What’s the public’s understanding of LED lighting? It’s so very easy when writing about LED lights for the consumer market to get wrapped up in the numbers and acronyms: CRI of 80? Oh please, not good enough; 90 is better. Wait, CRI? Who measures light in CRI – that’s not good enough – you’ve got use include R7. No, R9! The lighting world starts to look like medieval scholars arguing about the number of angels that could dance on the head of a pin while ignoring the changes in civilization that had a more vital impact on the lay person’s spiritual well-being.
This was brought home to me last week when I got an email at 6:30 in the morning, asking if I’d like to be interviewed for a piece that Southern California public radio station KPCC was doing that morning on the newly introduced TW series LED bulb from Cree.
The way a radio interview works (I learned) is that you’re first interviewed by the program’s producer to find out what kind of questions should be asked during the show by the program host. Since the interview was triggered by the introduction of new Cree bulb, the producer started out by asking what was different about the TW series bulb. That’s easy, I thought: It has a high CRI. Most LED bulbs have a CRI of 80, which is the lowest CRI that’s acceptable to the consumer market. The new TW series Cree bulb has a CRI of 93, which is really quite good for a relatively inexpensive LED bulb: $20 from Home Depot.
What, said the producer, is CRI? Again, easy, I thought – color rendering index. Wait, I thought, I guess I have to explain that clearly and quickly. So, the color rendering index measures how colors appear when illuminated by the light – what general color they will be. Oh, she said, that’s like how you look under some lights that make you appear blue-ish. (Which was a reasonable conclusion from my description.) Well, no – that’s the color temperature of a light. A blue-ish light is what we call a cool white. Cheap fluorescent tube light can have color temperature of as high as 6000K or more; LED bulbs are a much warmer 2700K. Sunlight is a surprisingly cool 5000K. Wait, came the next question – isn’t warmer better? Why don’t we perceive sunlight as a “cool” white?
Ah, I said, finally seeing how to get myself out of the hole of confusion I’d dug, that’s because of the light quality of the sun, which is what CRI measures. White light means that all colors in the visible spectrum of light are present. (Is that common knowledge? I thought/hoped so.) The sun has a CRI of 100, which means that all of the different wavelengths of light – what we call colors – are equally present.
OK, relate that to the new Cree bulb, the producer requested.
Sure, I said brightly. No problem. See, LEDs are similar to CFLs in that the distribution of color wave isn’t even – there’s a big spike in the yellow wavelength, for most lighting-class LED components, for instance.
Wait, she said, you’ll need to define CFLs. I was pretty sure the producer knew that CFLs stood for compact fluorescent lights, but she wanted me to get away from all these acronyms I was using. And she was probably wondering why I was dragging yet another type of light into this interview, which was a good point: The average listener is probably not aware of the chip-on-the-shoulder the LED lighting industry has about poor light quality due to CFLs. The LED lighting community, on the other hand, lives in fear that the public’s first negative experience with energy-efficient lighting, the early CFLs, will tar LED lights with a black brush. But it’s likely the public has moved on.
So I instantly regretted bringing up CFLs.
Anyway, LEDs have a spike of greenish/yellowish light. Cree’s approach with its new TW (TrueWhite) series of bulbs was to add neodymium to the glass bulb that surrounds the LEDs. Neodymium acts as a notch filter, filtering out the excess yellows. It makes the light look rosier, and it’s especially appealing in skin tones.
In retrospect, I realized that if I had explained color temperature as a measurement of the color light appears as it strikes your eye, and color quality as being a measurement of how the light reflects off an object and what colors it picks up as it reflects, it might have been clearer.
After beating the subjects of color quality and color temperature to death, I realized how little known these topics are to the general public, and also, how difficult they are to explain. In general, people will not notice the difference unless they see two lights with different color temperature and quality right next to each other. This should probably be the golden law of lighting design – never position different lighting technology products so that they allow side-by-side comparisons. Even if you use two top-of-the-line lamps, the differences in their light will make for subtle changes that our extremely sensitive human eyes will pick up.
At this point, I explained why a high-CRI was important for the Cree bulb: The California Energy Commission (CEC) has developed a voluntary standard that requires LED bulbs to have a CRI of at least 90 to qualify as “California Quality. “ While the standard is voluntary, in order for a California utility to grant rebates for LED bulbs, the bulbs must meet the CEC standard.
The CEC standard also requires that the bulb’s R9 value is at least 70. It took me about 30 minutes to get across an understanding of color temperature and light quality – I also need to explain R9 values. I settled for saying that the R9 value specifically address red values in the light and is a measurement of how well the light renders red wavelengths.
We had now covered all the points the producer wanted to touch on. She wrapped up the conversation and said the show’s host would call me back in an hour for the actual interview, which would be taped, not live (hooray!). This left me an hour to stew on my poor explanations of light quality and temperature, and made me realize I needed a 30-second elevator pitch about what these light characteristics were. And if it had taken me 40 minutes to get the vital bits of information to the show producer, how would things fare with the show moderator, who was also presumably starting from scratch regarding light bulbs?
This is when I learned about the importance of the pre-interview by the show producer: She distilled our entire conversation down to about four questions that the show host asked. These four questions were:
- How much energy does this bulb uses compared to a traditional incandescent bulb?
- Can you tell us what neodymium is and how it affects light quality?
- Is high CRI something that the average human being would actually notice? Let’s say you put in one of these Cree bulbs in your kitchen — Is there a noticeable difference?
- Apparently there is some pricing help for consumers here in California. Can you tell us a bit about that? What amount will the rebate be?
These were excellent questions. In retrospect, they sound obvious, but not to a consumer-based audience that, when all is said an done, regards light as a commodity, and needs an explanation of why LED lighting can benefit them when it comes in an improved but more initially more expensive version.
Now that you know the background for this interview, and how hard I made the producer and moderator work, you can listen to the interview yourself at this URL: KPCC radio interviews Margery Conner about Cree’s high-CRI LED bulbs. (Click the blue “Play” button on the left under “Listen now.”) And many thanks for the efforts of the patient, thorough producer, Alexandra Woodruff, and the mentally-agile show host, Alex Cohen.