LED Apparent Brightness

[Ban]

RST Engineering (jw) wrote:

"Most such white LEDs will be slightly more efficient when moderately
underpowered and will be less efficient when overpowered."

Which speaks directly to white LEDs, but not to LEDs in general. And
what is "slightly" more efficient? If I can put in an average 25%
more power by pulsing and the LED goes 1% less efficient, I've
achieved a 24% gain with no more battery power consumed.

Huh?

These two sentences say the highest efficiency is measured with a
little less than the nominal current, so when you try to increase
the current the efficiency goes down. Maybe you didn't understand it
this way? There is a lot of useful information on these pages, but
not written in spectacular but rather technical manner.

"efficiency" can be measured in a whole bunch of ways. If lamp
output goes down a couple of percent in efficiency with more current,
but the current can be delivered more efficiently, then total
efficiency can be discussed as lamp output as a function of total
power taken from the driving source. That was my original question,
but Klipstein elaborated to the point that I think I understand that
lamp efficiency falls faster than source efficiency when you climb
above nominal current. At least that's what I THINK he said.

Sorry, your logic sucks. Electrical Power is current multiplied by voltage.

Then we get into the question of what "nominal" current means and how
it is specified. I don't think I've seen that number on any of the
data sheets I've perused, be it HP, Kingbright, Toshiba ... or
Mouser. THere are a lot of "recommended" currents, but what is the
basis for recommendation?

Have you really looked at a data sheet? Maybe you should read again Dons
pages how efficiency is defined.

Too many questions, not enough answers.

All answers are there if you would have understood the basic principle of

efficiency.

--
ciao Ban
Bordighera, Italy

 

[Rob Gaddi]

Don Klipstein wrote:

Or find out what green units are used in Upper Darby, PA. They have
gone a few years already quite well. I have not noticed any failures.

I have seen a few reds in Philadelphia with partial failures, but they
could be less-good models (Philadelphia tried several different models, at
least in pilot programs on a few streets) and also most of these could be
about 10 years old already.

A modern red or green LED traffic signal consumes typically about 12
watts maybe a bit less nowadays, and the incandescent it replaces is
probably a 92 watt or 116 watt one.

- Don Klipstein (don@misty.com)

The LED lamps here in Houston seem to all run just fine. Granted every
time we have an electrical storm the entire signal goes out, and we have
an electrical storm about every other week, but that's pretty uniform
across all of the signals, silicon or filament.

 

[John Larkin]

On Mon, 09 May 2005 11:19:27 -0500, Rob Gaddi
<rgaddi@bcm.YUMMYSPAMtmc.edu> wrote:

Don Klipstein wrote:

Or find out what green units are used in Upper Darby, PA. They have
gone a few years already quite well. I have not noticed any failures.

I have seen a few reds in Philadelphia with partial failures, but they
could be less-good models (Philadelphia tried several different models, at
least in pilot programs on a few streets) and also most of these could be
about 10 years old already.

A modern red or green LED traffic signal consumes typically about 12
watts maybe a bit less nowadays, and the incandescent it replaces is
probably a 92 watt or 116 watt one.

- Don Klipstein (don@misty.com)

The LED lamps here in Houston seem to all run just fine. Granted every
time we have an electrical storm the entire signal goes out, and we have
an electrical storm about every other week, but that's pretty uniform
across all of the signals, silicon or filament.

We rarely have lightning here; it's quite a novelty. So something else
is killing the signal lights. I think they have to run the greens at
high current to get the necessary brightness, so they're failing
first.

LEDs run at close to their maximum rated current aren't all that
reliable. Anything that generates light seems to kill itself.

John

 

[Charlie Edmondson]

RST Engineering (jw) wrote:

I started a thread similar to this one over in SEC and didn't really get
anywhere. Let's try it here and see how it goes.


We have a 5 volt source from which we want to drive an LED. For the sake of
discussion, let's presume that with 20 mA into the LED that it drops 2.0
volts. Calculating the resistor isn't difficult -- 150 ohms ought to work.
Calculating the power consumed by the diode isn't any more difficult -- 40
mW.

