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its probably not PWM

D

dopple

Gawd
Joined
Oct 5, 2011
Messages
685
PWM has been getting bad press for all the health effects people have been reporting. previously i thought it was PWM too but after using some monitors at 100% brightness and still getting eye pains the next morning and chest discomfort while using the monitor i can say it is something else.. not pwm... i can use a CRT at 85 hz and above without issue ad also my laptop (ccfl) at any brightness setting which brings in PWM. if pwm was an issue the crt flicker would also be causing issues.

my guess is it is some frequency of electro magnetic field which isnt being shielded properly or some uv radiation which isnt being shielded.

just thought id chip in for those guys who are concerned with flatscreen health hazards.

ps i have 6/6 20/20 vision.
 
It is PWM for me. I can only use displays which don't have PWM, and can't stand flickering lights.

A lot of the monitors are not PWM-free at 100%. Why I don't know. Also PWM affects LED much worse than it does CCFL, since light emission turns off immediately.
 
TotallyCool said:
It is PWM for me. I can only use displays which don't have PWM, and can't stand flickering lights.

A lot of the monitors are not PWM-free at 100%. Why I don't know. Also PWM affects LED much worse than it does CCFL, since light emission turns off immediately.
Click to expand...

so you get issues with crt also?

even i was suspecting the pwm present at 100% but out of camera range.. atleast a camphone range. any proof of this however?

yes i agree led is worse... i cant stand it at all.

by flickering lights you mean all artificial lights? because even incandescent bulbs flicker at 60hz .
 
Proof? It's common knowledge actually, but here's a camera swing test I took of a LED TV at 100%:

w1z4ep.jpg


Incandescent bulbs do flicker (and at 120Hz), but barely (they have a very weak flicker factor). They also have a pleasing spectrum. They don't bother me.

I have problems with CRT too, although I haven't used a really good, high Hz CRT in a very long time.

If it's PWM for me doesn't mean it's PWM for you, of course. I'm not telling you it has to be. You're the one who tried to "dispel the myth" that PWM causes problems at all. Many people here will swear otherwise.
 
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TotallyCool said:
You're the one who tried to "dispel the myth" that PWM causes problems at all. Many people here will swear otherwise.
Click to expand...
You are preaching to the choir. Up until now the OP has had at least a dozen threads that agree with you in one form or another.
 
dopple said:
PWM has been getting bad press for all the health effects people have been reporting. previously i thought it was PWM too but after using some monitors at 100% brightness and still getting eye pains the next morning and chest discomfort while using the monitor i can say it is something else.. not pwm... i can use a CRT at 85 hz and above without issue ad also my laptop (ccfl) at any brightness setting which brings in PWM. if pwm was an issue the crt flicker would also be causing issues.
Click to expand...
I would imagine it depends on what you do (games, static images, etc)....However, there's some interesting observations that some users of LightBoost LCD's (zero motion blur LCD's) have observed.

When playing fast-motion stuff such as video games, the lack of motion blur (CRT or LightBoost) can be less tiring on the eyes than the flicker itself (including generic PWM). That's why some people don't get eyestrain with CRT >85Hz, but gets eyestrain with PWM >=180Hz, since there's lots of motion blur on LCD displays, and trying to focus on blurred moving images during fast action video games, can be tiring to the eyes. Eliminating motion blur (thanks to the new stroboscopic backlights, allowing the CRT zero motion blur effect on LCD), makes it easier for eyes to follow motion. Although LightBoost behaves essentially like a "120Hz PWM" to the human eyes (120Hz refresh, with backlight strobes precisely synchronized to the refresh, one strobe per refresh, like CRT), users who are experienced with CRT, and trying LightBoost, report that it is no different from "120Hz CRT" to their eyes. Videogames running 120fps@120Hz, exhibit absolutely no motion blur on LightBoost LCD's ("It's like playing on my old CRT") and some users can see speed rating of 30 in PixPerAn text scrolling test.

P.S. Want to see something neat? Here's a YouTube high speed camera 480fps & 1000fps footage of a LightBoost strobe backlight -- the video shows how precisely timed strobes can clearly bypass pixel persistence as the motion blur barrier. The pixel persistence is kept in total darkness, and backlight strobes occur on fully-refreshed LCD images. Strobes can be shorter than the pixel persistence. (Modern LCD's, especially 3D-ready LCD's, now have fully refreshed frames before the next refresh cycle begins, making them compatible with strobe backlights.) Motion blur now becomes dictated by strobe length, instead of pixel persistence. Pixel persistence no longer the limiting barrier.
 
