[opendtv] Re: California Prepares to Limit TV Energy Use
- From: "Stessen, Jeroen" <jeroen.stessen@xxxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 19 Oct 2009 08:57:50 +0200
Hello,
Did someone call my name ?
Tom Barry wrote:
> Also, the back lights of LCD TVs, when they aren't LED, are fluorescent.
> So my impression is that blinking it off, e.g. to improve black levels,
> might save more energy than going to LEDs? I'm not sure. Jeroen probably
> has the numbers.
I wrote about this for the SID 2006, paper 26.4: "Algorithm for
Contrast Reserve, Backlight Dimming, and Backlight Boosting on LCD".
At that time we were working on a scanning backlight with HCFL tubes
(i.e. your typical TL5 office lighting tubes), that could provide
300% to 400% of the nominal backlight power. So we would typically
run them at 25%-33% duty cycle, and scanning from top to bottom in
sync with the display refresh at 100 or 120 Hz. We could dim them
down to 8% duty cycle or so, and we could boost them for a short time
to 100%. The average power consumption was guarded by a control loop,
and we could select any figure for the average power that we liked.
Thus, we could save significant power from dynamic backlight dimming.
In the mean time, the thick HCFL tubes have been abandoned for LCD
backlighting. Thin CCFL tubes are still the norm, very quickly to be
overtaken by edge-lit and direct-lit LED backlights. Typically these
do not have the power reserve for boosting, but they can be dimmed.
If the duty cycle becomes < 50% or so, then it makes sense to scan
them from top to bottom. This then turns a "100 Hz" TV into a "200
Hz" TV, because the on-time becomes 5 ms or less. It is the on-time
(not the response time !) that determines the motion smear on the
retina, and thus the sharpness of moving objects.
A dimmable backlight, especially if it is addressable (2D dimmable
direct-lit LED backlight), has many advantages:
- improved black level on dark scenes,
- improved viewing angle and color saturation on dark scenes (for
IPS panels anyway),
- improved motion portrayal (when scanning) on dark scenes,
- reduced average power consumption,
- reduced temperature,
- increased life time.
It is no secret (it is demonstrated at every exhibition) that
backlight dimming is the most important tool for reducing the power
consumption, followed by brightness enhancement foils from 3M
Vikuiti and minor improvements to the LCD itself. Given that an
LCD transmits approx. 5% of the light in the on-state, and < 0.01%
in the off-state, there is always a lot of room for improvement.
One person who is fully committed to do something about this, she
designed the very-low-power display for the One Laptop Per Child,
is Mary Lou Jepsen of Pixel-Qi, with offices in California and
Taiwan. See:
http://www.engadget.com/2009/10/17/pixel-qi-e-ink-lcd-hybrid-display-to-debut-on-tablet-next-mont/
Her displays are transflective and they turn to black-and-white in
daylight with the backlight off, with a very good contrast.
It's people like her who set new standards, and I think that it is
wise of the California government to make sure that the competition
stays alert. Without regulation, not enough is going to happen.
Strangely, OLED which is an emissive display that lights up only
when needed, does not yet promise to be much more efficient.
Groeten,
-- Jeroen
Jeroen H. Stessen
Specialist Picture Quality
Philips Consumer Lifestyle
Advanced Technology (Eindhoven)
High Tech Campus 37 - room 8.042
5656 AE Eindhoven - Nederland
The information contained in this message may be confidential and legally
protected under applicable law. The message is intended solely for the
addressee(s). If you are not the intended recipient, you are hereby notified
that any use, forwarding, dissemination, or reproduction of this message is
strictly prohibited and may be unlawful. If you are not the intended recipient,
please contact the sender by return e-mail and destroy all copies of the
original message.
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
Other related posts:
