Slashdot Mirror

It still good to ponder what flicker could tell us. For example, the 200 Hz LCD backlight PWM frequency causes sore eyes and headaches to many people, so certainly the eyes and/or nervous system are sensing something? Put some white text on a black background on a computer like that and you can see multiple images of the text when rapidly turning eyes horizontally. Of course, as you say, the picture appearing and disappearing is largely a different discussion when compared to motion sensing, but there might be a bridge which can combine these discussions for some benefit.

Then you want to look at the Asus PG278Q 1440p monitor or imaginatively named PB287Q 4k monitor

For those people who don't mind CRT's, but get eyestrain from motion blur instead, there's a new technology called LightBoost (google "LightBoost") which is essentially PWM at one strobe per refresh, with 92% less motion blur than regular 60Hz LCD (full order of magnitude less motion blur).

Competition gamers have been purchasing 120Hz computer monitors as of late, and enabling the LightBoost strobe backlight, to regain CRT like clarity; covered at the Blur Busters Blog - http://www.blurbusters.com/ -- which also has 60Hz versus 120Hz versus LightBoost comparisions available.

And TFTCentral's "Motion Blur Reduction Backlights Including LightBoost":
http://www.tftcentral.co.uk/articles/motion_blur.htm
They found that LightBoost greatly outperformed scanning backlights.

Obviously, this technology is not for flicker sensitive people, but it can be turned on/off, and it's another option on the market.

The best implementation is called LightBoost -- PWM at one strobe flash per refresh, for the CRT effect
http://www.blurbusters.com/faq/60vs120vslb (60Hz versus 120Hz versus LightBoost).

Also TFTCentral's "Motion Blur Reduction Backlights Including LightBoost" article:
http://www.tftcentral.co.uk/articles/motion_blur.htm

They also have a dedicated page with an overview to the topic.

"The old CRT refresh rates were mitigated by having phosphors"

The LEDs used for backlights have phosphors as well. They obviously don't have the same persistence as the phosphors on CRTs, but they're still there.

Some monitors deliberately cause the backlight to flicker in time with the screen refresh rate, as some people find this to lead to clearer vision, less eye strain and less motion sickness. I don't think this is very common though.

Related info: http://www.tftcentral.co.uk/articles/pulse_width_modulation.htm

Benq is in the process of introducing non-PWM flicker free backlight LED monitors.

http://www.tftcentral.co.uk/news_archive/28.htm#benq_bl2710pt

Does reviews that include assessments of PWM in monitors. Very recommended.

http://www.tftcentral.co.uk/

Read the reviews about PWM LED systems and take it into consideration.
http://www.tftcentral.co.uk/articles/pulse_width_modulation.htm
Go for top end Dell, the ~$1000 Eizo range.
Any Australian tech forum has a post on the Korean IPS options:
"27/30" Korean Monitor Guide/Help Pt2"
http://forums.whirlpool.net.au/forum-replies.cfm?t=2023067

I just bought a laptop online. It looked great on paper, had a great keyboard, and within 10 minutes it was driving me crazy. I hadn't bought a laptop since LED backlighting took over, and it turns out that there's now Yet Another Hidden Specification you have to check for.

Most manufacturers (not Apple) use pulse-width modulation (PWM) to control the backlight brightness. When you set the brightness to less than 100%, the backlight LEDs will be pulsing at some fixed frequency (perhaps 200-700 Hz) and a duty cycle determined by your brightness setting. (Some laptops may pulse the backlight even at 100% brightness, depending on the backlight LEDs.)

The problem is the laptops with a PWM frequency closer to 200 Hz than 700. This is above your eye's flicker-fusion threshold, so if you're staring directly at the screen you won't see any blinking. But when your eyes are moving over text, instead of getting a nice clean motion blur, they'll get a few distinct copies of the letters. This makes the screen look blurry in a weird indefinable way that can drive you crazy. (It gives me headaches.) At higher PWM frequencies, your eye sees something closer to a true motion blur, and the problem decreases.

The problem is much worse with LED backlights than CCFLs, because the CCFLs respond more slowly to the PWM pulses, so the brightness ramps up and down more evenly. LEDs respond quickly, producing clean, sharp pulses.

Unfortunately, no manufacturer seems to list the backlight PWM frequency in their specifications. Luckily, it's not too difficult to test if you have the laptop in front of you. Go to a store and look at the demo laptops. Bring up a mostly-white screen (e.g. a web browser displaying about:blank), then turn down the backlight to 50%. Wave your hand back and forth in front of the screen as fast as you can. You probably won't see a nice clean motion blur unless you're looking at a Mac. Instead you'll see many distinct outlines of your fingers. If you see a lot of outlines, spaced close together, the backlight is decent. If you see a few, spaced far apart, beware! I tried this earlier this week at my local Best Buy, and only a few laptops had a PWM frequency higher than the one that was giving me headaches.