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TotallyCool said:
Proof? It's common knowledge actually, but here's a camera swing test I took of a LED TV at 100%:

w1z4ep.jpg


Incandescent bulbs do flicker (and at 120Hz), but barely (they have a very weak flicker factor). They also have a pleasing spectrum. They don't bother me.

I have problems with CRT too, although I haven't used a really good, high Hz CRT in a very long time.

If it's PWM for me doesn't mean it's PWM for you, of course. I'm not telling you it has to be. You're the one who tried to "dispel the myth" that PWM causes problems at all. Many people here will swear otherwise.
Click to expand...

that pic speaks a thousand words which monitor is that?

right incandescent bulbs work for me too. ofcourse pwm could be the issue too, but i guess it isn't an issue for me, there is something else. probably some X factor... maybe some kind of an emission elf/vlf since it makes me sick really quick just while doing simple things like web browsing. if i persist i can carry on but its pointless to persist this way.

a CRT has a lower X factor for sure. I think it meets stricter emission standards (esp the high quality 21 inchers) while LCDs in the race to go thinner and general perception of them being benign radiation wise cut corners with emission prevention, especially now non TCO displays like dell s2440l are in market.

whether this is actually elf/vlf or something else can be easily found using a regular grounded anti glare for a while and noticing the symptoms. if they go away on both lcd/crt using the anti glare screen then X=elf/vlf fields. otherwise something else.
 
Mark Rejhon said:
I would imagine it depends on what you do (games, static images, etc)....However, there's some interesting observations that some users of LightBoost LCD's (zero motion blur LCD's) have observed.

When playing fast-motion stuff such as video games, the lack of motion blur (CRT or LightBoost) can be less tiring on the eyes than the flicker itself (including generic PWM). That's why some people don't get eyestrain with CRT >85Hz, but gets eyestrain with PWM >=180Hz, since there's lots of motion blur on LCD displays, and trying to focus on blurred moving images during fast action video games, can be tiring to the eyes. Eliminating motion blur (thanks to the new stroboscopic backlights, allowing the CRT zero motion blur effect on LCD), makes it easier for eyes to follow motion. Although LightBoost behaves essentially like a "120Hz PWM" to the human eyes (120Hz refresh, with backlight strobes precisely synchronized to the refresh, one strobe per refresh, like CRT), users who are experienced with CRT, and trying LightBoost, report that it is no different from "120Hz CRT" to their eyes. Videogames running 120fps@120Hz, exhibit absolutely no motion blur on LightBoost LCD's ("It's like playing on my old CRT") and some users can see speed rating of 30 in PixPerAn text scrolling test.

P.S. Want to see something neat? Here's a YouTube high speed camera 480fps & 1000fps footage of a LightBoost strobe backlight -- the video shows how precisely timed strobes can clearly bypass pixel persistence as the motion blur barrier. The pixel persistence is kept in total darkness, and backlight strobes occur on fully-refreshed LCD images. Strobes can be shorter than the pixel persistence. (Modern LCD's, especially 3D-ready LCD's, now have fully refreshed frames before the next refresh cycle begins, making them compatible with strobe backlights.) Motion blur now becomes dictated by strobe length, instead of pixel persistence. Pixel persistence no longer the limiting barrier.
Click to expand...

thanks for putting up that video looks very cool with backlight synced with lcd refresh, quite like a CRT.

motion blur would be an issue in eye strain but the cause of the problem is more basic because even office workers/coders get this eye strain issue. motion blur is an additional factor for eye strain not the main factor.
 
PWM may be a real problem. I am so happy that I am in the camp that isn't bothered by it. Have a PB278Q running at 27 brightness :)

For me it seems PWM has been blown out of all proportions, but I realise that some people are more sensitive etc.

I remember once seeing an old 40" LCD TV, shortly after the first Sharp Aquous came out in Europe and thinking it was a smearfest because of the awful response time on the panels. I have experienced some of the bad traits that LCDs have.. but thankfully a strobing backlight doesn't seem to effect me :)
 
dopple said:
:p i didnt know i had stalkers :eek: ;)
Click to expand...
Lol, i just tend to read threads that are off the beaten path ;)


Liggywuh said:
PWM may be a real problem. I am so happy that I am in the camp that isn't bothered by it. Have a PB278Q running at 27 brightness :)

For me it seems PWM has been blown out of all proportions, but I realise that some people are more sensitive etc.
Click to expand...
Same here, i had no idea what the hubbub was about till users here described it and linked a few articles.
 
