Re: Contrast ratio
- From: Kotya <kotya.karapetyan@xxxxxxxxx>
- Date: Tue, 14 Apr 2009 01:07:44 -0700 (PDT)
I am not quite sure about the initial question (what the "forward
current of LED-backlight" is) but having worked for some time with one
of the biggest LCD players in the market on the problems of LCD
characterization I'd like to comment on the topic.
There are several different contrast measurements, and several
standards. Each company uses the standard it likes, and sometimes
changes it a little bit to suit its needs in a better way. This makes
the results difficult to compare even for professionals. But the main
problem I see as a user is that nobody actually declares what the
contrast ratio given in the specs should be. Inside the company we had
several different contrast measures: contrast between black and white
spots on the screen, contrast between white spot when viewed in the
direction of the normal and the same spot viewed under an angle
(that's how the viewing angle is defined, but again different vendors
use different acceptable minimum contrast ratio), contrast between the
black and white frames...
The instrument we used was http://www.konicaminolta.com/instruments/products/display/spectroradiometer/cs2000
and the measurements were done in complete darkness (below measurable
with http://www.konicaminolta.com/instruments/products/light/incident-color-meter/cl200
).
A few years ago a concept called dynamic backlight was introduced.
This is also not clearly defined, but the general idea is that the
backlight may be reduced for dark spots or scenes and increased for
light ones. Measured in a dark room, the black-screen-to-white-screen
contrast will then easily reach infinity, since no light is produced
by the black screen and no light is reflected. Some LED backlights can
also significantly improve the contrast between different parts of the
same frame.
As a result, one can get NEC AccuSync 19WV with the specified contrast
of 1000:1 for 95€ and EIZO CG19-K with 450:1 for 1250€.
.
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