the frame rate when you're watching? would not that be a bigger cause of flicker?

It would not because the liquid crystals of a display change their state smoothly and there is no black image between.

What's the frame rate? That's what solves other people's problems. You do realize that dimming is enough to produce flicker, and if there's no black state as you suggest, it undercuts your complaint about backlights.

I am going to leave you with the last word on this, because I'm not helping you.

Relax, I am not asking help. But yeah, the frame rate of LCDs is pretty much always 60 fps and I do not have any complaints about that. However the backlight PWM is still controlled separately to the picture signal.

psy__, oscilloscope is a very expensive thing, so do you have possibility to test with your oscilloscope if some Lenovo ThinkPad T440s with HD+ display is also flicker-free? I want to buy this laptop, but I don't have an oscilloscope, and Lenovo ThinkPad T440s with FHD display is also too expensive for me.

Way past your interest in this thread, I suppose. Have you seen this?
https://wiki.archlinux.org/index.php/backlight#brightd

Don't mind the https - I have some always-https plugin. Some tools seem to offer control of backlight flashing frequency on intel stuff. YMMV.

This is true, if one is running Linux and Intel HD Graphics, the backlight frequency can be changed through writing into a certain register.

From a hardware-messing point of view: Wouldn't it be easy to just add a capacitor in parallel to the backlight LED? (This is assuming that the LED has a proper series resistor to limit the power intake.) That way by PWMing the backlight you'd actually be supplying an near-constant voltage which should almost eliminate the flickering (and also the headache).
(I don't have this backlight flickering problem but depending on how tired I am I can see any flourescent tube flicker in the corner of my eye, so this problem sounds very reasonable to me.)

I experienced the same flicker issues with led monitors . Took some time to realize the cause as LED backlit and now experimenting with benq flicker free monitors. In search of a model in laptops which implements a flicker free technlogy or a laptop which still uses ccfl backlit, as the new laptops are with LED backlit thus making it difficult to find one.

has list of PWM free laptops

http://laptopmedia.com/top-laptop-pw...t-on-eyesight/

has list of PWM free laptops

Cool. If you become aware of something similar for desktop displays, it will be much appreciated.

I just tested my Lenovo X1 Carbon 3rd gen with the 1080p non-touch display running OpenSUSE Tumbleweed. Including "off" and "max", there are 11 brightness settings (0-10 for future reference in this post). Only the bottom two settings (1 and 2) use PWM control, with #1 being 50% DC and #2 being 90% DC, both at 220 Hz. All other levels 3-10 use linear control. It does use the Intel chipset, so I attempted to change the PWM frequency to 1 kHz, but unfortunately it changed the entire brightness scale. #1 went to 1 kHz 50% PWM, but #2-10 went to full power, so I effectively just went from 11 brightness settings to 3. I'm not sure why that is, but either way I never use brightness settings 1 or 2 anyway since they're too dim, so I'm always in the linear range regardless.