[opendtv] Re: California Prepares to Limit TV Energy Use
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 19 Oct 2009 08:29:34 -0400
Stessen, Jeroen wrote:
> 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.
>>
Actually Bert wrote that. Though I don't disagree.
> 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.
>
>
I was not aware LCD's were that horribly inefficient. I guess that
means if the the back lights were always on (not blinking) then over 95%
of the energy would end up as heat. And, like data centers, in a warm
climate you also end up having to remove that heat with air
conditioning, doubling the expense. Yuck!
> 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.
>
I thought OLED's were better. I still have high hopes for efficient
emissive displays like OLED or lasers that can generate only the light
you need, in the colors you need. But like all LED technologies I
keep hoping, but still waiting. It has been maybe 20 years now I've
been waiting for houses where the rooms are lit by wall size efficient
flat panels that also happen to be video displays. I think even Bill
Gates started to build one once. They will probably arrive along with
our promised flying cars. Still waiting.
- Tom
> 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
>
>
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