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Troy, N.Y. -  6/1/2015

Measurement Procedure for Quantifying Perceptible Flicker Proposed in LRC's ASSIST recommends Publication

Flicker demonstration photoThe Alliance for Solid-State Illumination Systems and Technologies (ASSIST), a program of the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, has released a publication that proposes a new method of evaluating human perception of directly observed light source flicker. The publication, ASSIST recommends…Recommended Metric for Assessing the Direct Perception of Light Source Flicker, provides specific measurement procedures and calculations to objectively determine whether the amount of flicker from a light source is above or below the threshold of human perception. The metric is applicable to any waveform shape and frequency and is based on peer-reviewed laboratory and human factors experiments.

The increasing popularity of LED and solid-state lighting has led to a renewed interest in light source flicker and methods of evaluating the perception and acceptance of flicker. Compatibility of LED lamps with dimming circuits designed for incandescent lamps is an application of particular concern regarding flicker. Existing metrics, specifically percent flicker and flicker index, describe aspects of the physical waveform, says LRC senior research scientist Andrew Bierman, but do not relate it to human perception, nor do they include the frequency of the flicker, which is important to determining its perception.
“The purpose of the metric proposed is to accurately and objectively predict the perception of flicker for any lamp, regardless of its light output waveform or frequency,” said Bierman. Calculation of the metric starts with a relative light output waveform measurement and finishes with a single numerical result indicating whether the amount of flicker is above or below the threshold of human perception. Additionally, the result can be expressed as a probability of a viewer being able to detect flicker from a light source.
To validate the metric, 220 different waveforms were tested in a human factors experiment with 10 subjects to determine the flicker observation rate of each waveform and the metric’s ability to predict the observation. The metric also was used to predict the flicker perception of five previously untested commercial A-lamps. The flicker metric development and validation results are described in the paper, “A flicker perception metric,” which is now in press with Lighting Research and Technology journal (doi: 10.1177/1477153515581006).
Nadarajah Narendran, Ph.D., LRC director of research and organizer of the ASSIST program, notes that the goal of ASSIST’s proposed flicker metric is to give manufacturers a tool for evaluating their lamp designs for flicker. “The LRC and ASSIST’s industry members are interested in understanding flicker, its causes and solutions, and at what level it is detectable and acceptable to users,” said Dr. Narendran. He added that laboratories can easily create their own test setups based on this method to quantify the amount direct flicker produced by a light source.
The ASSIST recommends publication is available for free from the ASSIST website at To further show the metric calculation procedure, also included for download are several waveform examples that can be used with the sample Matlab code included in the publication’s appendices. Also available online are two previous flicker publications from ASSIST dealing with the perception of indirect flicker, also known as stroboscopic effects.
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 3M; Acuity Brands Lighting; Amerlux; BAE Systems; Bridgelux; Crouse-Hinds by Eaton; Cree; Dow Corning; Federal Aviation Administration; GE Lighting Solutions; Hubbell Lighting; Legrand; Lumileds; New York State Energy Research and Development Authority (NYSERDA); OSRAM SYLVANIA/OSRAM Opto Semiconductors; Philips Lighting; Samsung; Seoul Semiconductor; United States Environmental Protection Agency. Visit

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

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 conducts research in light and human health, transportation lighting and safety, solid-state lighting, energy efficiency, and plant health. 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. 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. Learn more at

About Rensselaer Polytechnic Institute
Founded in 1824, Rensselaer Polytechnic Institute is America's first technological research university. Rensselaer encompasses five schools, 32 research centers, more than 145 academic programs, and a dynamic community made up of more than 7,900 students and more than 100,000 living alumni. Rensselaer faculty and alumni include more than 145 National Academy members, six members of the National Inventors Hall of Fame, six National Medal of Technology winners, five National Medal of Science winners, and a Nobel Prize winner in Physics. With nearly 200 years of experience advancing scientific and technological knowledge, Rensselaer remains focused on addressing global challenges with a spirit of ingenuity and collaboration.