Now let's put a one-shot in between the source and the LED so that the duty
cycle is 25% at some reasonable frequency above the eye's flicker rate.
Again for discussion, we'll presume 100 Hz.. Assuming that the LED can take
the current, we can pump 80 mA into the LED with this duty cycle, at which
point the LED's voltage rises to 2.5 volts (actual data from the HP data
book). Resistor? 33 ohms ought to work. Power? 200 mW peak, 50 mW
average.

With my limited biotechnical knowledge of the human eye, it would seem as
though the second LED should be brighter. Yet in (admittedly few) bench
observations the second LED was a bit dimmer, if anything. The LED wasn't
getting overly warm, nor did the voltage and current change as time went on,
indicating some moderate thermal stability.

The HP apps note on the subject (AN-1005) goes into a long song and dance as
to HOW to achieve pulse driving an LED, but doesn't come right out and say
that it will be brighter if you do this. But why would they take the time
to show how to do it if it didn't give any benefit?

I'm not understanding something.

Jim


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.

Charlie

 

[John Larkin]

On Mon, 09 May 2005 14:13:16 -0700, Charlie Edmondson
<edmondson@ieee.org> wrote:

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.

Charlie

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


John

 

[R.Lewis]

"RST Engineering (jw)" <jim@rstengineering.com> wrote in message
news:117smgb9f8o0k53@corp.supernews.com...

"Most such white LEDs will be slightly more efficient when moderately
underpowered and will be less efficient when overpowered."

Which speaks directly to white LEDs, but not to LEDs in general. And what
is "slightly" more efficient? If I can put in an average 25% more power
by
pulsing and the LED goes 1% less efficient, I've achieved a 24% gain with
no
more battery power consumed.

25% more power in, 1% less efficient, 24% gain, no more battery power
consumed ?
Magic batteries, magic leds?
I suspect magic mushrooms.

 

[Joop]

Charlie Edmondson <edmondson@ieee.org> wrote:

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.
snip
Charlie

Another only good reason might be if the material has a threshold
below it does not light up, but at the same time the above threshold
current is too much to be applied all the time.
This is the case for some types of GaAs Laser diodes. Details:
http://repairfaq.ece.drexel.edu/sam/CORD/leot/course03_mod11/mod03-11.html
See figure 7 to get the idea.

Joop

 

[Charlie Edmondson]

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

Hi Rich,

Actually, I think heat and power are the main reason. If you have a
very bright LED, they tend to generate enough heat to need a little bit
of heat sinking. As you try to get that many of them together, you
don't have much room for the heat sink. At least the jumbotrons have
room at the back for some fins, or even a little plumbing...

Also, adding up all those 20mA LEDs, that's a considerable amount of power!

Charlie

 

[Jonathan Kirwan]

On Tue, 10 May 2005 14:03:02 -0700, Charlie Edmondson
<edmondson@ieee.org> wrote:

Actually, I think heat and power are the main reason. If you have a
very bright LED, they tend to generate enough heat to need a little bit
of heat sinking. As you try to get that many of them together, you
don't have much room for the heat sink. At least the jumbotrons have
room at the back for some fins, or even a little plumbing...

Also, adding up all those 20mA LEDs, that's a considerable amount of power!

I think that's right. I've got some 16x16 LED panels used in making
large TV-like displays, with each of the LED elements having three LED
dies inside (RGB, tri-color.) So the panel is really 3x16x16 in terms
of numbers of LEDs.

I've got some separated by 5mm, some by 4mm. Can't recall any
separated by 3mm, yet. But all are backed by a large, thick, metal
panel for heat removal. And these units accept three separate
supplies, one for each color, in order to help minimize wasted heat.

It's a lot of power. Perhaps as much as some 80 watts per 16x16
panel, if memory serves. And that's just 256 color pixels. 640x480
is more than a 1000 times as much. 80-100kW would be a LOT OF POWER
to dissipate in a small display. You need lots of AREA to get rid of
that much heat.

Jon

 

[Joop]

Jonathan Kirwan <jkirwan@easystreet.com> wrote:

It's a lot of power. Perhaps as much as some 80 watts per 16x16
panel, if memory serves. And that's just 256 color pixels. 640x480
is more than a 1000 times as much. 80-100kW would be a LOT OF POWER
to dissipate in a small display. You need lots of AREA to get rid of
that much heat.

Jon

Also it would be one huge piece of silicon (crystalline?) Or an
enormouse amount of interconnected small pieces of silicon.

