LRC Calculates Acceptability of LED Flicker
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), particularly where dimming is implemented. The lighting 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.
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.
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 perceived 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 Narendran.
The ASSIST recommends publication is available for free download on the ASSIST website at www.lrc.rpi.edu/programs/solidstate/assist/recommends/flicker.asp.
The published studies leading to the ASSIST recommendation can be found online (subscription or access required). 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 & 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 and the LRC
In August 2012, the Lighting Research Center at Rensselaer celebrated the 10th anniversary of the Alliance for Solid-State Illumination Systems and Technologies (ASSIST). The program was established 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 several leading lighting companies and organizations.
ASSIST recommends is a publication program of the Alliance 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 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.
The Lighting Research Center (LRC) is part of Rensselaer Polytechnic Institute of Troy, N.Y., and is the leading university-based research center devoted to lighting. The LRC offers the world’s premier graduate education in lighting, including 1- and 2-year master’s programs and a PhD program. Since 1988 the LRC has built an international reputation as a reliable source for objective information about lighting technologies, applications, and products. The LRC also provides training programs for government agencies, utilities, contractors, lighting designers, and other lighting professionals.
Rensselaer Polytechnic Institute, founded in 1824, is the nation’s oldest technological university. The university offers bachelor’s, master’s, and doctoral degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of fields, with particular emphasis in biotechnology, nanotechnology, information technology, and the media arts and technology. The Institute is well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.
Source: www.lrc.rpi.edu