On the topic of PWM, the BlurBusters Blog is experimenting with moving camera tests. For this moving object, moving across the screen at 960 pixels per second, running at 60fps on a 60 Hz LCD:

stationarycamera-150x150.jpg


To capture the effects of PWM, if you run a 1/60sec camera exposure while sliding the camera smoothly at the same speed of a moving on-screen object, you can actually capture the image-multiplying effect of a PWM backlight. For example, this is a 180 Hz CCFL backlight, flickering 3 times per refresh. So this camera image captures 3 of the PWM pulses, so there's a triple edge effect, especially clearly seen around the yellow vertical edges.

movingcamera.jpg


This interesting edge-tripling motion blur "artifact" injected by PWM, is noticeable by the human eye on smoothly-moving high-contrast objects running at high speeds, especially if you play emulator videogames (MAME, NES, etc) on a LCD with a PWM backlight, fast sideways-scrolling platform games, or other video games that has lots of perfect 60fps panning motion running at constant speed, etc.

There's lots of interesting research on various kinds of motion blur artifacts I'm currently doing. If I had a big budget, I'd purchase a high-end pursuit camera ($$$) specially designed for measuring various motion blur. However, I'm presently investigating homemade moving-camera rigs as an expansion to my BlurBusters lab.

Thanks,
Mark Rejhon
BlurBusters.com Blog -- Eliminating Motion Blur on LCD's
 
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dopple said:
PWM has been getting bad press for all the health effects people have been reporting. previously i thought it was PWM too but after using some monitors at 100% brightness and still getting eye pains the next morning and chest discomfort while using the monitor i can say it is something else.. not pwm... i can use a CRT at 85 hz and above without issue ad also my laptop (ccfl) at any brightness setting which brings in PWM. if pwm was an issue the crt flicker would also be causing issues.
Click to expand...
Brightness at 100% has two separate problems. Either it will be too bright and therefore cause problems. Or if you reduce brightness with contrast you'll get worse problems with the various LCD shortcomings like contrast, glows, shifts, FRC flicker, motion blur etc. Although you might have tried your monitors with sunglasses or filters (which in themselves might cause some problems).

Chest pains I think would be more attributed to either new electronics fumes or tensions in the torso that would come from the effect of having eye/brain problems with the display. Both of which would lessen with time.

For me PWM is a real problem and '100% brightness with contrast dimming' actually helps even if it introduces more artifacts.
 
CrabJuice said:
Brightness at 100% has two separate problems. Either it will be too bright and therefore cause problems. Or if you reduce brightness with contrast you'll get worse problems with the various LCD shortcomings like contrast, glows, shifts, FRC flicker, motion blur etc. Although you might have tried your monitors with sunglasses or filters (which in themselves might cause some problems).

Chest pains I think would be more attributed to either new electronics fumes or tensions in the torso that would come from the effect of having eye/brain problems with the display. Both of which would lessen with time.

For me PWM is a real problem and '100% brightness with contrast dimming' actually helps even if it introduces more artifacts.
Click to expand...

does the pwm display meet TCO requirements?
 
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i was gng through some anti radiation filters and they seem to cost as much as the monitor itself in some cases.

im curious about their efficacy. do they actually block elf/vlf? are their any elf/vlfs being emitted from lcds reaching the user?

i think it is easy to measure if someone using this screen has a multimeter. using this method i could measure around 300 millivolts being drained from the ground cord to the ground in electric outlet from the 21" CRT screen. i measured a TCO compliant 22" tft and it measured 1000 millivolt. another non TCO compliant display 24" measured 1500 millivolts. interestingly i can tolerate them in their increasing order of voltage, most comfortable being the CRT.

do put in your readings if you can measure them. if you dont have a anti radiation screen, there are home made alternatives.
 
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CrabJuice said:
Chest pains I think would be more attributed to either new electronics fumes or tensions in the torso that would come from the effect of having eye/brain problems with the display. Both of which would lessen with time.

For me PWM is a real problem and '100% brightness with contrast dimming' actually helps even if it introduces more artifacts.
Click to expand...

im leaning towards electric field, just made a few measurements too.
 