 

[Joop]

Just though of another purpose: the IR remote control.
Here pulses (about 38KHz) are used by the receiver to distinguish the
signal from the ambient light. Shorter bright pulses might even help
in this respect to get further above the noise floor (if this is of
any influence)

 

[John Larkin]

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

 

[John Larkin]

On Tue, 10 May 2005 14:03:02 -0700, Charlie Edmondson
<edmondson@ieee.org> 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

Hi Rich,
Actually, I think heat and power are the main reason. If you have a
very bright LED, they tend to generate enough heat to need a little bit
of heat sinking. As you try to get that many of them together, you
don't have much room for the heat sink. At least the jumbotrons have
room at the back for some fins, or even a little plumbing...

Also, adding up all those 20mA LEDs, that's a considerable amount of power!

LEDs are at least as efficient as CRTs and more efficient than a ccfl
backlight being pushed through lcd pixel polarizers and color filters.
So for a given brightness, an led panel should run cooler than a crt
or a color lcd of equal display area.

640x480x3 = 921,600 led's. If you ran all of them at 20 mA
simultaneously, that would be about 36 kilowatts, making enough light
to blind everybody in the room and toast the guy in the chair.

The reason nobody makes small vga-level displays from led's is cost.

John

 

[John Fields]

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?

---
With a white backlight running CW and three planes of filters in front
of it, all you have to do is attenuate what you don't want to come
through. The other way, with three LEDs per pixel, you've got to send
enough current into each of the LEDs comprising the triad to get it to
radiate just exactly the right hue at just exactly the right time.

That means that, in order to push current through each LED in the
triad in order to get the pixel to radiate the proper color, turning
the LEDs in that triad on for short periods of time would be
necessary. Because of that, the array would radiate. That's not a
good thing, and using nano (or pico) amps to do do the color selecton
through attenution seems to make a lot more sense.

--
John Fields
Professional Circuit Designer

 

[John Fields]

On Tue, 10 May 2005 16:13:15 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 10 May 2005 14:03:02 -0700, Charlie Edmondson
edmondson@ieee.org> 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

Hi Rich,
Actually, I think heat and power are the main reason. If you have a
very bright LED, they tend to generate enough heat to need a little bit
of heat sinking. As you try to get that many of them together, you
don't have much room for the heat sink. At least the jumbotrons have
room at the back for some fins, or even a little plumbing...

Also, adding up all those 20mA LEDs, that's a considerable amount of power!


LEDs are at least as efficient as CRTs and more efficient than a ccfl
backlight being pushed through lcd pixel polarizers and color filters.

---
Really?

How about some numbers?
---

So for a given brightness, an led panel should run cooler than a crt
or a color lcd of equal display area.

---
Really?

How about some numbers?
---

640x480x3 = 921,600 led's. If you ran all of them at 20 mA
simultaneously, that would be about 36 kilowatts, making enough light
to blind everybody in the room and toast the guy in the chair.

---
OK, but since they wouldn't all be running simultaneously, what do
you think the average dissipation per pixel would be? And the average
dissipation for the array?

That is, LEDs VS whatever it is they call those light switches...
---

The reason nobody makes small vga-level displays from led's is cost.

---
Duh...

--
John Fields
Professional Circuit Designer

 

[John Larkin]

On Tue, 10 May 2005 19:08:27 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 10 May 2005 16:13:15 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 10 May 2005 14:03:02 -0700, Charlie Edmondson
edmondson@ieee.org> 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

Hi Rich,
Actually, I think heat and power are the main reason. If you have a
very bright LED, they tend to generate enough heat to need a little bit
of heat sinking. As you try to get that many of them together, you
don't have much room for the heat sink. At least the jumbotrons have
room at the back for some fins, or even a little plumbing...

Also, adding up all those 20mA LEDs, that's a considerable amount of power!


LEDs are at least as efficient as CRTs and more efficient than a ccfl
backlight being pushed through lcd pixel polarizers and color filters.

---
Really?

How about some numbers?

A ccfl is maybe 30% efficient, DC-to-light. An lcd pixel with color
filter can't theoretically be better than 16% (33% for the color
filter, 50% for the polarizer) and in real life is maybe half that at
best. So my Dell lcd screen is at best 5% efficient, not counting the
electronics. Probably less. And the 5% is when all pixels are full-on,
screen white, which few actually are; its dissipation does *not* go
down even when pixels are black... the light is just wasted.

