Championing the design and application of LED light sources
The Fifth Annual LEDucation conference, presented by The Designers Lighting Forum of New York (DLFNY) with the support of the New York Section of the Illuminating Engineering Society (IESNA), held on March 16, 2011, at the Hotel Pennsylvania, brought lighting industry professionals up to date on solid-state light sources and controls. The meeting offered several seminars and an exhibit area with more than 90 manufacturers and distributors showing their products and services throughout the afternoon and evening sessions.
With the U. S. Department of Energy (DOE) serving as a central player in collaborating with manufacturers, allied trade associations, professional lighting designers, and standards-making bodies, LED technology is on a continuous track of advancement. Because LED development is getting most of the R&D funding, it’s no surprise that new LED products are being introduced at more than 10 times the rate of all other light sources combined. As a result, specifiers want to know about reductions in cost per lumen, gaining greater consistency in color control, and achieving reliable control methods with LED equipment. Following is a short recap on two of the seminars presented at this event.
Michael Myer, a lighting engineer with Pacific Northwest National Laboratory (PNNL), Richland, Wash., reviewed two of the most important solid-state lighting standards in his "LED Standards Update" presentation. IESNA LM-79 "Approved Method for the Electrical and Photometric Testing of Solid-State Lighting Devices" specifies a method for measuring the photometric and electrical properties of these sources in order to compare light output and calculate luminaire efficiency. IESNA LM-80 "Approved Method for Measuring Lumen Depreciation of LED Light Sources" sets up procedures at the chip level for measuring the reduction in light output over time. He also noted the industry can look forward to the development of a new binning standard in the near future, as well as the introduction of a new term, “color consistency deviation,” because the output of LEDs differs from all other light sources, regarding color consistency and color shift over time.
In his presentation "The Color of White," Ron Steen of Xicato in Silicon Valley, Calif., reiterated that color is a major concern for solid-state lighting and the two metrics used to describe the color characteristics of white light — correlated color temperature (CCT) and color rendering index (CRI) — are not fully adequate for evaluating these new sources. CRI was developed in 1975 to help characterize light typically produced by incandescent bulbs. Work is currently underway to create a new metric, called color quality scale (CQS), which uses a different and larger set of test colors. In addition, CQS does not penalize a light source that increases color saturation slightly and leans toward human color preferences. Because of the wide use of a blue LED chip source and yellow phosphors to create a white light source — coupled with the fact that color stability depends on the phosphors and the thermal management system used — the light output of the high power LED source upsets the concept of what a color point is on a CIE color chart and how to define color maintenance. For that reason, new color space evaluations are under development.