Is the flicker-free technology really good for our eyes?

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Apr 3, 2014
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I saw the description of BenQ VW2245:“The Flicker-free technology eliminates flickering at all brightness levels and effectively reducing eye fatigue. ” Is this technology really better for our eyes? If it is, why?


PS: Thank you for all your replies!

Thanks to poindexter tell me this: Turn Your Kindle into a Second Monitor. http://lifehacker.com/5928912/turn-your-kindle-into-a-second-monitor
E-ink is my favorite screen.
I hope it will be a common specification in the coming future. :)
 
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teh_chem

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Personally, I don't think flicker free tech has a significant impact on eye strain. Your eyes will still be focusing a lot on things on the screen; flicker, as is appears on current monitors, doesn't change that.
 

Mr.Pixel

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The reason backlight flickering is used at all is one of manufacturing convenience. It is very simple to produce a dimmable light source by rapidly turning it on and off, though doing it well is another matter. Flicker-free technology is not new, it just means they took the time to design a proper electrical circuit.

Can you name a natural source of flickering light? If humans have dealt with only constant illumination until the introduction of electric lights, shouldn't the question really be: Is flickering technology bad for our eyes?

Personally, a non-flickering display means the difference between no headaches, VS almost daily headaches with a flickering one. This is not true of all people, but does appear to be the case for a subset.
 

Bluesun311

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If you have a smartphone just take video of the monitor and it'l be real obvious if there is flicker. Appears as lines across the display. PWM free displays will show clear on video. A portable fan in front of the monitor will make it visible to your eyes as well. Flicker is probably not a cause for great concern as humans used CRTs for years and they flicker, but not in the same way that LCD monitors generally do. Some LCDs are clearly easier on the eyes than others. At the same time, some people are far more prone to eye-strain than others.
 

teh_chem

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Making a video of the monitor to see that 'flicker' is only showing you the difference between the monitor refresh rate and the camera's capture speed. That's not the 'flicker' that they're talking about. Flicker from display illumination/dimming is not monitor refresh rate. You'll always see refresh rate asynchronicity if you record it, of course assuming the framerate of the recording is not matched in time and speed to the refresh rate of the display.
 

Bluesun311

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Making a video of the monitor to see that 'flicker' is only showing you the difference between the monitor refresh rate and the camera's capture speed. That's not the 'flicker' that they're talking about. Flicker from display illumination/dimming is not monitor refresh rate. You'll always see refresh rate asynchronicity if you record it, of course assuming the framerate of the recording is not matched in time and speed to the refresh rate of the display.

Hmm, I tried it on this fg2421 by turning the brightness to zero and it didn't seem to work, still looks clear on video, but I know it's supposed to have PWM at lower brightness. LCDs have seemed to me for a while not to do this ugly CRT lines across the screen on video effect. In my defense, I was just going off what Benq states in their video about flicker-free displays... I should have known better.

I give this post my BlueNewb seal of approval for disproving a myth I was perpetuating, apparently. :D
 

StoleMyOwnCar

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Can you name a natural source of flickering light? If humans have dealt with only constant illumination until the introduction of electric lights, shouldn't the question really be: Is flickering technology bad for our eyes?

... Candles? Campfires in windy-ish weather? That's a really bad question, because that's all that we used to have before electricity. Hell flickering (the word) was practically made for candles.

The better question is rapidly (ie very rapidly) changing light. CCFL pose as much of an issue when PWM dimmed as LED's for the simple reason that its light wave form isn't a straight drop after it's turned off, but a slope. Now LED PWM I can see as being very unnatural.
 

NCX

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The FG2421 uses an extremely high PWM Frequency (18khz?) when set below 20% brightness. Most monitors which use PWM use low 130-360hz frequencies (LG & Samsung like to use 130-180hz, even in their high end, 700-1000$ monitors!) which shows up on camera. I'm not sure how high the frequency needs to be to not show up on camera.

BenQ Flicker Free Video.

Read about LED PWM Dimming Side Effects
.
 

Comixbooks

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Being I have sensitive eyes brightness affects me more then anything.......
 

Mr.Pixel

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... Candles? Campfires in windy-ish weather? That's a really bad question, because that's all that we used to have before electricity. Hell flickering (the word) was practically made for candles.

Actually, I was thinking of the fact that probably >99% of all photons you'll ever see come from sunlight (which obviously does not flicker).

The better question is rapidly (ie very rapidly) changing light. CCFL pose as much of an issue when PWM dimmed as LED's for the simple reason that its light wave form isn't a straight drop after it's turned off, but a slope. Now LED PWM I can see as being very unnatural.

