LCD Contrast

Discussion in 'Digital Photography' started by Don Stauffer, Aug 16, 2005.

  1. Don Stauffer

    Don Stauffer Guest

    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.
    Don Stauffer, Aug 16, 2005
    #1
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  2. Don Stauffer

    Mark² Guest

    "Don Stauffer" <> wrote in message
    news:f3mMe.5$...
    > 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...
    Mark², Aug 17, 2005
    #2
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  3. Don Stauffer

    Pete R Guest

    "Mark²" <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.
    Pete R, Aug 17, 2005
    #3
  4. Don Stauffer

    Leonard Guest

    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
    Leonard, Aug 17, 2005
    #4
  5. Don Stauffer

    Pete R Guest

    "Leonard" <> wrote in message news:O9MMe.1034$...
    > 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.
    Pete R, Aug 17, 2005
    #5
  6. Don Stauffer

    Leonard Guest

    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
    Leonard, Aug 18, 2005
    #6
  7. Don Stauffer

    Father Kodak Guest

    On Wed, 17 Aug 2005 19:24:30 GMT, Leonard <> 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
    Father Kodak, Nov 18, 2005
    #7
  8. Don Stauffer

    Iraxl Enb Guest

    >>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.
    Iraxl Enb, Nov 18, 2005
    #8
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