Re: Headache, bad for eyes LCD displays

"Steve Reeves" <steve@xxxxxxxxxxxxxxxxxx> wrote in message
news:dr7f6j$931$1$8300dec7@xxxxxxxxxxxxxxxxxxx
> Does the refresh frequency make any difference to LCDs if they are running
> from analogue signal?

Refresh on an LCD panel is a different animal... You have the backlight,
which is a 60Hz fluorescent lamp and that is a constant that doesn't change.
The panel itself will also have one or two refresh rates and the typical are
60Hz (all LCDs operate at 60Hz, or at least all I know about) and
occasionally 48Hz. Some LCD displays have the ability to accept signals at
higher scan rates, for compatibility reasons, but they still refresh the
displayed image at 60Hz. A few of the very new HDTV LCOS displays (like the
new 65" model from Brillian and the >$20K pro models from JVC and Sony) now
have 120Hz refresh rates. But don't plan to see that on large panel desktop
monitors anytime soon. These are 1/2 to 2/3 inch LCOS chips. 120Hz for LCD
and other non scan-line generating displays is the ultimate target. 120Hz
will provide smooth video playback for 120, 60, 48, 30 and 24 frames per
second. Current 60Hz displays have playback "judder" on 24 and 48 frame/sec
media. Makes it hard to edit 24fps HD and film sources without having a CRT
display or one of those super-expensive LCOS displays. Some studio-grade
LCD desktop monitors also support 24Hz and 48Hz refresh to facilitate this
sort of editing...

LCDs don't need the high refresh rates in order to deliver a smooth image in
normal circumstances because there is no horizontal or vertical scanning,
the entire display simply refreshes at once, all pixels simultaneously. The
response time you see (6, 8, 11, 12, 16 milliseconds as industry norms) is
measured differently from one manufacturer to the next, but it is usually
the time it takes for the display pixels to go from 0 black to 100% white
and back down to 0. Obviously, the faster the better as it eliminates
motion blur. Anything faster than 16ms is ideal for video and gaming and
the eye can still detect differences down to about 8ms. Faster than that is
somewhat of a waste. On a CRT this same effect is called phosphor
persistence. Trinitron style displays have phosphor rise/fall times
approaching in the 3 to 5 ms range. Shadow mask displays are usually in the
6 to 9 ms range. But just as with LCDs there's exceptions to these... I've
seen junk LCD monitors that have 22ms respnses and they're blurry as all
*%&#$ when playing Quake.

> I must admit, I assumed that it didn't because of the refresh rates of the
> screen - 12ms and so on. I am running my secondary monitor off a DVI port
> with an adapter so that I can fit the second monitors VGA cable into it
> and so it is not digital. Will increasing the frequency (when I install
> the right driver!) make a difference?

No difference for the on-screen refresh. However, it may make a difference
as to how the monitor processes the incoming video signal and how that
translates to what transitions to the screen.

You also have to figure that on digital connections (DVI/HDMI), there are
limitations to refresh rates within the standard. Partially due to
conformance, but also bandwidth limitations. The current top resolution for
DVI/HDMI is 1920x1200 @ 60Hz. A dual-link connection supports up to double
that and for 16:10 aspect, a 2560x1600 @ 60Hz is about the best you can get.
Looks damn nice too on the Dell and Apple 30" displays.


.

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