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LCD display modes in modern laptops?!

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

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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.

Reply to
leon
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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.

Reply to
CWatters

ok, i got the point, thanks...

but i still would like to know the display mode (ie positive or negative) used by LCD lapt>

Reply to
leon

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.

Reply to
CWatters

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.

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.

Reply to
Bob Myers

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