All conventional light sources modulate luminous flux to some degree, usually as a consequence of drawing power from AC 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 root mean square (rms) 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. In 2015, an Institute of Electrical and Electronics Engineers group published a recommended practice for evaluating flicker risks, which served as an excellent starting point, and ENERGY STAR® and California’s Title 20 are requiring the reporting of flicker performance and/or considering the adoption of flicker criteria. However, flicker metrics and criteria for different applications are not yet firmly established. 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. Fortunately, both the IES Testing Procedures Committee and International Commission on Illumination (CIE) Technical Committee 1-83: Visual Aspects of Time-Modulated Lighting Systems are close to finalizing test-measurement procedures.
THE PERFORMANCE OF FLICKER METERS
The growing awareness of flicker has led to a profusion of handheld flicker meters that have come on the market to help users determine in the field if flicker is occurring and, if so, whether the level is acceptable for the application in question. These handheld meters range from simple smartphone applications to scientific-grade meters. DOE has conducted two studies of flicker meters – one on the handheld variety and the other on benchtop models – to determine how they perform and to identify any issues.
- Characterizing Photometric Flicker: Handheld Meters
2018 Study documents the capabilities and accuracy of eight newly available handheld meters capable of measuring flicker in the field, compared to a reference benchtop meter.
- Characterizing Photometric Flicker
2016 Study compares three benchtop laboratory meters against a reference system to evaluate their performance and accelerate development of standard test and measurement procedures.
The increased availability of more-affordable and easier-to-use measurement devices in the previous two years reflects the growing awareness of flicker by lighting technology developers, and improved ability to address it through emerging measurement methods and recommended practices.
2018 Report: Characterizing Photometric Flicker: Handheld Meters
2016 Report: Characterizing Photometric Flicker
2013 Technology Fact Sheet: Flicker
2015 CALiPER Report 22.1: Photoelectric Performance of LED MR16 Lamps
2014 CALiPER Report 20.2: Dimming, Flicker, and Power Quality Characteristics of LED PAR38 Lamps
2013 CALiPER Exploratory Study: Recessed Troffer Lighting
2014 CALiPER Retail Lamps Study 3.1: Dimming, Flicker, and Power Quality Characteristics of LED A Lamps
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
1989 Journal Abstract: Fluorescent Lighting, Headaches and Eye-Strain
2015 International Electrotechnical Commission Technical Report 61547-1: Equipment for General Lighting Purposes - EMC Immunity Requirements - Part 1: An Objective Voltage Fluctuation Immunity Test Method