Visual Perception under Energy-Efficient Light Sources: Detection of the Stroboscopic Effect Under Low Levels of SVM

Temporal light modulation (TLM, known colloquially as “flicker”) of light sources has visual, neurobiological, and performance and cognition effects on viewers. This study aims to address an important gap in the scientific literature on the measurement of levels of TLM of light emitting diode (LED) light sources that may affect human health and productivity. The outcomes of this research are intended to assist decision makers when developing lighting policy measures and regulations. This study was initially proposed in response to a request for public comment on the draft European ecodesign regulation for lighting before a vote by the European Union (EU) member countries. An interim report was provided in December 2018, and those data were also presented at the CIE 29th Quadrennial Session in June 2019. This final report is based on a larger data set and contains a more detailed analysis of the subgroups. The International Electrotechnical Commission (IEC) and the Commission Internationale de l’Eclairage (CIE) have identified two metrics which may be measured and used to characterize lighting systems’ TLM: •PstLM, short term flicker metric for visible flicker at frequencies below 80 Hz, and •SVM, Stroboscopic Visibility Measure, for the higher frequency stroboscopic effect. Although the scientific development of these metrics and their associated measurement protocols continues, there is a parallel discussion concerning the appropriate levels of these metrics in regulations. At present there is limited public information concerning the occurrence of the stroboscopic effect under lamps of varying SVM values. To provide further information on levels of SVM, the IEA 4E SSL Annex commissioned this study to test the visibility of the stroboscopic effect for five levels of SVM (targeting values of 0, 0.4-0.6; 1; 1.6; and >2) using an experimental method similar to previous research from which the metric was developed. The preliminary report was based on a sample of 36 people across two sites (NRC in Canada and CSTB in France). This final report is based on data from 85 people (58 from Canada and 27 from France). The study focused on the effects on people under the age of ~30 because there is evidence that younger people may be more sensitive to TLM. The decision to place a limit on any metric involves three choices: (1) The acceptable frequency of the outcome occurring in the population; and (2) the acceptable proportion of the population who might experience this outcome; (3) whether there are sensitive individuals in the population, whose needs might be considered to have a higher priority over those who are less sensitive. These choices are value judgements that research can inform, but cannot determine. These data provide a first step towards discussions among stakeholder groups about suitable limits on lighting system TLM. The following guidance can be drawn from this work: •An SVM>2.0 caused virtually all of the participants to perceive stroboscopic effects of the rotating disk in every trial, and caused 50% of the participants to perceive stroboscopic effects of the metronome in 5 or more trials out of 8. •The proposed upper limit of SVM=1.6 is higher than the SVM for magnetic-ballasted T12 lamps {nema 2017}, which are known to cause headaches and eyestrain and to disrupt eye movements{wilkins veitch 2011}{veitch mccoll 1995}{wilkins 1986}. •25% of the people detected stroboscopic effects with the disk in 7 or more of the 8 trials (i.e., 88% detection), and 6 or more of the 8 trials (i.e., 75% detection) for the metronome at SVM=1.4 (75th percentile overall). The EU-28 population includes ~101 million people between the ages of 0-30. Based on the data presented here, SVM=1.6 would mean that on most of the occasions when they were exposed to that condition, one quarter of these 101 million young people could perceive the stroboscopic effect at greater than chance levels for both horizontal and vertical movement. •The 75th percentile detection rate dropped to 2 out of 8 trials (i.e., 25%) when the SVM was ~0.9. This is lower than the chance level of detection. •At SVM levels of 0.4 and below, the disc stroboscopic detection rate for the top quartile of the people dropped to 0. •Those in the population who are more at risk of visual stress (the top 30% of a measure of this risk) are more annoyed by an SVM of ~1.4 or greater than are those who are at low risk, even when the exposure is short (noting that long exposures were not included in this investigation).

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