Revision of <i>M</i> _P calculation method for flicker measurement

Direct flicker is a perception effect causing discomfort generated from lighting systems. While the short-term flicker indicator, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">st</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LM</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> , is most widely used, perceptual modulation ( M P ) is also a perception-based direct flicker metric used in many commercial instruments. However, M P values show substantial variation due to different starting phases of waveforms, caused by Fourier transform spectral leakage. Such variation was mostly removed by revising M P ’s calculation, applying a Hann window function and a correction factor to counteract the spectral broadening from the window when summing the DC-normalized spectral components. This approach is generalized to improve frequency-domain temporal light artefact metrics without loss of perceptual relevance when different windows are applied. To harmonize M P with direct flicker at a broader frequency range and viewing conditions eliciting higher direct flicker sensitivity, its original sensitivity curve (5 Hz to 65 Hz) is replaced by the one from Perz’s experiment, with a slight change of frequency range to 3 Hz to 80 Hz. With these improvements, M P,26 has been developed. A linear mixed-effects model is used to compare the different measurement conditions of M P,26 , providing guidance for recommended measurement conditions, i.e. measurement duration ≥5 s, sampling rate ≥2 kHz and a second-order anti-aliasing filter with cut-off frequency ≥400 Hz are recommended for robust result of M P,26 .