From: schuster@panix.com (Michael Schuster)
Subject: Re: Black on white w/LCD screen bad?
Date: Thu, 27 Aug 1992 01:08:19 GMT
Organization: PANIX Public Access Unix & Internet, NYC

In article <1992Aug25.141209.23658@cc.ic.ac.uk> cmaae47@cc.ic.ac.uk writes:
>In article <q3cyPB2w163w@coyote.datalog.com>, ferdie@coyote.datalog.com (fred jarvis) writes:
>...
> -- I'll be grateful if somebody can help me out in reversing the video        
> -- on my Everex Tempo LX.  Its background is currently white and the          
> -- foreground is black.  Someone mentioned that this will burn out the        
> -- screen faster, is it true?  If so is there a way to reverse the video?     
>
>On the current backlit or sidelit LCD screens light is retained by closing
>the LCD shutter to create black, white (or rather blueish-green or greenish-
>blue) goes through. Thus there is an extra strain on the pixel for closing
>the shutter and more to convert the energy of the photons to heat.
>
>Thus more black gives more burn-out, but I don't think it is relevant.
>
>For my Commodore (Sanyo) LCD the manufacturer quotes a 8000 hour MTBF, which
>suggests that after about 5500 operating hours half the screens will have 
>failed. At 4 hours usage per day (fairly high for a notebook) we can therefore
>expect half the users being able to use their machines for 5 years without 
>screen trouble.



I forwarded the above to Scott Bruck at the Matsushita Display Technology
Research Laboratory. (He sometimes has trouble posting). Here is his reply:


========begin quoted message================

Date: Thu, 27 Aug 92 08:20:42 JST
From: cmcl2!em.drl.mei.co.jp!sbruck (BRUCK SCOTT)
Return-Path: <sbruck@em.drl.mei.co.jp>
Message-Id: <9208262320.AA03207@harmony2.em.drl.mei.co.jp>
To: sbruck@em.drl.mei.co.jp, schuster@panix.com
Subject: Re: Black on white w/LCD screen bad?
Status: RO

Mike,

	That quote about the photons is very interesting and in everything
I have ever read or heard, I have never heard it discussed in those terms.
I am currently attempting to write a series of posts that will describe in
detail LCD technology, operation, and tetc.  If it ever gets finished, I will
attempt to post it.      

Answer to the question follows:

In order to obtain the highest possible contrast on LCD dot matrix 
displays, they are usually manufactured in what is called "White
Normal Mode."  This means that when no electric field is applied to
the liquid crystal cell, light will pass through.  As a result, a 
white (actualy clear) background with dark text is the simplest method
of operating an LCD.  The method used to drive LCDs also helps to 
prevent the liquid crystal material from failing; every other odd cycle
is driven with an inverse voltage.  For example, the first cycle will be
a positive bias and the following cycle will be an equal but negative bias.
The end result is no net positive or negative charge on the liquid crystal
cell.

I have also read a post mentioning the MTBF, in some cases this needs
to be taken with a grain of salt.  These tests are actually simulated.
By using a higher temperature and a brutal ambient, engineers can
"estimate" when a display will fail.  In other words, picture an 
innocent display at around 50 - 60 C in a greenhouse !  Liquid Crystal
displays are extremely reliable.  They are sealed in a vacuum and the glass
and epoxy seal provides excellent protection from the environment.

In terms of Photnon or heat problems; I really would not be concerned with
this at all.  The polarizers attached to the back and front absorb
more than 60% of the light (I do not have the actual number in front of me).
If there is any heat generated, I seriously doubt much is generated from
4 mm cool cathode florescent lamps, it will be absorbed by the polarizers.
Scott M. Bruck
Matsushita Electric Industrial Co., Ltd.
Display Technology Research Laboratory
Moriguchi-shi, Osaka Japan
SBRUCK@EM.DRL.MEI.CO.JP


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