Evaluating The Flicker Caused By Lighting Products
Over the past year, reports have demonstrated that some SSL systems, particularly those paired with dimming controls, demonstrate significant photometric flicker, thought to cause photosensitive epilepsy, migraines, headaches, eye strain and non-specific malaise. Whilst the photobiological impact of flicker is still widely debated, the implications for image recording equipment are undeniably apparent and of increasing significance with the continued adoption of SSL in studio and stadium environments.
Definition and Sources of Flicker
Flicker is the term used for the rapid and repeated modulation of light output from a source. The principle source of flicker is the periodic variation in AC mains operated lamp output, at twice the AC frequency. Once an issue with fluorescent tubes with magnetic ballasts, flicker has largely been forgotten until recently, when the effect of SSL lamp drive circuitry and phase-cut dimming circuits have caused concern once again.
Potential Effects of Flicker
The health effects of flicker are generally divided into those due to visible flicker and those due to invisible flicker. In the visible domain, frequencies in the range ~3 to 70Hz represent a risk of seizure in those with photosensitive epilepsy, whilst in the invisible domain, at higher frequencies, migraines, headaches, eye strain and non-specific malaise may result.
Two metrics are currently defined for the evaluation of flicker, percent flicker, and flicker index, the latter being generally preferred since it takes account of difference in waveform shape or duty cycle. As standards for the evaluation of flicker are developed, account may also be taken of flicker frequency.
- ENERGY STAR® Method of Measurement for Light Source Flicker
- California Energy Commission Appendix JA10
- 1789-2015 - IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers
- UEFA Stadium Lighting Guide 2016
- CIBSE LG04 Lighting Guide 04: Sports Lighting - LG4
- ASSIST recommends…Recommended Metric for Assessing the Direct Perception of Light Source Flicker, Volume 11, Issue 3 (ASSIST 2015)