I've seen the assumption of 5% panel transmission used for lcd's.
Multiply that by 30% for the ccfl, you get 1.5% overall.

Good LEDs are, what, 20% efficient? And when you dim an led pixel, it
uses proportionally less power, unlike the lcd. Zero when black.

I don't have numbers on CRTs, except to note that at equal brightness
they dissipate a *lot* more heat than an lcd screen.

So for a given brightness, an led panel should run cooler than a crt
or a color lcd of equal display area.

---
Really?

Really.

How about some numbers?

See above.

John

 

[Jonathan Kirwan]

On Tue, 10 May 2005 16:13:15 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

LEDs are at least as efficient as CRTs and more efficient than a ccfl
backlight being pushed through lcd pixel polarizers and color filters.
So for a given brightness, an led panel should run cooler than a crt
or a color lcd of equal display area.

The "pixels" in the LED display *are* fairly bright and you are right
that not nearly as much power would be required for a readable display
as is used in these "outdoor" display systems.

I'd be interested to see a real examination of efficiency comparisons,
though.

640x480x3 = 921,600 led's. If you ran all of them at 20 mA
simultaneously, that would be about 36 kilowatts, making enough light
to blind everybody in the room and toast the guy in the chair.

I've stood in front of these wall-sized displays as they placed NTSC
pictures on them and they don't toast you. They *are* bright! But it
appears to me that far and away most of the energy is wasted as heat,
not emitted as visible light.

The reason nobody makes small vga-level displays from led's is cost.

Well, it would be expensive. These units I have were, in largish
quantities, some $70-90 each. I don't know how much of that was
bonding and how much was heat-sinking, so if the light levels were
reduced perhaps a fair percent of the cost could be stripped out, but
it still would be pricey. They used 6 DACs in each panel, PWM within
that for % brightness control, and each little die was carefully
placed and bonded behind an individual plastic lens.

I have to believe the expense would remain fairly high for bonding a
million dies into anything, regardless of the power issues. Not to
mention trying to support controlling apparent color of each pixel at
fairly high frame rates.

Jon

 

[Don Klipstein]

In article <42812186$1@news.cadence.com>, Charlie Edmondson 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

Hi Rich,
Actually, I think heat and power are the main reason. If you have a
very bright LED, they tend to generate enough heat to need a little bit
of heat sinking. As you try to get that many of them together, you
don't have much room for the heat sink. At least the jumbotrons have
room at the back for some fins, or even a little plumbing...

Also, adding up all those 20mA LEDs, that's a considerable amount of power!

I think that with 307,200 of each color, you will get enough light with
a fraction of a milliamp apiece, less than 1/10 of a milliamp for InGaN
green and blue pixels.

- Don Klipstein (don@misty.com)

 

[Jonathan Kirwan]

On Wed, 11 May 2005 01:03:41 +0000 (UTC), don@manx.misty.com (Don
Klipstein) wrote:

I think that with 307,200 of each color, you will get enough light with
a fraction of a milliamp apiece, less than 1/10 of a milliamp for InGaN
green and blue pixels.

Call it 2mW per pixel, roughly. 307k of them would be about 615
watts, with all of them lit. Probably have to add a meaningful
percentage for driver overheads, though.

Anyone got a wire-bonder, a fair length of gold wire, and some spare
time?

Jon

 

[John Larkin]

On Wed, 11 May 2005 01:17:18 GMT, Jonathan Kirwan
<jkirwan@easystreet.com> wrote:

On Wed, 11 May 2005 01:03:41 +0000 (UTC), don@manx.misty.com (Don
Klipstein) wrote:

I think that with 307,200 of each color, you will get enough light with
a fraction of a milliamp apiece, less than 1/10 of a milliamp for InGaN
green and blue pixels.

Call it 2mW per pixel, roughly. 307k of them would be about 615
watts, with all of them lit. Probably have to add a meaningful
percentage for driver overheads, though.

That's doing the math backwards. Assume 3 watts of actual light
(that's probably generous) and 10% led efficiency (which is
pessimistic) you get 30 watts total input power.

John