All conventional light sources modulate luminous flux and intensity to some degree, usually as a consequence of drawing power from AC mains sources. Many terms are used when referring to this time variation, including “flicker,” “flutter,” and “shimmer.” The Illuminating Engineering Society of North America (IES) Lighting Handbook defines flicker as “the rapid variation in light source intensity.” The periodic waveform that usually characterizes flicker can be principally described by four parameters: its amplitude modulation (i.e., the difference between its maximum and minimum levels over a periodic cycle), its average value over a periodic cycle (also called the DC component), its shape or duty cycle (the ratio between the pulse duration and the period of a rectangular waveform), and its periodic frequency (i.e., the number of recurring cycles per second).
Flicker is garnering increasing attention from lighting designers and specifiers, the standards and specification community, and, consequently, lighting manufacturers. An Institute of Electrical and Electronics Engineers group has developed a recommended practice for evaluating flicker risks, and ENERGY STAR® and California’s Title 20 are requiring the reporting of flicker performance and/or considering the adoption of flicker criteria. Some manufacturers appear to be giving flicker increased design priority, as evidenced by the improved performance of new product generations.
An understanding of why flicker matters and how much it varies across commercially available products is increasingly becoming essential to proper lighting design. Specifying the right product for a given application and risk sensitivity further requires the ability to quantitatively characterize flicker. At this time, however, there is no standardized test procedure for measuring photometric flicker from light sources, and manufacturers rarely report flicker characteristics.
Ideally, a test and measurement procedure would facilitate the capture of light-source intensity or luminance over time and potentially describe how to characterize periodic waveform characteristics (e.g., amplitude modulation, shape or duty cycle, frequency) using one or more metrics, and how to identify aperiodic characteristics. Both the IES Testing Procedures Committee and International Commission on Illumination (CIE) Technical Committee 1-83: Visual Aspects of Time-Modulated Lighting Systems are considering the development of standardized test and measurement procedures for flicker.
THE PERFORMANCE OF FLICKER METERS
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2013 Technology Fact Sheet: Flicker
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2014 CALiPER Report 20.2: Dimming, Flicker, and Power Quality Characteristics of LED PAR38 Lamps
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2012 Presentation: LED Dimming: What You Need to Know
2014 Presentation: SSL Flicker Fundamentals and Why We Care
2015 Presentation: Flicker: Understanding the New IEEE Recommended Practice
2010 Conference Abstract: LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update
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