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Troy, N.Y. -  8/20/2012

Calculation methods for estimating detection and acceptance of LED light source flicker published in ASSIST recommends

Flicker demonstration photo; click for larger image

Both photographs above were taken under a flickering light source (at 120 Hz) with an exposure time of 1/15th of a second. In the top photograph, the ruler is stationary and no stroboscopic effects are seen. In the other photograph, multiple images are produced by each flicker cycle as the ruler moves across the scene.

The Alliance for Solid-State Illumination Systems and Technologies (ASSIST) recently released a new publication that addresses the issue of LED light source flicker. The publication, ASSIST recommends… Flicker parameters for reducing stroboscopic effects from solid-state lighting systems, provides calculation methods for estimating the detectability and acceptability of stroboscopic effects from flicker using the parameters of frequency and percent flicker. The calculation methods are based on Lighting Research Center (LRC) work published last year in Lighting Research & Technology journal.
 
Flicker and stroboscopic effects have been a concern with solid-state lighting (SSL), and industry and the ENERGY STAR program have debated the effects of frequency and other driving modes on the perception and acceptability of flicker. To provide further data and guidance in this area, ASSIST funded human factors studies of indirect flicker perception. The studies, led by LRC senior research scientist John Bullough, were designed to determine what light source parameters affect the detection of flicker and stroboscopic effects, and to assess subjective responses to flicker in terms of acceptance and comfort. Previous research had shown at what frequencies direct flicker is perceptible but did not identify thresholds and acceptance levels for indirect perception, nor a means of predicting these levels for SSL.
 
The results from these studies suggest that there is a tradeoff between the frequency and the modulation depth in the detection and acceptability of indirect flicker. Follow-up studies systematically evaluated this tradeoff and looked more closely at the relationship between frequency and percent flicker. The conclusions drawn from these studies led to the development of the calculation methods detailed in the ASSIST recommends publication, which provides estimations of the detection and acceptability of light source flicker for a given frequency and percent flicker.
 
Nadarajah Narendran, LRC director of research and organizer of the ASSIST program, notes that the methods offered can be used easily by LED lighting manufacturers to develop systems that minimize the effects of flicker. “For the past 10 years, the LRC and ASSIST’s industry members have investigated the technical problems impeding market acceptance of LED lighting. This is one example of the work that ASSIST is doing to provide the industry with solutions that can be implemented quickly and effectively,” said Dr. Narendran.
 
The ASSIST recommends publication is available on the ASSIST website at http://www.lrc.rpi.edu/programs/solidstate/assist/recommends/flicker.asp. The published studies leading to the ASSIST recommendation can be found online. The first paper, “Effects of flicker characteristics from solid-state lighting on detection, acceptability and comfort,” was published last year in volume 43, issue 3, of Lighting Research and Technology. The second paper, “Detection and acceptability of stroboscopic effects from flicker,” is published in the online early access section of the same journal.
 
About ASSIST
The Alliance for Solid-State Illumination Systems and Technologies (ASSIST) was established in 2002 by the Lighting Research Center as a collaboration between researchers, manufacturers, and government organizations. ASSIST’s mission is to enable the broad adoption of solid-state lighting by providing factual information based on applied research and by visualizing future applications. The Lighting Research Center conducts research, demonstration, and educational activities on behalf of ASSIST. ASSIST is sponsored by Acuity Brands Lighting; Amerlux Global Lighting Solutions; Bridgelux; Cirrus Logic; Cooper Industries; Cree; Dow Corning; Federal Aviation Administration; GE Lighting Solutions; ITRI, Industrial Technology Research Institute; Intematix Corp.; LG Electronics; LG Innotek; Lighting Science Group; Lite-On; New York State Energy Research and Development Authority (NYSERDA); OSRAM SYLVANIA/OSRAM Opto Semiconductors; Philips Lighting; POSCO LED; Sharp Laboratories of America; Seoul Semiconductor; Toshiba; United States Environmental Protection Agency; WAC Lighting; WattStopper.
 
About ASSIST recommends
ASSIST recommends is a publication program of the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) that offers formal recommendations to the LED and lighting communities about issues important for the reliable performance of LED lighting and its comparison to other light source technologies. The first ASSIST recommends publication in 2005 provided a definition and method for estimating the useful life of LED lighting, which later became the basis for the Illuminating Engineering Society’s LED lumen maintenance standard, known as LM-80. The publications available include recommended definitions, testing and measurement methods, calculation methods, and best practices. All ASSIST recommends publications can be downloaded for free at www.lrc.rpi.edu/programs/solidstate/assist/recommends.asp

About the Lighting Research Center
The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute is the world's leading center for lighting research and education. Established in 1988 by the New York State Energy Research and Development Authority (NYSERDA), the LRC has been pioneering research in solid-state lighting, light and health, transportation lighting and safety, and energy efficiency for nearly 30 years. LRC lighting scientists with multidisciplinary expertise in research, technology, design, and human factors, collaborate with a global network of leading manufacturers and government agencies, developing innovative lighting solutions for projects that range from the Boeing 787 Dreamliner to U.S. Navy submarines to hospital neonatal intensive-care units. LRC researchers conduct independent, third-party testing of lighting products in the LRC's state of the art photometric laboratories, the only university lighting laboratories accredited by the National Voluntary Laboratory Accreditation Program (NVLAP Lab Code: 200480-0). In 1990, the LRC became the first university research center to offer graduate degrees in lighting and today, offers a M.S. in lighting and a Ph.D. to educate future leaders in lighting. With 35 full-time faculty and staff, 15 graduate students, and a 30,000 sq. ft. laboratory space, the LRC is the largest university-based lighting research and education organization in the world.

About Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute, founded in 1824, is America’s first technological research university. The university offers bachelor’s, master’s, and doctoral degrees in engineering; the sciences; information technology and web sciences; architecture; management; and the arts, humanities, and social sciences. Rensselaer faculty advance research in a wide range of fields, with an emphasis on biotechnology, nanotechnology, computational science and engineering, data science, and the media arts and technology. The Institute has an established record of success in the transfer of technology from the laboratory to the marketplace, fulfilling its founding mission of applying science “to the common purposes of life.”