Yes, I should have specified rapid flickering. One of the largest factors in perceiving flicker is not the shape of the pulse waveforms, but their modulation (how far the light turns off during each cycle). For example, incandescent bulbs flicker at 120Hz (in the US), but the modulation is <10% so the flicker is not objectionable. Both CCFL and LED backlights can be objectionable if they are driven such that their modulation is 100%, and this is easier to do with LED. The shape of the curve itself doesn't matter so much once the rate becomes fast enough.

I'm not sure how high the frequency needs to be to not show up on camera.

The effect you see in video is a form of temporal aliasing due to interference between the flicker rate and the video fps. There's not really an easy way to predict what the interference patterns produced will be without prior knowledge of both, and that becomes only more confusing with the effect of rolling shutter.
 

CrabJuice

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Weird phrasing for the thread title. PWM free monitors are certainly not worse for your eyes. Monitors that do flicker might be bad for you. On the other hand there is lightboost, where flicker might be advantageous.

The main technical reason for using PWM is that there is a certain gamut shift when dimming with current control. Something which might matter to professional graphics people, photogs and such. Thats why you see some models with very high frequency cycle or pwm dimming at lower brightness levels, in an attempt to solve both problems. Although very high frequency has its own set of problems such as EMI.

There is plenty of flickering in nature. Although its never that harsh. The main problem with PWM dimming is when you want to have low brightness then on cycle time becomes very short and relatively very high. Not natural at all. This is what screws some people over royally.
 

AgentQ

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OK, so how do we identify a non-flickering display?

Before purchasing: Diligently comb through reviews and threads online.

If you've already purchased and it doesn't bother you, then it's not a problem. The better for your eyes angle is probably an artifact of the marketing department translating info from the R&D department.

On the other hand, if you do find yourself noticing a subtle flickering or developing headaches and eyestrain from your monitor, it might be worth looking elsewhere. The placebo effect is very strong, so it's worth at least verifying that your monitor has a low PWM frequency before you blame it for your eyestrain woes.

PWM isn't inherently bad. In fact, properly executed PWM leads to much better color uniformity across brightness settings. The problem comes when the PWM frequency is too low to let your visual system properly integrate the pulsing brightness into a perceived uniform brightness level. This is most evident at lower brightness settings, when the on-time of the backlight becomes very short, leaving relatively large gaps between light pulses.

My boss once bought a bunch of super cheap monitors for the office with horrible PWM flicker. Some people didn't notice it, but others (myself included) were being driven crazy by it. It definitely varies from person to person. The only solution I could come up with was to run the monitor near 100% brightness, which essentially took PWM out of the equation. Of course, too high brightness is going to cause eye strain as well, so I spent a bunch of time swapping lightbulbs in the room with 100W CFLs from the supply closet to bring the ambient light level up to match. Would have been much easier to just buy everyone decent monitors to begin with. :rolleyes:
 

AgentQ

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Weird phrasing for the thread title. PWM free monitors are certainly not worse for your eyes. Monitors that do flicker might be bad for you. On the other hand there is lightboost, where flicker might be advantageous.

The main technical reason for using PWM is that there is a certain gamut shift when dimming with current control. Something which might matter to professional graphics people, photogs and such. Thats why you see some models with very high frequency cycle or pwm dimming at lower brightness levels, in an attempt to solve both problems. Although very high frequency has its own set of problems such as EMI.

Great explanation. It should be noted that the EMI problem isn't a problem for the end user (us). It's really just a problem for the engineers who have to get the product to pass all of the required EMI testing to meet regulations. :p

Companies love to use lower PWM frequencies because it's much easier to get the monitor to pass EMI testing, at the expense of decreased performance. Higher quality monitors tend to have larger EMI compatibility budgets, so they're willing to spend the extra time and money to get the higher PWM frequency passing EMI tests.
 
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Nice discussion! Thank you guys!
My favorite screen is Kindle paperwhite. Is it possible to use e-ink display as a monitor?
 
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Apr 3, 2014
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that's really cool!!
however, it's too difficult for me to jailbreak my kindle. :(
i hope amazon will have a plan to develop an e-ink monitor. i will definitely buy one ( if the price is acceptable. :p )
 

sadbuttrue

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PWM is bad regardless of the frequency. Even if you hit 1,000,000hz you're still subjecting the nervous system to a barrage of instant on/off pulses of light. Sure you will no longer get eyestrain or headaches, but the underlying effects will be there building up over time.
 

teh_chem

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PWM is bad regardless of the frequency. Even if you hit 1,000,000hz you're still subjecting the nervous system to a barrage of instant on/off pulses of light. Sure you will no longer get eyestrain or headaches, but the underlying effects will be there building up over time.
Such as?
 
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