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leon
Guest
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 Posted:
Wed Feb 23, 2005 2:52 pm Post subject:
LCD display modes in modern laptops?! |
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Hi all, firstly am not sure if this is the right newsgroup, if not -
please point to the one that is...
I would like to establish the exact way most laptop LCD displays work in
(if any specific info re. iBook is present - it will be most welcome).
I am aware of the general theory of LCD functionality (e.g. use of
polarised filters and applying voltage to crystal molecules to untwist
them)... but... there are essentially two mode for LCD displays to work
in (http://www.altadox.com/lcd/knowledge/lcd_display_modes.htm):
positive mode - this is where BLACK is achieved by fully turning the
pixels ON (i.e. applying the voltage to them) which is kind of opposite
to the way CRT monitors work
negative mode - the opposite of positive (i.e. WHITE is the result of
fully tuning the pixel ON in terms of applying a voltage to it)...
i would like to know which mode is used by most laptops (esp macs).
This is important for a number of reasons, one of which is the default
"blackness" in some of the screensavers and autopower display managers.
Whilst displaying full black on CRT monitors actually provides power
saving and "time off" for relevant pixels, in some LCD displays this may
be actually driving corresponding pixels (i.e. the ones that display
black) fully.
Kind regards,
Leon.
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CWatters
Guest
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| Posted:
Wed Feb 23, 2005 2:55 pm Post subject:
Re: LCD display modes in modern laptops?! |
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"leon" <svz@iprimus.com.au> wrote in message
news:421c43b4$1@duster.adelaide.on.net...
| Quote: | Whilst displaying full black on CRT monitors actually provides power
saving and "time off" for relevant pixels, in some LCD displays this may
be actually driving corresponding pixels (i.e. the ones that display
black) fully.
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That doesn't matter because the LCD backlight is what burns most of the
power. True power saving modes turn off the backlight.
If the backlight is on it doesn't matter much if the display is all black or
all white - except that the panel may get warmer when displaying an all
black image. |
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leon
Guest
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| Posted:
Wed Feb 23, 2005 6:24 pm Post subject:
Re: LCD display modes in modern laptops?! |
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ok, i got the point, thanks...
but i still would like to know the display mode (ie positive or
negative) used by LCD laptops - even if only for the purposes of not
"wearing out" pixels (ie not applying voltage on them) in the
"background" areas of display (e.g. terminal window). I also understand
that prolonged display of static images (e.g. task bar in window$ os)
has a non-permanent "burn in" on LCD displays and this is a result of
pixels being in "on" state for continuous amount of time. I realise that
the net effect of either display mode on lifetime of a pixel is rather
minimal, but still, would be nice to know...
CWatters wrote:
| Quote: | "leon" <svz@iprimus.com.au> wrote in message
news:421c43b4$1@duster.adelaide.on.net...
Whilst displaying full black on CRT monitors actually provides power
saving and "time off" for relevant pixels, in some LCD displays this may
be actually driving corresponding pixels (i.e. the ones that display
black) fully.
That doesn't matter because the LCD backlight is what burns most of the
power. True power saving modes turn off the backlight.
If the backlight is on it doesn't matter much if the display is all black or
all white - except that the panel may get warmer when displaying an all
black image.
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CWatters
Guest
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| Posted:
Wed Feb 23, 2005 10:58 pm Post subject:
Re: LCD display modes in modern laptops?! |
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"leon" <svz@iprimus.com.au> wrote in message
news:421c758f@duster.adelaide.on.net...
| Quote: | ok, i got the point, thanks...
but i still would like to know the display mode (ie positive or
negative) used by LCD laptops -
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Sorry I'm only familure with 7 segment types. On those with no voltage
applied the crystals are twisted and the display is transparant/white. |
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Bob Myers
Guest
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| Posted:
Thu Feb 24, 2005 2:34 am Post subject:
Re: LCD display modes in modern laptops?! |
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"leon" <svz@iprimus.com.au> wrote in message
news:421c758f@duster.adelaide.on.net...
| Quote: | ok, i got the point, thanks...
but i still would like to know the display mode (ie positive or
negative) used by LCD laptops - even if only for the purposes of not
"wearing out" pixels (ie not applying voltage on them) in the
"background" areas of display (e.g. terminal window).
|
It doesn't matter, because this is NOT a "wear-out" factor for
LC displays. In terms of possible damage to the LC material
itself, the main concern (assuming that the unit isn't subjected to
temperature extremes) is the application of a long-term net
DC voltage across the LC cell. This does not occur even when
the pixels are "on" (whether "on" is a "black" state or a "white"
one), as the polarity of the drive is reversed, typically from frame
to frame.
Having said that, there are actually a number of different LC
modes in use in laptops, some "positive" and some "negative." I
believe the most common would still be a standard twisted-nematic
cell with crossed polarizers, which is normally transmissive when off
(which I think you're calling "negative," but please see below),
but that's by no means the only type. (This results mostly from
manufacturing convenience - building the display with the
polarizers crossed means that for both the top and bottom glass,
the polarizer is aligned with the "rubbing" layer.)
Actually, I need to now insert a minor correction re terminology
- "positive mode" and "negative mode," when used with LCDs,
often does not refer to whether the pixel is "white" when driven,
but rather to the overall appearance of the display - i.e., does it
give a "black text on white" appearance or "white text on black"?
Here, though, "positive" is used as it would be with respect to
typical text displays - it refers to black text on a white background.
Which often means that the LC itself is actually operating in the
what you might call a "negative" mode - the segments that make up
the characters are black when driven! So you need to be very
careful to understand the context in which these terms are being
used.
| Quote: | I also understand
that prolonged display of static images (e.g. task bar in window$ os)
has a non-permanent "burn in" on LCD displays and this is a result of
pixels being in "on" state for continuous amount of time. I realise that
the net effect of either display mode on lifetime of a pixel is rather
minimal, but still, would be nice to know...
|
Not really; there was a problem with this in the early days of
LCDs (the problem is generally referred to as "image sticking,"
and if the drive were held in one state long enough, it could in
some cases become permanent), but it's pretty much a non-issue
with most modern displays. (Note that this statement may not
apply to the really cheap monochrome, passive-drive types
used in some applications - I'm referring only to modern
active-matrix panels as used for notebooks, monitors, etc..)
Bob M. |
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