LCD Contrast

Archived from groups: rec.photo.digital (More info?)

"Don Stauffer" <stauffer@usfamily.net> wrote in message
news:f3mMe.5$Xh6.580@news.uswest.net...
> 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...

Archived from groups: rec.photo.digital (More info?)

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

Archived from groups: rec.photo.digital (More info?)

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