I think there is problem with how you look at monitor and not PWM or radiation of any kind. CRTs are more demanding than LCD yet some people experience pain when going from CRT to LCD and vice versa. It's because brain have to learn how to use eyes properly on given monitor and the more experence it have with one type of monitor the more trouble it will have on another, especially older people can have such issues. And imho thinking that there is something wrong with monitor doesn't help at all as it introduces tension that prevent relaxation ...

ofcourse good monitor is very important so throw your W-LED crap and get NEC 2490WUXi that have identical picture from any angle so is "false 3d" free and doesn't have those abomination of an LED: White-LEDs
 
XoR said:
ofcourse good monitor is very important so throw your W-LED crap and get NEC 2490WUXi that have identical picture from any angle so is "false 3d" free and doesn't have those abomination of an LED: White-LEDs
Click to expand...

Hmmmmm...


This? (W-LED)
scw3t2.gif




Or this????? (CCFL)
yecl1.gif





Tough choice. ;)
It's only PWM that gives LED a bad rep.
 
sadbuttrue said:
I maintain blue light is the biggest issue with LED, outside of PWM. As the above chart shows, CCFL isn't immune but the spike is at least very small.

http://blogs.scientificamerican.com/solar-at-home/2011/03/21/a-better-kind-of-lightbulb/

Spectrum_CFL_LED.jpg


Spectrum_ESL.jpg
Click to expand...
Going to agree here, too much blue-light in the typical "white" LED's they are using.

Interesting studies have been posted on the effects it causes. The effects are worse, and work more quickly, than other common sources of eye strain in the past.
 
ive put in a request to tftcentral for adding info on elf/vlf/rf and magnetic fields and their strength emitted from the monitor and its power supply using a spectrum analyser in future reviews so we guys get a better idea as to WTH is causing eye strain.
 
dopple said:
ive put in a request to tftcentral for adding info on elf/vlf/rf and magnetic fields and their strength emitted from the monitor and its power supply using a spectrum analyser in future reviews so we guys get a better idea as to WTH is causing eye strain.
Click to expand...

Maybe they can also help you find Yeti. :rolleyes:

Why don't you do it yourself? Isn't there an Android app that can do some of that?
 
there is Android app for everything :rolleyes:

but those apps rarely do anything useful :(
 
TotallyCool said:
Maybe they can also help you find Yeti. :rolleyes:

Why don't you do it yourself? Isn't there an Android app that can do some of that?
Click to expand...
As a deaf guy, I can simply switch my hearing aid to the "T-coil" setting (telephone coil pickup) and I hear any magnetic fields in the audible frequency ranges -- ~50Hz-5Khz range.

But I've got a harder time hearing 1KHz-2KHz sounds, than I do with 100Hz sounds. A CRT monitor buzzes really loudly when I put my head close to the screen with a hearing aid set to the T-coil setting! So it's not an accurate relative-intensity check, as strong 2KHz magnetic fields are quieter to my ears than a weaker 120Hz magnetic field (emitting energy levels that are 20 decibels weaker).
 
Mark Rejhon said:
As a deaf guy, I can simply switch my hearing aid to the "T-coil" setting (telephone coil pickup) and I hear any magnetic fields in the audible frequency ranges -- ~50Hz-5Khz range.

But I've got a harder time hearing 1KHz-2KHz sounds, than I do with 100Hz sounds. A CRT monitor buzzes really loudly when I put my head close to the screen with a hearing aid set to the T-coil setting! So it's not an accurate relative-intensity check, as strong 2KHz magnetic fields are quieter to my ears than a weaker 120Hz magnetic field (emitting energy levels that are 20 decibels weaker).
Click to expand...

thats incredible how does the LCD sound to you? one with ccfl and one with led?
 
dopple said:
thats incredible how does the LCD sound to you? one with ccfl and one with led?
Click to expand...
LED is much quieter. The CCFL in a Samsung 245BW sounds like it has a 180Hz hum, which is normal as my hearing aid T-coil, designed to pick up fields from speaker windings in a telephone, also picks up the buzz of 180Hz. However, even the 180Hz buzz is much quieter than the 60Hz buzz of a CRT. The EMI (Electromagnetic Interference) of displays has been steadily going down for many years, and is almost negligible for many LCD's.

This is to be expected, LED doesn't require much voltage, and the lower power levels of LED, and the high efficiencies of switching transformers these days, don't seem emit enough interference for my hearing aid to pick up in newer monitors. Some monitors are silent and some have a noticeable buzz.

Those people complaining they hear a faint squeal or hum from their monitor? You know, sometimes the tiny transformer found in some switching power supplies, sometimes themselves acts like a speaker (vibrates at the switched frequency) -- and actually produce an audible buzz equal to the frequency of the switching. The T-coil sounds exactly the same as that, but much, much, much louder. So those switching transformers that faintly buzz, has a very terribly loud buzz with my T-coil. Some cheap PWM circuits do make a buzz, but not nearly as badly as CCFL did, which in itself didn't do it nearly as badly as CRT. The buzz mainly comes from the power supply nowadays.

