Light Flicker: A Reasonable Measurement Method in View
Meanwhile, there are some measuring devices to measure light flicker because it has been recognized that fluctuations in the brightness of artificial illumination have a negative effect on the nervous system of humans and other beings. Despite the years after recognizing the need to measure this, there is still no agreement on the measurement method. The only thing that is clear is that a simple amplitude measurement is not enough, but that an analysis and a weighted evaluation of the individual frequencies over a wide range is the right approach.
The most widespread method according to IES: RP-16-10 with %flicker (pure amplitude ratios) and flicker index (pure area ratios) is the least suitable because two values whose combination is not defined are not communicable and also frequencies not considered at all. Although IEEE 1789 only considers the main frequency, the weighting function contains a physiologically unexplained discontinuity. In addition, the limits are so sharp that even the low flicker of the European light bulb is considered dangerous. The procedure according to California Energy Commission Title 24 JA10 fails due to the lack of weighting of contained frequencies, which is why a highly noticeable flicker below 25 Hz is considered “low flicker”.
The procedure according to ASSIST includes only frequencies up to 70 Hz, thus stroboscopic and and phanto array effects are not considered.
The Compact Flicker Degree (CFD) continues to be the template for a way to measure, declare and assess light flicker, because the method provides a single percentage value for the entire human frequency range with frequency-dependent weighting and without definition gaps or discontinuities.
The CIE describes light flicker with the term “Temporal Light Artefact” (TLA) and proposes the PstLM method, which is not sufficient due to its low cut off frequency. Referred to NEMA 77 this is to be supplemented by the SVM procedure. Two values for the measurement of light flicker make the communication difficult and make a normative setting of application-specific limit values practically impossible. Suggestion: A clever combination of both values could make the TLA measurement useful.
This reduces the number of discussed approaches to basically only the two methods CFD or TLA, which are for the new European Ecodesign Directive up for discussion.