LED Lighting CRI and the Lighting Revolution

February 29, 2008

We have mentioned this many times in previous articles, but it’s worth pointing out again here: incandescent lighting is old technology. We live in an age of super-powerful computers that fit in the palms of our hands, but most of the world still lights its environment with archaic and inefficient incandescent lighting technology. Given the extraordinary benefits of compact fluorescent lighting, which is readily available to the consumer market, it is difficult to understand why CFL technology hasn’t completely replaced the incandescent light. Many have speculated that this is a result of the strength of the utility industries, who would stand to lose substantial revenue. Even if this is true to some extent, it certainly hasn’t kept CFL out of the supermarkets. In any case, it would be futile for the utility industry to try and suppress this technology, in light of recent legislation by the U.S. and other countries, that will effectively outlaw new sales of the inefficient incandescent lighting in the next 5 years or so. It turns out, that the real obstacle preventing new lighting technologies such as CFL and LED from gaining wide spread acceptance, has to do with light quality.

I am not very sensitive to this, but many people are. In fact, my mother replaced all of the lights in her kitchen with CFLs, but removed them in about a week. She said she didn’t like the color. I didn’t notice much of a difference. To my surprise, my mother is not a freak. Apparently, many people feel the same way she does about the light quality produced by CFLs, which is not as good as the light produced by traditional incandescent bulbs.

Light quality is measured using a scale called the Color Rendering Index (CRI). The CRI of a light source, is a measurement of the lights ability to accurately reproduce the true colors of various objects. An objects “true color”, is determined by comparing it to an ideal or natural light source. Light sources with a higher CRI, say 90 or above are consider quality light sources, and anything below that is simply not easy on the eyes.

According to a recent article in Forbes on the issue, CFLs have a CRI of about 70. We don’t sell CFLs so I don’t know a lot about the industry, but I think CFLs with CRIs in the low to mid 80s are common. In any case, this is still not a high quality light source. The point made by the author of the Forbes article is that the light quality of CFLs is a major reason that the new lighting technology isn’t already in every U.S. home.

Unlike CFLs, some claim that LED technology is achieving CRIs of 92 or more, and the results keep improving. If this proves to be true, the implication is that LED technology would be on a path to essentially leap-frog CFL lamps, into the lead as the future of lighting. However, some researchers believe that the CRI, simply cannot be applied to white LED light. The International Commission on Ilumination’s (CIE) study on the issue, determined that the CRI is not useful to predict the color rendering of an LED light source. The CIE’s study notes that the CRI index is tied too closely to the incandescent light to be useful. (In fact, the CRI essentially uses the light produced by the incandescent lamp as the standard.) New research is showing that light produced by LEDs (and even CFLs), that has a very low CRI, are actually very visually appealing to the human eye. This phenomenon was actually first demonstrated with the latest advances in incandescent technology. GE and other companies began producing “daylight” incandescent lights. The light produced by these lamps only had a CRI of around 80, but objects illuminated by the light appeared livelier and brighter, than those illuminated by an incandescent light source with a high CRI.

The significance of the CIE research, isn’t a conclusion that LEDs or other new lighting technologies can’t produce high CRIs: the importance of this study is that the CRI, like the light for which it was developed to measure, may be obsolete.