Cyberlux Corp (CYBL)

[analyzethis]

Nice article yesterday. Read Cyberlux'es PR's and patents and you see why CYBERLUX is a hidden, driving force in the industry:

http://www.solidstatelighting.net/lightimes/

RGB vs. Phosphor Similar to Digital vs. Analog
Tom Griffiths - Publisher
September 26, 2007...In reading the most recent US Department of Energy solid state lighting testing results, the footnote that the CIE color rendering index (CRI) on the RGB luminaires was correct at something like 14 suggested there was a knowledge gap that had just hit my personal radar scope. For those non-lighting folks giving a read, the CRI scale runs from 0 to 100. 100 is basically perfect sunlight, and 14 pretty much fails "the test" in a burly way. It doesn't mean they were bad, they just don't do well on the task a typical color rendering test measures. While it's not unreasonable to assume that most everyone in the lighting design industry is aware of the issues if they have spent any time with LED-based lighting systems, it seems a fair bet that not everyone has that experience yet. For that group, we'll see what we can learn together.

As everyone with a computer monitor or TV has experienced, red, green and blue can be combined to project any color the human eye can recognize. In a digital system, such as the computer monitor, the number of "bits" applied to the task of defining the color determines how many different colors can be represented or displayed. 8 bits gave us 256 colors, 16 gave us around 64000 and by the time we hit 24 bits, we are in the range of "true color", meaning that enough colors are displayed that our eyes pretty much accept it as "all the colors under the sun". The reality is that adds up to about 16 million, which amazingly still isn't perfect to the eye, but it is enough color steps to make it look real. Analog systems, such as our traditional color TV, pretty much have the ability to display every color as they are unconstrained by whole bit thing. The analogy would be to your rotary dimmer on an incandescent light, compared to a pair of up/down brightness switches that give you an incremental step. The rotary smoothly passes through every brightness level, while the digital version makes choppy steps up or down. Digital sound is the same way. The more bits the better, and by applying enough granularity it comes close enough to match an analog source, while adding the ability to control and filter things, as well as reproduce them time and again with zero quality loss. Our ears can be fooled pretty easily. Our eyes are amazingly sensitive to even the smallest steps, especially when they are combined across the red, green and blue color choices.

That's all about projecting a color, such as with that TV or computer monitor, or in the case of lighting, washing a wall or colorizing a fountain. Color rendering is something completely different, and is about reflecting color off of something, then back to our eyes. Bathing a building in one or more color tones doesn't carry much of an issue of color accuracy with it, just a color perception. The white LED "trick" is a great example of the projection versus perception point as they are most typically implemented by taking a pure-blue LED and shining it through a yellow phosphor. Some blue shines through, combining with the phosphor's yellow glow, and our eye sees white. The projection works. Once we shine it "at" something, we're into color rendering, and our eye isn't so easily fooled. The light suddenly appears bluish or yellowish and the colors of the items we're shining the light on aren't accurately represented to our eyes. (And for anyone over 40 out there, please raise your hand if the word "blue-ish" causes a flashback to Ringo's chat with the "blue meanies" in the Yelllow Submarine cartoon... Anyone?). As I understand it, the current CIE color rendering index was primarily designed as a means to test 1960's era fluorescent light sources in comparison to incandescent sources. At least one replacement has been suggested, but even with that "Color Quality Scale", an RGB solution only barely exceeds the "what color is my car?" performance of parking lot grade high pressure sodium and mercury vapor lamps.

Cool white LEDs tend to perform about like normal fluorescent sources, with CRIs in the range of 60-70 or so. Warm white LEDs project a broader spectrum and can get up into the 80-90 range, at the cost of efficiency (up to 40 percent fewer lumens per watt is not untypical). Making the same apparent white light with an RGB solution becomes a color quality nightmare, as the system, in a sense, has shifted from an "analog" to a "digital" one. The red, green and blue LEDs each project a fairly narrow spectrum, and that results in spectral gaps which hinder the ability to reflect or render the hues that make up our real world. Interestingly, RGB white solutions look great "on paper". Literally. Shining them at print images can give a great color rendering, since color printing also uses a 3 color "digital" scheme (cyan-magenta-yellow) that is designed to reflect back red, green and blue. RGB is essentially "digital light", while phosphor-based solutions are more "analog".

Understanding that provided an "aha" moment to connect to the benefit of combining white LEDs with red, green and/or blue ones for the dual purpose of better tuning the color temperature, as well as increasing the color rendering. Ingo Speier and Marc Salsbury of TIR Systems (now part of Philips Lighting) had a fairly comprehensive write-up on the issue from a SPIE conference available on TIR's website. That was a 2006 paper, so the referenced efficacies are a generation or two behind what we are seeing today, but the issues haven't changed. If you are washing a wall inside or outside a building, RGB is a great solution. Meanwhile, don't jump towards color-temperature or color-changing solutions for general illumination unless you know what's in it, or you might not like what comes out of it.

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