The U.S. Department of Energy (DOE) has released the findings of a new study on handheld flicker meters. Flicker – or, more precisely, temporal light modulation – is a repetitive variation in light output over a large frequency range, often exacerbated by relative eye or object movement. Flicker can have adverse effects on health and visual performance, as documented in a number of published studies and studied further through an Institute of Electrical and Electronics Engineers (IEEE) Standards Working Group. Therefore, the characterization of flicker, especially in the field, is important to ensure comfortable living and working conditions. The most commonly used metrics for quantifying flicker are Percent Flicker, Flicker Index, and Fundamental Flicker Frequency, although meters today also have the capability of measuring and reporting other flicker metrics.
The new study is a follow-up to a 2016 DOE study that compared three benchtop laboratory meters against a reference system. The benchtop meters from that study all measured light-intensity waveforms and calculated essential flicker-performance characteristics and metrics similarly, both to each other and to the reference system. The reference system was custom-built based on the available guidance at the time and found to produce consistent results to other flicker-testing apparatus in use at the time. Some differences in performance were found when the light-intensity waveforms had significant high-frequency content, and when proper configuration of the meters was not possible due to product limitations.
Today, more flicker meters are available, including more handheld meters that range from simple smartphone applications to scientific-grade meters. The new study compared the performance of eight handheld meters capable of measuring flicker in the field to a reference benchtop meter chosen based on its performance in the earlier study. A set of 12 light sources was selected for this study, based on their being typical of a specific architectural lighting product, exhibiting a specific waveform characteristic, and/or because they had previously been tested and were available for re-use in this study.
The study found that handheld flicker meters today are capable of providing performance nearing that of a benchtop meter in a controlled environment. Even free applications available for smart devices can provide a measurement that could be used as an indicator that a flicker problem may exist. However, the accuracy of the smart-phone-based application tested should be followed up by more-precise flicker measuring equipment, handheld or benchtop. Although the study uncovered some limitations and anomalies, these have been addressed in product literature, on the device or software itself, or through firmware/software updates.
Deviation of Percent Flicker for Handheld Meters (relative to reference meter measurement)
Deviation of Flicker Index for Handheld Meters (relative to reference meter measurement)
Mean Deviation (max levels)
Mean Deviation (dimmed levels)
The tables above present meter performance as it relates to Percent Flicker and Flicker Index, as well as the performance at maximum and dimmed light output levels across all light sources tested. See the full report for exact product model numbers and description of laboratory testing, as well as explanations on the limitations of some meters.
The test meters have qualities that vary in utility, which could have different benefits or downsides depending on the intended use of the meter. It is necessary to be aware of meter limitations that prohibit certain measurements from being reliable, e.g., some of the meters began to fail to detect flicker at much lower frequencies compared to other meters. Other aspects to consider for meter selection:
- Is there a need for other types of field measurements (light levels, color/spectrum, etc.)? Various meters tested have capabilities beyond the measurement of flicker, which makes them useful for other field measurements and evaluations.
- How will the meter physically be used? Some meters have sensors on the same side as the screen, others on the top edge, and others on detachable heads that allow measurements to occur remotely from the controller/body. One meter needs to be tethered to a computer to function. Knowing how testing will be done in the field is helpful in identifying whether a given meter would be a better option for the intended tasks.
- How will the data be used after the measurement is taken? And will light-intensity waveform data be useful or necessary? The waveform data may be used for calculating metrics that the meter does not automatically report or for calculating metrics that are developed in the future.
- Are formal reports needed? Some meters generate reports that may be used for recordkeeping or delivering to clients.
As flicker continues to be an important factor in the selection and use of lighting products, future flicker meters will enable design professionals and users in the field to adequately characterize lighting from a product or in a space and determine whether the level of flicker is acceptable for the given application.
1 Rider, Gene & Altkorn, R & Chen, Xiao & Wilkins, Arnold & Veitch, Jennifer & Poplawski, Michael. (2012). Risk assessment for LED lighting flicker. Injury Prevention. 18. A126-A127. 10.1136/injuryprev-2012-040590f.4.
Wilkins, Arnold & Veitch, Jennifer & Lehman, Brad. (2010). LED lighting flicker and potential health concerns: IEEE standard 2 2 PAR1789 update. 2010 IEEE Energy Conversion Congress and Exposition, ECCE 2010 - Proceedings. 171 - 178. 10.1109/ECCE.2010.5618050.