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We all know that LED technology is advancing rapidly and that currently, it is the way to go for most lighting applications. However, lighting experts familiar with traditional lighting methodologies need a new bag of tools to make the inevitable change to solid state lighting. We need to equip them with these tools sooner rather than later so that they can be effective in their roles. Soome food for thought.
1. Color temperature or correlated color temperature is no longer meaningful unless it is related to the Planckian locus.
2. LEDs do not reproduce colors in the same way as conventional lighting. How do we work with CRI? How is it calculated for LEDs? And how do we differentate between lights that profess the same specs but which we can see with our eyes have different hues?
3. How do we understand spectral power diagrams as they relate to LEDs?
4. Solid state lighting brings a new dimension in color changing and control. How do we take advantage of these?
5 What is the story with "pupil lumens" as opposed to lumens which we read on our meters?
6. What do we need to know about thermal management, color shifting and longevity?
This is just a start!
Comments please.

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Replies to This Discussion

Hello Les, great questions.
If you don't mind I will post your questions in other forums to see if we can find answers that I will post here later.
Hi Alex:
I believe that I have the answers to the questions! However, we as professionals in LEDs need to educate the market including designers, manufacturers etc., that LED technology is different from what they are used to and that they need new tools to evaluate LED alternatives. We offer workshops on these and other topics related to LED technology and color. Let me know if I can help in any way.
Regards,
Les
I found this to be an interesting read on the subject.

http://www.mikewoodconsulting.com/articles/Protocol%20Fall%202008%2...
Bill Cronheim said:
I found this to be an interesting read on the subject.

http://www.mikewoodconsulting.com/articles/Protocol%20Fall%202008%2...
Bill Cronheim said:
I found this to be an interesting read on the subject.

http://www.mikewoodconsulting.com/articles/Protocol%20Fall%202008%2...

Hi Bill:
Thanks for the comment. One really has to understand LEDs and color to get the most out of them. Are you involved in stage lighting? One of the largest Chinese manufacturers has asked us to prepare a workshop on LEDs and stage lighting. Would this be of interest to you? We believe that the color-changing methodology and control available in working with solid state lighting will lead to adoption of LEDs in stage lighting. Just for your information, we are working on LED spotlights which could be used in stage lighting.
Regards
Les
Hi Les,

Yes please. Keep me informed.
Bill Cronheim said:
Hi Les,

Yes please. Keep me informed.

Will Do!
Thanks
I think something that could be improved with LED's and would be reall great in theaters, Is using the same type of led that high end uses in thier products. Because you know when you have the RGB LEDS , when it hits something you can see the RGB colors on the outline of it. Just an idea but I think it would be really cool like if color kinetics were to use those leds for their products.
Hi Cody:
I am not sure what you mean by "high end" LEDs. If you mean high CRI LEDs, you need to study their spectral power distributions very carefully to see if they cover the full visible spectrum well. Also, you need to examine the way CRI is calculated. Because it is an average, and averages can be confusing, you need to look at the performance from R1 through R14 and especially at R9 which is red.
Hope this helps!
Les
Hello Les and everybody,
I posted your question in another forum and this answer from Zanne N seems interesting:

Reply by Zanne N on July 10, 2009 at 9:11pm

From what I've learned, calculating CRI without the right equipment (an integrating sphere) is hard... First you need to find the color temperature and CIE coordinates. Then you have to shine the light source onto very specifically(and expensive and hard to find) colored cards and record the amount of light reflected. Normalize those numbers onto a special chart, then math happens and you get the CRI :).. I used a spectrometer to find the color temperature and CIE coordinates of my quantum dots but have not figured a way to get accurate results for CRI.. But if you have an integrating sphere I'm almost positive it can find the CRI for you... Please correct me if something is wrong but this is how I understand it..

Oh and one more thing, you can't compare CRI with two lights of different color temperatures.. A 10k light source could have a CRI of 100 and look completely different than a 3200 K light source from an incandescent (which is a 100 CRI black body radiator).. This gets into spectral power distribution...

Anyways, I think we should just aim for high CRI phosphors and such.. Nobody wants to look like they are living dead in the house..

Cheers,

AC
I have to add to this conversation that last February in a LED convention in Santa Clara, a data table just like the one called "nutrition facts" that comes with food products was shown to us as a solution, of course, instead of Calories and Sugar, had Wattage, Life in hours, Lumens/Watt, little color spectrum bar to show the color temperature...

The HB LED lighting industry is working in creating very much needed standards
Hi Alex:
I have seen many data tables, but have found most of them to be deficient in one way or another. The way calculations are made makes a difference. As mentioned before, color temperature is not meaningful without coordinates or a positioning relative to the Planckian locus. CRI is an average and also the formulae used in calculations differ. As Zanne N. mentions above, you really need a sophisticated, calibrated system with an integrating sphere to make measurements, and then you have to look at the numbers through the spectrum and not just at an average. NIST and others are working on a Color Quality Standard [CQS] for LEDS, but I personally think it misses the mark because it has no bright red which is the biggest problem with LEDs.

Standards are of course very important, but with LEDs, measurement for compliance is just as important. Production units often differ from the samples supplied to labs for metrology, so one needs to view specs in perspective. I have learned to "trust my eyes" when I check products, or do my own independent tests.

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