LED Apparent Brightness

[Ban]

John Larkin wrote:

Um, I suggested using sequential RGB led's as a *backlight* for an
LCD... didn't I? Not many led's, lots of lcd pixels.

Instead of having a pixel per color, each lcd pixel would handle all
three colors, sequentially, so you get a 3x improvement in pixel
density for free. And there would be no color filters, so light usage
efficiency goes up at least 3:1. The only bug is that most lcd's are
too slow to switch at the required speed, say 150 Hz or so.

There's an article in EDN (?) this month; some projection displays are
indeed using fast lcd's illuminated through spinning color wheels.
Still wastes light.

Just yesterday came this free LED demo board from Philips with tiny 3-colour
SMD-LEDs. Those would really make something neat.
http://www.semiconductors.philips.com/acrobat_download/literature/9397/75013487.pdf

--
ciao Ban
Bordighera, Italy

 

[John Larkin]

On 10 May 2005 20:18:07 -0700, "mike742" <gqrxzy8974@ftml.net> wrote:

Someone built one -- a large one -- the NASDAQ sign in Times Square.

Blue LEDs, digital TV bring daylight-bright signs to masses
http://www.edn.com/article/CA46772.html

Saco Smartvision built the overall sign from 320-mm-sq modular panels,
which each contain an array of 16×16 pixels, totaling 256 pixels. Each
30×30-mm pixel, in turn, comprises eight surface-mounted LEDs: two
blue ones in the middle and two greens and a red on either side (Figure
1). The side-by-side arrangement of 8200 panels yields a
1600-pixel-wide, 2000-pixel-high screen. If you do the math, you'll see
that this arrangement yields nearly 2.1 million pixels and 16.8 million
LEDs. The sign measures 36.6m (120 ft, or eight stories) tall and 27.4m
(90 ft) wide. If you go further with the math, you'll see a discrepancy
between the area of the sign and the stated number of panels the vendor
used to build it. This situation is not a case of playing with the
specifications; it occurs because the sign's surface is not an unbroken
solid but instead has 30 cutouts for the building's windows.
...
Power consumption of the Nasdaq sign is 60W/ft2 (540W/m2).
...

So, what's it cost?

John

 

[Robert Baer]

Rich Grise wrote:

On Mon, 09 May 2005 15:05:21 -0700, John Larkin wrote:

On Mon, 09 May 2005 14:13:16 -0700, Charlie Edmondson

There is only one good reason to pulse a light source to get brighter
illumination when multiplexing is not needed... if you are matching to a
shuttered imager. I had an application that I was developing, in which
we were going to use an IR filter in front of a standard CMOS imager,
adn then use a pulsed IR source with a short pulsewidth matched to an
equally short shutter time on the camera. By sync'ing these together,
the IR illuminator could be the predominate light source, overpowering
even daylight, while still maintaining eye safety.

Too bad LCDs are so slow. The ideal backlight would be sequentially
pulsed R-G-B led's.


But, um, is it seriously unrealistic to contemplate a panel of RGB LEDs,
say, 640 x 480, all by themselves, being pixels? Like a micro-jumbotron?
Frankly, I've been wondering about that ever since I started reading about
the various technologies that have been studied for making flat-screen
displays. Is it just that it would be so prohibitively expensive?

Thanks,
Rich

In downtown Portland OR there is a billboard right by a major road

that is made with an array of R, G, B *bright* LEDs.
It has been in use for over a year (maybe longer) and was replaced
and/or refurbished - it is brighter now than before.
So, "prohibitively" expensive would not seem to be a factor..

 

[Robert Baer]

John Larkin wrote:

On Tue, 10 May 2005 20:37:46 GMT, Rich Grise <richgrise@example.net
wrote:


On Mon, 09 May 2005 15:05:21 -0700, John Larkin wrote:

On Mon, 09 May 2005 14:13:16 -0700, Charlie Edmondson

There is only one good reason to pulse a light source to get brighter
illumination when multiplexing is not needed... if you are matching to a
shuttered imager. I had an application that I was developing, in which
we were going to use an IR filter in front of a standard CMOS imager,
adn then use a pulsed IR source with a short pulsewidth matched to an
equally short shutter time on the camera. By sync'ing these together,
the IR illuminator could be the predominate light source, overpowering
even daylight, while still maintaining eye safety.