This article explains the problem in more detail, including instructions for using a digital camera to find the actual PWM frequency of your monitor.

Better colour gamut, no flicker, always perfectly sharp, no distortion, etc...

The adjustable brightness of LCD displays is normally implemented using pulse width modulation that can cause visible flicker. This is apparently much more visible with LED backlights than with the CCFL backlights.

Flicker from LED backlights is typically much more visible than for CCFL backlights at the same duty cycle because the LED's are able to switch on and off much faster, and do not continue to "glow" after the power is cut off. This means that where the CCFL backlight showed rather smooth luminance variation, the LED version shows sharper transitions between on and off states. This is why more recently the subject of PWM has cropped up online and in reviews, since more and more displays are moving to W-LED backlighting units now.

@see Pulse Width Modulation

I think it's worth the $400. I'm considering getting another one this year, assuming nobody comes out with a larger standard-gamut matte display.

As far as response time, I don't game, but I've not had any problem watching fast-action movies. The most in-depth review you're likely to find can be found here: http://www.tftcentral.co.uk/reviews/content/hp_zr24w.htm

Haha, that is way in-depth. I'll probably get that screen. Cheers man.

I think it's worth the $400. I'm considering getting another one this year, assuming nobody comes out with a larger standard-gamut matte display.

As far as response time, I don't game, but I've not had any problem watching fast-action movies. The most in-depth review you're likely to find can be found here: http://www.tftcentral.co.uk/reviews/content/hp_zr24w.htm

I'm thinking about getting HP ZR24W, it's a quality screen with 1920x1200. At least it won't be a setback from 1600x1200.

http://www.tftcentral.co.uk/reviews/hp_zr24w.htm

http://www.tftcentral.co.uk/ Great site and they even tell you if the panels are TN or not.

for photography you don't want the sort of screen they have on a laptop..... not unless there are any laptops with PVA or sIPS panels out there...

That's why I'm looking for a big external monitor for editing. A laptop display can be used on site to browse photos and see which ones are good and which aren't. The graphics card in my MacBook Pro can drive a larger 1920 X 1200, or whatever, monitor. New MBPs can drive bigger, higher resolution monitors. As for panel techs, while M/PVAs may be good for games they aren't for photography or graphic design, though they are better than the TN panels laptops come with. Using an external monitor though the laptop display can be used to hold all the pallets and tools for when editing a photo on the external monitor. Oh, about S-IPS panels, H-IPS are better. If I could find a local store that carried one I'd like to look at the HP LP2475W which has an H-IPS panel. But it doesn't have an internal LUT, Look-up table. Otherwise you're looking at Eizo, LaCie, or NEC monitors which cost above $1000.

Falcon

Despite the GP's warning, I've just recently purchased a Dell 2408WFP (a couple generations/revisions newer than the 2405WFP) and I couldn't be happier. It's a 24" P-VA panel with 1920x1200 resolution.

The color quality is fantastic, especially compared to my previous (good quality) 19" LG TN panel. The response time is perfectly good and I haven't noticed anything resembling lag regardless of what types of games I've tried.

The viewing angle isn't as good as an IPS panel, but it is far superior to a TN. Also, even when the colors change as your angle changes, the difference isn't as dramatic as with a TN panel.

As far as extras, it's got a handy 4-port USB hub built in, along with memory card reader slots (one for SD/MMC/MStick and one for CF). It also has many connectors on the back: VGA, 2 DVI, HDMI, DisplayPort, composite, component, and S-video.

The nice thing about all the connectors is that you can use it as a TV display if so inclined. There's no tuner, but it would be great for a DVR output. It also has two built in speakers, however I've not used them and I've read that they sound awful (which isn't at all surprising).

These two reviews gave me a lot of information before I bought the panel:
http://www.tftcentral.co.uk/reviews/dell_2408wfp.htm
http://monitortest.blogspot.com/

I have the 2407 WFP (the pre-HC, they released the wider color gamut HC model two months later). Best monitor I have ever used.

I just tried one of the test images from http://www.tftcentral.co.uk/articles/6bit_8bit.htm on
a year-old Macbook, and the smooth gradients looked equally ugly in OSX and in WinXP running under Parallels. I couldn't see any difference running XP in a window or running it full screen. So I suspect the claim that XP is better is just BS.

I don't guess based on the spec sheet, which often tells you precisely nothing. Instead I find out what the panel is by looking it up on sites like this one:

• http://www.tftcentral.co.uk/panelsearch.htm

You can read about the different kinds of panel on wikipedia:

• http://en.wikipedia.org/wiki/TFT_LCD