Over the past year, reports have shown that certain SSL systems, especially those coupled with dimming controls, exhibit considerable photometric flicker, believed to cause non-specific malaise, eye strain, headaches, migraines, and photosensitive epilepsy. While the photobiological impact of flicker is still extensively debated, the implications for image recording equipment are absolutely evident and of increasing importance with the continued adoption of SSL in stadium and studio environments.
Definition and Sources of Flicker
Flicker refers to the rapid and repeated modulation of light output from a source. The main source of flicker is the periodic variation in AC mains operated lamp output, two times the AC frequency. Flicker, which was once a problem with fluorescent tubes with magnetic ballasts, has largely been forgotten until recently, when the effect of phase-cut dimming circuits and SSL lamp drive circuitry have caused concern once again.
Potential Effects of Flicker
The health effects of flicker are typically divided into those caused by invisible flicker and those caused by visible flicker. In the visible domain, frequencies in the range ~3 to 70 Hz signify a risk of seizure in those with photosensitive epilepsy, while in the invisible domain, at higher frequencies, non-specific malaise, eye strain, headaches, and migraines are some of the possible consequences.
Presently, two metrics are defined for the evaluation of flicker – flicker index and percent flicker. Flicker index is usually preferred as it takes account of the difference in duty cycle or waveform shape. As standards for the evaluation of flicker are developed, flicker frequency may also be considered.
This information has been sourced, reviewed and adapted from materials provided by Bentham Instruments Limited.
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