Thankfully, I don't use the T-coil setting while I sit in front of computer monitors. But lately, I hear silence from most good LED monitors. Low voltages, low power levels (many now use only 20 watts), high efficiencies. I'd say most LED monitors have quite negligible EMF emissions. Easy to see that your health hazards will mainly be your eyestrain (picture issues, PWM, etc) and whatever plasticky-smelling outgassing comes from a new monitor.

From my T-coil buzz detection, I get far more EMI standing next to a lamp or even next to certain parts of a wall (electric wires inside wall) -- I hear the 60Hz hum from those when I stand close enough with the T-coil. Also, lately, the power supply for a monitor is sometimes separate from the monitor itself -- a monitor power brick emits far more EMI than the monitor itself does. Quite a loud buzz when I put my hearing aid T-coil against a power brick.

In one apartment I used to live in, I had a bed against the wall that the building's 200amp electrical power supply was running up along on the opposite side of the wall, into the house. THAT 60Hz buzz was insanely loud with my hearing aid's T-coil (it clipped against my hearing aid's maximum sound volume!!). During high-power-consumption days, the field was also strong enough to shift the needle of a compass, too -- several feet away, IIRC. I sometimes wondered what the strong magnetic field was doing to my brain while I was sleeping. (knock on wood!)

It's amazing how much magnetic fields a hearing aid's T-coil picks up.
 
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Mark Rejhon said:
I'd say most LED monitors have quite negligible EMF emissions. Easy to see that your health hazards will mainly be your eyestrain (picture issues, PWM, etc) and whatever plasticky-smelling outgassing comes from a new monitor.

From my T-coil buzz detection, I get far more EMI standing next to a lamp or even next to certain parts of a wall (electric wires inside wall) -- I hear the 60Hz hum from those when I stand close enough with the T-coil. Also, lately, the power supply for a monitor is sometimes separate from the monitor itself -- a monitor power brick emits far more EMI than the monitor itself does. Quite a loud buzz when I put my hearing aid T-coil against a power brick.

In one apartment I used to live in, I had a bed against the wall that the building's 200amp electrical power supply was running up along on the opposite side of the wall, into the house. THAT 60Hz buzz was insanely loud with my hearing aid's T-coil (it clipped against my hearing aid's maximum sound volume!!). During high-power-consumption days, the field was also strong enough to shift the needle of a compass, too -- several feet away, IIRC. I sometimes wondered what the strong magnetic field was doing to my brain while I was sleeping. (knock on wood!)

It's amazing how much magnetic fields a hearing aid's T-coil picks up.
Click to expand...

what led monitors do you recommend being the quitest in led based on what you hear?
some monitors have a built in power supply how do they sound?

so when you pick fields from wiring those wiring are in metal pipes inside the walls or in plastic piping? does metal pipe reduce the sound you hear?

i imaging you couldnt sleep in such a bed where 200 amps was going if yo could hear it, are the wires in walls loud enough to disrupt your sleep if you were hypothetically sleeping with t-coil setting?

very interesting ability you have! :D
 
dopple said:
what led monitors do you recommend being the quitest in led based on what you hear?
some monitors have a built in power supply how do they sound?
so when you pick fields from wiring those wiring are in metal pipes inside the walls or in plastic piping? does metal pipe reduce the sound you hear?
Click to expand...
As for LED's, my T-coil no longer picks them up anymore at 2 feet distance. I have to press my ear against the monitor to hear anything now -- even when the power brick is built into the display.

As for the power wiring and the T-coil detection, I don't know, but I think it was just thick black cable coming from the power pole, as it was very near the circuit breakers that was in the room right below me. That was more than 10 years ago.

i imaging you couldnt sleep in such a bed where 200 amps was going if yo could hear it, are the wires in walls loud enough to disrupt your sleep if you were hypothetically sleeping with t-coil setting?
Click to expand...
I never wear my hearing aids to bed -- that's one good thing about being deaf -- my ears essentially have an "OFF" switch. :D

We're getting off topic now, so on that note -- let's talk PWM.
 
Mark Rejhon said:
We're getting off topic now, so on that note -- let's talk PWM.
Click to expand...

right coming back to the topic i wonder how important a-tw polariser is for proper binocular cues esp when coupled with bright blue flickering backlight.

maybe nec2490wuxi users get little to no eye strain.
 
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