The Department of Energy has issued a new report on lessons learned as a market for solid-state lighting develops. The lessons mostly have the character of things that need improvement.
The authors of the report, "Solid-State Lighting: Early Lessons Learned on the Way to Market," say that they selected lessons where "useful information can be applied going forward." In other words, this is not an account of solved problems.
The sidebar lists all 12 lessons in the report's language. I would like to touch on a few nuances and implications that struck me while reading through the 47 pages of lessons.
A lifetime of control
Lesson 2 states that LED lifetime and reliability cannot be exactly predicted. The report notes that the presence and growing importance of lighting controls compounds this problem into intractability. The standard testing that is used today to try to extrapolate luminaire lifetime assumes that conditions are static when the luminaire is in use. Controls allow the level of light, and perhaps other variables such as color or CCT, to be set over wide ranges. There is no theoretical basis for assuming what the effect of running a luminaire at 50% light output will be on a product's lifetime, let alone extrapolating to arbitrary levels of light output over time.
Lesson 3 notes that, while specifiers prefer complete families of lighting products, manufacturers have a difficult time meeting that desire due to the rapid evolution of technology. One fallout of this situation is that, since specifiers cannot necessarily find the variety of products needed for a project offered by a single manufacturer, they may mix and match luminaires from different suppliers. The result is often mismatched color (even for products nominally having the same CCT), disparate rates of lumen degradation and color shift, and an inability easily to stock replacement parts.
Another factor mitigating against manufacturers' ability to offer complete product families is the burden imposed by combinatorial product testing, as Lesson 1 details.
Lesson 4 touches on a topic we have examined here recently, some LED makers are exploring ways to narrow the color variation in the binning they offer -- indeed this has been going on for some time. Lesson 4 notes that color has become a point of confusion among consumers in the SSL era. Among the report's recommendations for remedying this situation: "Standards organizations should consider establishing tighter tolerances for chromaticity bins to reduce product-to-product variability at the same CCT."
Lesson 5 involves the color shifts that many luminaires experience over their lifetimes. There are no agreed-upon standards to characterize this behavior and no way now to communicate it to consumers. Thus it is not surprising that manufacturers' warranties rarely if ever mention guarantees of color stability. As we discussed last November, this issue is a sleeper that could cause the public to sour on SSL as its true dimensions become more widely known. Standards describing and circumscribing color shift are sorely needed.
The DOE's report is packed with such insights into, and implications of, the issues the SSL industry faces today. It is recommended reading.
— Keith Dawson , Editor-in-Chief, All LED Lighting