CREE RGB white passes CCFL efficiency

Cree's backlighting solution, on show at the Society of Information Displays (SID) meeting in Boston this week, has a power consumption of 40 watts. Cree says that this compares with 100 watts for other LED backlighting solutions and 45 watts for CCFL-based solutions.

“Initially, LED-based backlighting solutions for larger LCD monitors and televisions were applauded for significantly improving color rendering,” says Jerry Simmons, who manages the Solid State Lighting R&D Program at Sandia National Laboratories. “It’s now clear that energy savings can also be significant if the backlighting system is designed for high energy efficiency.”

Cree says that it will make its backlighting solution commercially available for use in LCD computer monitors and televisions by late 2005.

http://ledsmagazine.com/articles/news/2/5/20?alert=1

Guess some of the efficiency gain in this application may be optical gain, with better spreader films or reflectors.

Do wonder if RGB arrays are going to be a better bet for general lighting applications than phosphor based white solutions. Longetivity, as in lower lumen depeciation, looks better, and patent squabbles aside, CT tuning may be handy.

Adam

I personally think RGB arrays with active feedback will be a better bet than phosphor-based LEDs for general lighting. Besides the ability to tune color temperature (which means the lamp sellers can only stock one part in each size instead of the usual 5 or 6), you can even make colored light, and by using more than three wavelengths you can approach a CRI of 100. I think the patent issues may have to do with specific methods of mixing the colors rather than just the concept of using RGB LEDs. After all, colored lights have been mixed ever since the invention of the electric light. I don't see how someone could patent the concept.

Tend to agree for general lighting RGB+ arrays are probably way forward, mebbe Lamina are onto something.

As far as U.S. patents go, you may be suprised or just plain shocked:

http://www.svision.com/ledalliance

Adam

I personally don't think that patent will hold up in the courts. Also, it's only a patent for using PWM to mix colors. You can always just use different DC drive levels for each color to accomplish the same thing. In fact, it's better to do it that way because you take an efficiency hit with PWM as opposed to simply driving at reduced current.

The CREE patent looks a little like the Lumileds backlighting system...unless I've got it wrong and one of them is licensing from th other.....ie put RGB into the LCD backlight instead of white, make sense not to waste unneeded spectrum, as the LCD filters will just block it.....I'm suprised there isn't any issue between these two.

regarding CK and their patents, has anyone heard of them going after the little guys (ie me!) in the RGB world. I'm seeing a bunch of these cheap RGB lights and lamps, using simple transistor PWM sequencers, a bit boring but they're PWMing an LED, no doubt CK will be feeling something soon from these mass produced things affecting their bottom product range.....just how narky are CK going to get trying to get a cut everytime someone switches a LED on and off rapidally? Doesn't make sense....

phil

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rgbphil said:
.....just how narky are CK going to get trying to get a cut everytime someone switches a LED on and off rapidally? Doesn't make sense....


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That's why this "patent" is being so vigorously fought. It's akin to someone patenting fire. PWM has been around for literally decades in one form or another. A great example of it is the common lamp dimmers which use triacs to chop the duty cycle of the AC waveform. Another example is thyristor motor controls on electric trains. The concept of PWM has even been applied to LEDs for well over a decade. So now CK comes along and applies PWM to a few colors at the same time and wants a patent for it? It makes me puke to think the patent office actually fell for that. There was nothing novel or creative about the idea. Maybe if they patented a unique feedback circuit to get consistent color as the LEDs degrade at different rates they would have something worthy of a patent, but not here.

Actually someone has already done the compensation over time thing, jtr1962.

A good search of patents reveals there are a number of different patents covering other areas where folks are mixing RGB, and using sensor feedback. In particular, you will find one that uses three photodiodes with R, G, B filters, and another that utilzes four, the last being "white" or combined brightness.

Some of the patents are found in strange applications, at first thought, such as paint matching, but a tiny bit of thought helps you understand why. Another is in a automotive mirror. Some cover photodiodes, phototransistors, photocells, and various other light measurement devices.

In fact, if you poke around on Agilent's site, you will find a sensor array/microcontroller specifically designed for the color control and compensation (including temperature), they go for about 35.00 ea in volume.

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just how narky are CK going to get trying to get a cut everytime someone switches a LED on and off rapidally? Doesn't make sense....


[/ QUOTE ]

Try marketing it in the U.S. and find out....

It costs CK very little to send a cease and desist letter, it will cost you a lot more to defend your position.

CK have got a lot of outside investment from selling the idea to non technical investors that `their` colour changing LED technology is proprietary and Patent protected and will generate a revenue stream from not just manufacturing but licensing `their` technology to others.

Colour Temperature tuneable is another concept that CK along with Cunningham, inventor of the Source 4 theatre spotlight, are attempting to patent.i.e. using other colours in addition to RGB.

Adam

I wonder if they'd be terrified if I sent them a cease and desist letter! Actually am a bit worried about the demonic pact that John Howard has made wrt to the free trade agreement and these sorts of issues....any info welcome.

Newbie, Silicon Chip magazine June 2005 has an article on a colour sensor from TAOS...looks good, I've ordered one and hopefully will be able to use it to calibrate LED arrays....hopefully, I'm not sure about the impact of having only three sprectrum points to measure from....should be a good toy to play with anyway...the sensor is the TAOS TCS230. Anymore info on those applications you mentioned?

phil

Watch out for the ppm drift per degree C on that part, if you have to operate over temperature ranges.

Also, even holding temperature at 25 degrees C, notice how the frequency on the green photodiode can be from 8 to 19.2 KHz. Thats over a 2 to 1 range... Hopefully the device doesn't drift much with time, so you might be able to calibrate each device to dial out the error.

Watch out for dark current. The no light output vs. temperature. You may see alot of error here.

Depending on what you are doing, a BG-38 or Hoya IR-cut filter may be rather important, since the device has very significant near IR response. Anything around the sun or incandescent lighting may need it. Also consider the influence of any external light sources, as far as your color measurement.

Your eye has three cones which give you a color for light...
Quite a number of low cost colorimeters and color matching equipment utilize a three color sensor based system.

BTW, a number of these devices utilize R,G,B combo photodiodes from Hamamastu. You have several device options here. Here:
http://usa.hamamatsu.com/index.php?id=13198562&language=1&
http://usa.hamamatsu.com/index.php?id=13196718&language=1&
http://usa.hamamatsu.com/index.php?id=13188081&language=1&

Good read to learn basics of photodiodes, which form the heart of many light and color measuring equipment:
http://usa.hamamatsu.com/assets/applications/SSD/photodiode_technical_information.pdf

Agilent's new solution is here, the controller and the sensor. Alot of the work is already done for you. It is a good thing to read over the controller, to think about some of the gotchas and other things to consider, whatever parts you finally end up utilizing.
http://www.home.agilent.com/USeng/nav/-536895276.0/pc.html

Another Agilent device, http://www.home.agilent.com/USeng/nav/-536895277.536905603/pd.html



Anyhow, since the SID show, a number of articles covering various aspects of LEDs and backlighting are hitting the street. Here is one:
http://powerelectronics.com/news/changes-led-backlighting/

wow...thanks for the links NewBie

No problem, any time rgbphil.