Too bad LCDs are so slow. The ideal backlight would be sequentially
pulsed R-G-B led's.

But, um, is it seriously unrealistic to contemplate a panel of RGB LEDs,
say, 640 x 480, all by themselves, being pixels? Like a micro-jumbotron?
Frankly, I've been wondering about that ever since I started reading about
the various technologies that have been studied for making flat-screen
displays. Is it just that it would be so prohibitively expensive?

Thanks,
Rich


Um, I suggested using sequential RGB led's as a *backlight* for an
LCD... didn't I? Not many led's, lots of lcd pixels.

Instead of having a pixel per color, each lcd pixel would handle all
three colors, sequentially, so you get a 3x improvement in pixel
density for free. And there would be no color filters, so light usage
efficiency goes up at least 3:1. The only bug is that most lcd's are
too slow to switch at the required speed, say 150 Hz or so.

There's an article in EDN (?) this month; some projection displays are
indeed using fast lcd's illuminated through spinning color wheels.
Still wastes light.

John


Spinning color wheel? Is that by CBS? Does RCA have something

different? Do i add that to my brand new black and white television for
color?

 

[Jonathan Kirwan]

On Wed, 11 May 2005 06:46:09 GMT, Robert Baer
<robertbaer@earthlink.net> wrote:

Rich Grise wrote:

On Mon, 09 May 2005 15:05:21 -0700, John Larkin wrote:

On Mon, 09 May 2005 14:13:16 -0700, Charlie Edmondson

There is only one good reason to pulse a light source to get brighter
illumination when multiplexing is not needed... if you are matching to a
shuttered imager. I had an application that I was developing, in which
we were going to use an IR filter in front of a standard CMOS imager,
adn then use a pulsed IR source with a short pulsewidth matched to an
equally short shutter time on the camera. By sync'ing these together,
the IR illuminator could be the predominate light source, overpowering
even daylight, while still maintaining eye safety.

Too bad LCDs are so slow. The ideal backlight would be sequentially
pulsed R-G-B led's.


But, um, is it seriously unrealistic to contemplate a panel of RGB LEDs,
say, 640 x 480, all by themselves, being pixels? Like a micro-jumbotron?
Frankly, I've been wondering about that ever since I started reading about
the various technologies that have been studied for making flat-screen
displays. Is it just that it would be so prohibitively expensive?

Thanks,
Rich

In downtown Portland OR there is a billboard right by a major road
that is made with an array of R, G, B *bright* LEDs.
It has been in use for over a year (maybe longer) and was replaced
and/or refurbished - it is brighter now than before.
So, "prohibitively" expensive would not seem to be a factor..

Yes, I believe the one on/near 6th avenue just south of Portland State
University, on the road going between there and Oregon Health Sciences
University.

Jon

 

[Rich Grise]

On Mon, 09 May 2005 15:05:21 -0700, John Larkin wrote:

On Mon, 09 May 2005 14:13:16 -0700, Charlie Edmondson

There is only one good reason to pulse a light source to get brighter
illumination when multiplexing is not needed... if you are matching to a
shuttered imager. I had an application that I was developing, in which
we were going to use an IR filter in front of a standard CMOS imager,
adn then use a pulsed IR source with a short pulsewidth matched to an
equally short shutter time on the camera. By sync'ing these together,
the IR illuminator could be the predominate light source, overpowering
even daylight, while still maintaining eye safety.

Too bad LCDs are so slow. The ideal backlight would be sequentially
pulsed R-G-B led's.

But, um, is it seriously unrealistic to contemplate a panel of RGB LEDs,
say, 640 x 480, all by themselves, being pixels? Like a micro-jumbotron?
Frankly, I've been wondering about that ever since I started reading about
the various technologies that have been studied for making flat-screen
displays. Is it just that it would be so prohibitively expensive?

Thanks,
Rich