Interlaboratory Comparison 2023 (IC 2023) for Temporal Light Modulation (TLM) measurement
The SSL Annex launched its 2023 Interlaboratory Comparison (IC 2023) of temporal light modulation (TLM) measurements in September 2023, issuing three Official Announcement Letters in English, Japanese and Korean. IC 2023 was open to all photometric labs able to measure TLM quantities of LED lighting products, in particular, short-term flicker indicator (PstLM), and stroboscopic effect visibility measure (SVM). This comparison was organised primarily to investigate the degree of agreement in the measurements of these TLM quantities among the participants both as a technical study as well as to provide verification of each participating laboratory’s measurement capabilities.
IC 2023 was designed in compliance with ISO/IEC 17043 to serve as a proficiency test for SSL testing accreditation programmes that recognise this comparison, as was done in the SSL Annex’s IC 2013 and IC 2017. IC 2023 will use IEC TR 61547-1 and IEC TR 63158 as the test methods for determining quantities PstLM and SVM respectively. If recognised by accreditation bodies, the participant results reports may be used as a proficiency test for IEC TR 61547-1, IEC TR 63158 and regional versions of these test methods. The results can also be used for benchmarking.
Participating laboratories were shipped a set of four non-directional LED lamps for testing PstLM, SVM, and optionally, flicker index, Mp, and other quantities. Participants were also able to choose to participate in an optional Technical Study where they will be sent (separately) a light waveform generator with five programmed specific waveforms for measurement, which may be useful to analyse possible problems in participants’ measurements.
To make IC 2023 widely useful, this IC will be linked with EMPIR MetTLM project, which will conduct an interlaboratory comparison of measurement of TLM which, among their artefacts, will includes the same artefacts as IC 2023 and using nearly the same Technical Protocol. In addition, this IC will also be linked to China GBV-LC TLM, which is organised by National Lighting Test Centre (Beijing, China) for participants within China for measurement of TLM. Both of these regional ICs have appointed Link Laboratories that will participate in the IC 2023 Nucleus Laboratory Comparison to establish links to the reference values in IC 2023.
Prior to IC 2023 measurement rounds, a Nucleus Laboratory Comparison (NLC) was conducted to verify measurement agreement among the five Nucleus Laboratories and to establish reference values for artefacts as well as linking scales for the Link Laboratories. Figure 1 illustrates the structure of IC 2023. The NLC (red circle) was conducted first to compare measurements by the two Operational Nucleus Laboratories, the three Supporting Nucleus Laboratories and the three Link Laboratories (two of which are also serving as Supporting Nucleus Laboratories). The NLC established the reference values for IC 2023 main round (black circle) and the linking data for the two regional comparisons (blue and purple circles).
Figure 1. IC 2023 structure, with Nucleus Lab Comparison (red circle), measurement round (black circle) and two linked regional comparisons (blue and purple circles)
IC 2023 lamp artefact (ART-1 to 4) measurement rounds will be conducted as bilateral comparisons (a star-type comparison) between each participating laboratory and the Operational Nucleus Laboratory. The optional IC 2023 technical study using a wave-form generator (ART-5) will be conducted as a modified star-type comparison, where one generator is shared with two participants between each Operational Nucleus Lab measurement.
The SSL Annex published the Technical Protocol for IC 2023 which describes the details of the comparison artefacts (four LED lamps and a TLM generator), as well as the TLM quantities to the measured and the measurement conditions. Registration was open from 25 September to 31 December 2023. There were several rounds of measurements, with testing starting in late 2023 and ending in the first half of 2024.
In November 2024, the SSL Annex published the Nucleus Lab Comparison (NLC) report, Part 1 – covering the four lamp artefacts in IC 2023. This report presents a comparison and demonstration of measurement equivalency of the five reference laboratories that constitute the core of IC2023. The five Nucleus Labs are based in Denmark, Korea, China (two labs) and the United States. The publication of this report is the first step in a formalised sequence of reporting from this interlaboratory comparison. With the reference values established and published, the individual test reports on the four lamp artefacts for each of the participating laboratories can be issued.
Publications Associated with IC 2023
IC 2023 Technical Protocol – this document describes the technical protocol used by the participating laboratories and the Nucleus Laboratories. It includes a description of the comparison artefacts, the assigned values, the measurement procedure and reporting requirements.
IC 2023 Nucleus Lab Comparison Report Part-1 – this report presents a comparison and demonstration of measurement equivalency of the five reference laboratories for the four lamp artefacts.
IEA 4E SSLC Platform Comment – AC Power Supply Issue – these comments were prepared and submitted to Members of three Expert Working Groups investigating temporal light modulation: CIE TC 2-89, IEC TC34 WG5 and IES LM-90 WG. These comments were intended to enable experts working on these committees to consider these preliminary findings on our on-going research into TLM measurements and certain AC power supplies used in test laboratories around the world.
