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LCD Contrast

 
 
Don Stauffer
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      08-16-2005
The thread on displays raises again a question I've had for several
years, since I saw claims for LCD displays of contrast ratios of several
hundred to one.

First of all it implies a very efficient (very nearly 100 percent)
polarizer(s).

Next, it means that control of the rotation of the polarization vector
in the liquid crystal must be VERY accurate. But what about path length
differences with field angle.

Lets say the center pixels ARE controlled that well, and that CR
measurement is taken on axis, aligned with center pixels.

Now, at normal viewing distances, there will be several degrees
difference in viewing angle when viewing pixels near edge of display.
Even if the LC has a high refractive index, there is still some path
length change for off-axis rays.

Do they take this into effect in the control of pixels? Do they assume
you are viewing exactly on axis, and change rotation of polarization of
peripheral pixels compared to central ones? If not, it seems to me when
it is really black at center, it would NOT be really black at edges.
 
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MarkČ
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      08-16-2005

"Don Stauffer" <(E-Mail Removed)> wrote in message
news:f3mMe.5$(E-Mail Removed)...
> The thread on displays raises again a question I've had for several years,
> since I saw claims for LCD displays of contrast ratios of several hundred
> to one.
>
> First of all it implies a very efficient (very nearly 100 percent)
> polarizer(s).
>
> Next, it means that control of the rotation of the polarization vector in
> the liquid crystal must be VERY accurate. But what about path length
> differences with field angle.
>
> Lets say the center pixels ARE controlled that well, and that CR
> measurement is taken on axis, aligned with center pixels.
>
> Now, at normal viewing distances, there will be several degrees difference
> in viewing angle when viewing pixels near edge of display. Even if the LC
> has a high refractive index, there is still some path length change for
> off-axis rays.
>
> Do they take this into effect in the control of pixels? Do they assume
> you are viewing exactly on axis, and change rotation of polarization of
> peripheral pixels compared to central ones? If not, it seems to me when
> it is really black at center, it would NOT be really black at edges.


Contrast ratio claims are VERY misleading, since the means of measuring them
are variable and twisted by manufacturers.
Pay little attention to them in marketing notations...


 
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Pete R
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      08-16-2005
"MarkČ" <mjmorgan(lowest even number here)@cox..net> wrote in message news:NMuMe.2782$ct5.1611@fed1read04...

> Contrast ratio claims are VERY misleading, since the means of measuring them
> are variable and twisted by manufacturers.


As are pixel response times, MTBFs for LCD backlights etc.

> Pay little attention to them in marketing notations...


Good advice. The bottom line is, unless you're spending $2K
or more you can expect your monitor to be a proud member
of a landfill within two years, three tops.


 
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Leonard
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      08-17-2005
Pete R wrote:

> Good advice. The bottom line is, unless you're spending $2K
> or more you can expect your monitor to be a proud member
> of a landfill within two years, three tops.


Really? I've got a bunch of four-to-five year old laptops and
the only screen failures I've seen are due to ribbon cable breakage
in the hinge. I would assume that a screen that spends it's life
perched on a desk rather than being kicked around in a laptop bag
would be more reliable.

I'm with you on contrast ratio/pixel response time claims though.
They would appear to fall in the PMPO category of made-up specs.

- Len
 
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Pete R
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      08-17-2005
"Leonard" <(E-Mail Removed)> wrote in message news:O9MMe.1034$(E-Mail Removed)...
> Pete R wrote:
>
> > Good advice. The bottom line is, unless you're spending $2K
> > or more you can expect your monitor to be a proud member
> > of a landfill within two years, three tops.

>
> Really? I've got a bunch of four-to-five year old laptops and
> the only screen failures I've seen are due to ribbon cable breakage
> in the hinge. I would assume that a screen that spends it's life
> perched on a desk rather than being kicked around in a laptop bag
> would be more reliable.


I'm not referring to screen failures. I'm talking about their
usefulness for color correction and other graphic editing
tasks. LCD backlights lose 50% of their brightness within
three years.


 
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Leonard
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      08-18-2005
Pete R wrote:

> I'm not referring to screen failures. I'm talking about their
> usefulness for color correction and other graphic editing
> tasks. LCD backlights lose 50% of their brightness within
> three years.


I've seen figures quoted between 20,000 and 60,000 hours continuous
use. The oldest desktop LCD I have is three and a half years old and
has probably been switched on for 10,000 hours max so I can't comment
from experience.

- Len
 
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Father Kodak
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      11-18-2005
On Wed, 17 Aug 2005 19:24:30 GMT, Leonard <(E-Mail Removed)> wrote:


>
>I'm with you on contrast ratio/pixel response time claims though.
>They would appear to fall in the PMPO category of made-up specs.
>
>- Len


PMPO = ???

Kodak
 
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Iraxl Enb
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      11-18-2005
>>I'm with you on contrast ratio/pixel response time claims though.
>>They would appear to fall in the PMPO category of made-up specs.
>>
>>- Len

>
>
> PMPO = ???



peak music power output. a totally bogus rating on how
loud a music system can get...

irax.
 
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