[ltp] 770X TFT

[Mick McQuaid]

... regarding a message from Christopher Gavin on Jul 25:
> I have a 770X and I'm not sure if the panel is 'dogey' or not. 
> 
> The colours all appear to be fine, but white appears as a slightly yellow/off white.
> 
> Is this just a feature of these older technology panels?

Yeah, they had not perfected white back in 1998.
The newer panels have white, and some even "whiter
than white."

> 
> Its 1280x1024 in 16 bit and the whites look white at an extreme viewing angle (ie the thing is folded right out and I look down on it) but upright from desk height it all looks to be tinted yellow. 
> 

Maybe you should only look at it from an extreme
angle?

> Its not a string tint, the brightness is still fine, and there's no flicker. 
> 
> Could it just be an 'aged' panel? Perhaps owned by a smoker or someone who cleaned it with furniture polish?

There could be a lit cigarette inside, producing a
small amount of yellowish smoke.  There probably
isn't much air inside.  It should go out eventually.

> 
> Or am is it a tell tale sign of something more progressively fatal?

Seriouslie, mine is still perfect if
dimmer than when new in October 1998.

I did check and found an LCD mfr website that
mentions the following in a tech report---the good
news is that it suggests replacing the fluorescent
lamp rather than the panel.  (I hope that's good
news!)

Anecdotally, I have heard the backlight aging is
sped up by operating at consistently high ambient
temperatures.  Perhaps the prev owner lived in
Death Valley.

Anyway, here is what Landmark Technology had to
say.  This makes me wonder whether it is cheap /
feasible to replace the backlight.  The real
eye-opener is the 2300 hours figure:

    We noticed that all the backlights under test
    became more yellow in color than the non-operated
    control unit. As a result of this, we started to
    monitor the backlight chromaticities (x, y) on all
    the life tests conducted after summer of 1995.
    The C033 test reveals a noticeable backlight
    chromaticity shift toward yellow at as early as
    2300 hours. This yellow color shift increases as
    time goes by, becoming quite serious at about
    5,000 hours and then the rate of increase slows
    down.  The yellow shift in backlight color may
    cause some concern in LCD applications where the
    color fidelity is important. A major portion of
    the yellow shift is caused by the yellowing (or
    darkening) of the backlight materials. These
    include diffusers, reflectors, adhesives and some
    others.  By analyzing and isolating the bad
    materials, Landmark has reduced this yellow color
    shift problem significantly in the last three
    years.

-- 
Mick McQuaid, mcquaid@u.arizona.edu
              520-621-4074 office / voice mail