LED displays: some comments and observations.
LED displays: some comments and observations.
- Subject: LED displays: some comments and observations.
- From: tom lianza <email@hidden>
- Date: Thu, 06 Dec 2007 08:25:51 -0500
Hi to all,
There certainly has been a lot of speculation on this forum about Huey,
i1Displays, filters, fields of view etc. I don't want to talk about
specific combinations of product with a particular customer. Rather
than get into trouble for something I might say that may violate an NDA,
I will simply correct Graeme Gill's comments when I feel he has made a
mistake. So here goes...actually, there really aren't any corrections
at this moment, but I'm keeping an eye on the guy :) I want to
emphasize that to the best of my knowledge, Graeme has no affiliation
with X-rite. He is a very knowledgeable researcher and while I may
occasionally disagree with him, he is normally right on target.
Led backlit displays are a relatively new technology and one should
expect that there will be a long learning curve in this market. The LED
technologies do not optimally align with the filter sets of the LCD
panels in use today. Changing the filtration in a panel is a rather
monumental, high risk, undertaking, so you are going to see this issue
for a relatively long time. The reason the LED panels are hard to get,
is that they hard to build at any price, and it is nearly impossible to
make money at the price they are selling at.
The increase in Gamut achieved by the LED backlight is found mostly in
the green. Rather than narrowing the bandwidth and increasing the
output, physics has demanded that the dominant wavelength of the LED
shift to a lower dominant wavelength than a filtered CCFL lamp.
(Roughly 550nm -> 520-535). This results in an increase of gamut, but
there are some real problems lurking here. The range of dominant
wavelengths for the LED are a strong function of temperature and
chemistry. For any given LED, the center wavelength and optical
bandwidth of the signal changes with temperature. From cold start to
maximum operating temperature, I have measured an xy chromaticity change
on the order of .013 . (Note, that's one zero beyond the decimal point,
not two.) If you look at the spectrum of the various choices of green
leds you will see that their rising edge crosses the rising edge of the
y-bar CMF and falls squarely in the interaction region between the z,x
and y cmf's . What does this mean? It means that it is very difficult
to measure chromaticities accurately with any instrument at any price.
The difference between two very expensive spectral instruments can
easily be .008 when measuring the same source instantaneously. There is
another issue as well. If you believe that the cmf's are based upon
human visual experiments and represent an "average", one should expect a
rather high degree of observer differences when looking at the same
displayed color. In short, you got your gamut, but it's probably not
the same gamut for the guy sitting next to you. If you have an issue
with inter-instrument agreement now, matters will only get worse with
these new technologies.
Now there have been some comments about issues of choice of bundled
product by region. If you have ever done business on a world wide basis,
you understand that your product sells in the context of a local
currency and your profit is reflected in the currency of the nation of
incorporation. The dollar is extremely low. An importer can buy a US
made product very cheaply, and make a handsome profit by selling it in a
region that has a high currency/dollar ratio. The same is not true for
the US. The US market is killing the display industry. Prices for
displays are falling quicker than the dollar. Keep in mind what Graeme
has said about the performance difference between a Huey and and
i1Display. In a bundled situation, on a high end display with custom
software, there is essentially no difference in performance. It is not
the case that the US is any less critical about color, it is simply a
question of a manufacturer staying alive through this very tough time,
by making intelligent technical decisions that respect the financial
realities.
I hope this answers some questions and I suspect that it will generate
more thoughtful comments as well.
Take care,
Tom Lianza
X-rite corporation.
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