Temporal light modulation: Data processing and metric calculations

Abstract

There are multiple metrics used in research and industry to describe the visibility of temporal light modulation (TLM), colloquially referred to as ‘flicker’. However, the metrics are not straightforward to calculate, and the values sometimes vary according to sampling rates. This work addresses the vagaries in processing TLM waveform data and calculating the metrics. For each TLM metric, its sensitivity to sampling rate is presented, followed by recommendations for improving the reliability and consistency of calculated metrics. Appropriate sampling rates are proposed according to the nature of the waveform and metric. The analyses of this paper are based on ideal waveforms without noise or instability, but the effects of sampling rate also apply to real-world waveforms. Some metrics, such as the Stroboscopic Visibility Measure, were relatively stable (i.e. produced the same value regardless of sampling rate) – within the ranges for which they are defined – for sinusoidal and/or rectangular TLM waveforms. In contrast, short-term flicker indicator $\left(P_{\mathrm{st}}^{\mathrm{LM}}\right)$ and perceived modulation $\left(M_{\mathrm{P}}\right)$ values exhibited greater variability based on sampling rate. Metric values from sinusoidal waveforms were generally more stable than those from rectangular waveforms, although $P_{\mathrm{st}}^{\mathrm{LM}}$ showed inconsistency even with sinusoidal TLM.