The lighting industry is ever-evolving, from the obsolescence of traditional lighting technologies to stricter energy codes and changes in the broader building industry. Researchers around the world are hard at work advancing understanding of human responses to light while developing new meters, software and lighting products. Yet the latest information often seems to live in a vacuum. Designers often read white papers and articles to track industry changes, but the design process is often not evolving fast enough to incorporate the latest research, best practices and technology.
The widespread adoption of LEDs has created a need for new test methods, tools and metrics, particularly relating light stimulus to human response. New questions have been raised regarding flicker, color perception and glare, along with other responses to light. The ability to tune the spectrum of light coincides with our emerging understanding of circadian rhythms and other biological responses to light with new metrics continuing to emerge.
With all these changes, one thing that has not evolved as quickly are the methods and metrics lighting designers use as tools to craft their designs. Why is this? For some perspective, two lighting designers befriended a lighting researcher and set out to evaluate four recently completed projects to better understand potential gaps that inevitably occur between current research and the reality of applying it in the design process.
- The first stop was a law firm in downtown Denver. The firm moved to a new office space in 2016 and at the time of installation was an early adopter of LED technology. LEDs are everywhere in the design, providing general office illumination to highlighting artwork and providing visual interest with a custom 3-story chandelier.
- The next two stops were Denver tech companies with all LED office spaces completed in 2019.
- The last stop was a Denver architecture firm with offices completed in 2008—in the not-so-distant days of fluorescent. The majority of buildings still have fluorescent luminaires, so this visit provided an important baseline.
These projects afforded a unique opportunity for conversations regarding the challenges in applying research, including LED lifetime, LED color, illuminance measurements and flicker.
There has been extensive testing of LED products over the past decade with specific requirements for predicting lifetime developed by the Il- luminating Engineering Society (IES) and approved by the American National Standards Institute (ANSI) detailed in ANSI/IES- LM-80 and ANSI/IES-TM-21.
Research continues to explore additional factors that may affect lifetime, such as cycling (turning off and on), along with other failure modes, such as color shift. Most manufacturers complete laboratory testing of their LED diodes for no more than 10,000 hours; these test results are used along with other information to estimate luminaire lifetimes.
Estimations of lifetime based on tests that are looking at limited information leave a lot of questions unanswered. How accurate are these estimations? What happens after 10,000 hours? It also leaves designers with little choice but to trust manufacturers.
Additionally, designers must figure out how to help owners understand that LEDs do not typically die; they just get dimmer with age.
Following project completion, lighting designers often support the project through contractual obligations and warranties for a few months up to a few years, but hardly any in the industry are doing additional follow up on the performance of LED products beyond a few years. Because of the incredible life of LEDs and because mainstream adoption of LEDs started around 2010, this hasn’t been an issue, but these questions are likely to start coming from previous clients as these systems age and approach end of life.
Along with research related to lifetime, there has been extensive focus on the color appearance and color-rendering properties of LED light sources. One major shift since the advent of LEDs is a new set of color-rendering metrics detailed in IES-TM-30-18, providing much more detailed information than the color rendering index (CRI). Researchers continue to focus on human color perception to better understand how particular LED light source spectral power distributions (SPDs) will be perceived, consumer preference, and communicating information about color rendering and light source color appearance.
Condensing how the human visual system processes SPDs, spanning 380 to 780 nm, into one number or even two meaningful numbers is very difficult. Our eyes are very good at white-balancing to different SPDs when transitioning between spaces and can also easily identify small differences in SPDs when light sources are side by side. The SPDs of LEDs shift over time, but if everything shifts together it is difficult to notice. The problem of replacing a failed LED product after several years is one of the reasons why researchers continue to focus on LED SPD shift over time.
Ideally, all possible lighting issues would be figured out during design or fixed during construction with all products arriving to the job site around the same time. When replacements or additions to lighting systems need to occur, there can be a noticeable color variation between older and newer products.