This report is the SSLC Platform’s Final Report on its international interlaboratory comparison (IC 2023) on the measurement of Temporal Light Modulation (TLM).
IC 2023 was designed to evaluate how consistently laboratories around the world measure TLM quantities, covering flicker and stroboscopic effects from LED lighting products. In addition, IC 2023 also served as a proficiency test for laboratories seeking accreditation. IC 2023 builds on the earlier SSL Annex Interlaboratory Comparisons (IC 2013 and IC 2017) and is the first to focus on the TLM quantities; short-term flicker indicator (PstLM) and stroboscopic effect visibility measure (SVM), as well as modulation depth, flicker index and perceptual modulation.
Key technical findings from IC 2023 include:
1) Overall proficiency performance of participating laboratories
2) Issues with laboratory uncertainty estimation
3) Large influence on PstLM measurements from AC power supplies
4) Issues with SVM measurements and TLM instruments
5) Large variability and conceptual issues with Mp
IC 2023 comprised two main parts and was supported by Nucleus Laboratories and Link Laboratories to ensure traceable Reference Values and to connect with regional projects:
Part 1: Lamp artefacts (Proficiency Test) used four commercially available LED lamps (ART-1 to ART-4) with different TLM characteristics. It was designed to comply with International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) 17043 so it can serve as a formal proficiency test for accreditation programmes. Nineteen “laboratories” (18 organisations, one with two setups) across 15 countries participated. KIEL served as Operational Nucleus Laboratory (pilot), with NIST, DTU, and NLTC as Supporting Nucleus Laboratories and EVERFINE and DTU as Link Laboratories. Reference Values were derived from measurements by the four Nucleus Laboratories.
Part 2: TLM waveform generator artefact (Technical Study) used a programmable TLM waveform generator (ART-5) with five custom designed waveforms to test instruments over a wider range of TLM conditions (high PstLM, high frequency PWM, multi-frequency waveforms, etc.) not readily found in the lamp models. Ten laboratories participated (subset of Part 1 participants). DTU served as Operational Nucleus Laboratory, with NIST, KIEL, and NLTC as Supporting Nucleus Laboratories. Reference Values were derived from measurements by the four Nucleus Laboratories.
IC 2023 was linked to two regional TLM measurement interlaboratory comparison projects: EMPIR “MetTLM” project in Europe; and China GBV-LC TLM measurement comparison. IC 2023 provided seasoned lamp artefacts and the measurement protocol to these two projects. Through these links, the IC 2023 Reference Values could be used to evaluate results from around 40–45 laboratories in total worldwide, giving a uniquely broad global picture of the state of TLM measurement.
The measurement rounds ran from 6 November 2023 to 25 April 2024 for Part 1 and from 6 December 2023 to 23 June 2025 for Part 2.
