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Can PWM be removed from LED LCDs?

Last response: in Computer Peripherals
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March 23, 2011 6:24:04 PM

Hello,

Can someone help me figure out if this is possible? I wasn't sure where to put this question. I hope I'm right here.

I am strongly convinced that the backlight modulation by the PWM of LCDs is having a bad effect on my health (I don't want do go into detail). Therefore, I'd like to know if it is possible to remove the PWM from an LED backlit LCD physically and have no subliminal flicker and the monitor still working afterwards.

I have heard that some LEDs disable the PWM automaticly at a full brightness setting but I don't want to risk buying one that would flicker at full brightness. I am aware that the LCD would loose its dimming abilities, be brighter, consume more electricity, have a shorter lifetime etc. The only thing that matters to me is to have the flicker removed and the display showing a picture after the removal of the PWM. By flicker I mean every form of it that is visible or invisible to man.

Whould people that repair electronic devices such as monitors be able to remove the PWM and connect the LEDs where the PWM was previously connected? Or would they not know what a PWM is? I'm not planning on doing this myself.

Is there only one PWM that needs to be disabled or disconnected are are there loads of them in LED backlit LCDs? I am not interested in doing this with CCFLs.

Thank you for any helpful answers. It would really mean a lot to me if this was possible.

More about : pwm removed led lcds

March 23, 2011 6:49:11 PM

I don't tinker with monitor internals, but I have a question for you to think about before you go through with it:
Are you sure viewing the screen at full brightness won't have worse effects on your health? LaCie recommends 120 cd/m2 for lcd monitors, but most LED-backlit monitors offer 200-300 cd/m2 at max brightness.
March 23, 2011 7:12:53 PM

I will find other ways to dim it. That's not a problem.
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March 23, 2011 8:49:29 PM

Generally speaking PWM is disabled at full brightness because PWM is used to lower brightness.

If you believe you are susceptible to flickering issues, then the dimmer you set the brightness to the more PWM there will be. Therefore, setting it to full brightness is better for you. However, full brightness generally cause eye fatigue so you are trading in one issue for another.

I would recommend looking into a screen for your monitor. Kinda like a security screen so that the person next to you cannot read what is on the screen. This type of screen is a polarization screen (not sure if that's the exact name) since it uses a polarized screen to block some of the light from passing thru.
March 24, 2011 8:42:21 AM

Getting such a screen was my intention, besides darkening the pixels a bit thrugh other settings. The problem is that I have read on other forums that people had measured some laptops with LED screens (don't remember the forums or LEDs) and some continued using PWM even at full brightness. The explanation is that manufacturers are using PWM at full brightness to improve apprent response times or the LEDs are too bright at full brightness to be safe so they dim them. They always seem to find a reason to use PWM.
March 24, 2011 10:25:33 AM

OP,

if you do a forum search you might be able to find an few posts by someone on here claiming to have an issue with current CCFL & LED backlights . if i remember correctly he changed the backlighting to incandescent which eliminated the problem (for him). he mentioned something about flicker (which i assume to be a pwm reference)
September 9, 2012 9:11:43 AM

I have come to believe that measurements others made are not 100% reliable, because I have come across a case where 2 measurements of the same LCD had different results.
January 4, 2013 8:53:45 AM

Recently bought ViewSonic VP2365-LED - it is total crap. Flickering is so strong... it is flickering like old cheap CRT! It is flickering on all brightness settings, and on ECO mode. I bought it supposing ECO mode would just disable set of LEDs so it would not flicker... but it was wrong! My old Nec1970NX is much, much better!

There is definite need to have way to fix it.. either manually or by software.
Anonymous
February 10, 2013 11:50:31 PM

Every LCD monitor will have an 'LED Driver unit' powering the LED backlight. These are normally PWM controlled because that method gives greater uniformity in dimming and colour, and is cheaper to but means flicker. :ouch: 

The alternative is a constant-current driver = no flicker.

I'm looking into this at the moment, but there should be some way of replacing the PWM driver with a CC driver in an LCD monitor.

Monitor flickering is a big ANNOYANCE! :ouch: 
June 4, 2013 11:09:03 AM

Today I have removed myself PWM brightness control from new TV/monitor AKAI 32' AKFL3274HF3 on CCFL bulbs . It have: 32' LG 1920x1080 with passive LG 3D with no visible input lag and good viewing angles. (TN, IPS ?). I don't recognized disturbing flicker in most tests from: http://www.lagom.nl/lcd-test/.

In comparision to 24' ACER G245h which was comfortable to my eyes: 2 CCFL edge monted bulbs with no PWM flicker by turned on 100% brightness, AKAI has: unknown number of CCFL bulbs behind screen and constant (smaller or lower) PWM flicker on all settings. Any colour shifting, brightness and even many good eyeglasses + window with three glasses before screen failed to protect against eye fatigue and pain in the right eye.

Before removing PWM camera showed flicker even with 100% backlight. It looked like noise.

So I opened the TV and disconnected only brightness control wire from main board to backlight inwerter build on OZ9966SN chip. That's it. I can post more info about it. (Next step will be analog dimming by reducing the CCFL lamp current to and to save energy from 160 Watt to 65 Watt.)

There is no brightness control now, but dimming by monitor contrast has very wide level. A screen finally is super stable. Camera shows nothing like in ACER monitor.

I can't say how this will work for my eyes now, becouse I have a pain from yesterday day. So removing PWM from CCFL/LED monitors and TV could be very easy.

PM. So far so good, I don't feel tired eyes problem from a few hours.
July 15, 2013 2:36:52 PM

Removing PWM was not sufficient. However my eyes was not tired any more, but I still felt the burning eyes. So second step was turning on analog dimming on OZ9966SN. ADIM had 5 Volt on his leg and was connected with VREF leg (but analog driving is in 0,5 V - 2,5 V interval). So I short this leg by 1kOhm resistor to ground. With less then 0,1 V on this leg, driver chip dimmed lamps by changing it's electrical current to minimal. CCFL and EEFL could be dimmed by analog only 2,5 times with current.

Effect: before with 100% backlight turned on and 100% contrast LCD panel shined like a sun. After dimming you can look at without fear of blindness. TV/monitor is cold now. But my eyes was still in pain. Not such severe but still.

Then I added 3 cm PMMA Perspex 133 Ivory colour (with UV blocker) inside LCD panel before diffuser (dffuser must stay inside panel becouse it has different light diffusiun and your eyes could hurt) which is blocking all blue spectrum of EEFL. Now after longer tests I see that it works. (Normal yellow thinted glasses or yellow ski googles was transitted some blue thus not working for me with that screen) After hours of work no more eyes burning.

The spectra of some fluorescent and LED are too high in blue, so without proper protection are eyes will suffer now or later.
August 22, 2013 11:08:00 AM

I don't know if this will help you, but it has for me. I have a T430 thinkpad that does this. I have to have my screen at full brightness but I use a a dimming utility for windows called "Dimmer". I also use flux to keep the eye fatigue down.

The downside is that my battery life sucks when taking it out. I wish that someone could find a solution to stop the pwm from hurting my eyes and getting a major headache
!