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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.


In February 2016, DOE published a report on the performance of three emerging flicker meters. The purpose of the study was to help specifiers determine the flicker behavior of lighting products, and to accelerate the development of standard test and measurement procedures. The results and analysis show that the commercial meters measured light-intensity waveforms and calculated essential flicker performance characteristics and metrics similarly, both to each other and to a reference photoelectric characterization system. Some differences in performance were found, however, when measurements were taken of light-intensity waveforms with significant high-frequency content greater than the dominant 120 Hz found in many products at full output. If the meter was not appropriately configured, or if proper configuration was not possible given meter constraints, then the waveform characteristics were not accurately captured, often resulting in the calculation of flicker metrics that deviated significantly from the reference.

Metrics and Test Methods


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

IEEE Standard 1789-2015: IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers

2010 Conference Abstract: LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update

1989 Journal Abstract: Fluorescent Lighting, Headaches and Eye-Strain

1995 Journal Article: Modulation of Fluorescent Light: Flicker Rate and Light Source Effects on Visual Performance and Visual Comfort

2012 Report: ASSIST Recommends… Flicker Parameters for Reducing Stroboscopic Effects from Solid-State Lighting Systems

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

2014 Presentation: Objective Testing of Flicker and Stroboscopic Effects Resulting from Mains Voltage Fluctuations

2014 Journal Article: Modeling the Visibility of the Stroboscopic Effect Occurring in Temporally Modulated Light Systems