Circadian metric variability measures for tunable LED light sources

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations


Circadian metrics quantify the non-image forming effects of light. Circadian metrics are based on the spectral power distribution (SPD) and intensity of a light source and human visual and non-image forming response to optical radiation. However, circadian metrics can only estimate static SPDs. Multi-primary LED systems generate a vast number of SPD combinations. A single metric cannot characterize the metric variation enabled by tunable solid-state lighting devices. There are no known metrics to quantify the capabilities of tunable lighting systems in terms of circadian metrics. A three-dimensional metric is proposed to quantify the variability in circadian metrics. The dimensions of the proposed circadian metric variability (CMV) are (a) a circadian metric, (b) energy efficiency metric, and (c) a lighting quality metric. Sample CMV measures are provided by generating SPDs in a seven-channel tunable lighting system at 20% dimming steps. Resulting in 279,936 test SPD combinations are filtered for nominal "whiteness"according to ANSI C78.377-2017 specifications. Each dimension of CMV is discretized by rounding the metric to significant figures. Each discretized unit of the CMV space can be considered significant or detectable different. The total volume of CMV represents the number of unique SPDs that can be created within a multi-primary LED system. A graphical representation of CMV shows the interrelation between different measures. CMV quantifies variation at the product level rather than in-situ variability of biological stimuli.

Original languageEnglish (US)
Title of host publicationLight-Emitting Devices, Materials, and Applications XXV
EditorsJong Kyu Kim, Michael R. Krames, Martin Strassburg
ISBN (Electronic)9781510642478
StatePublished - 2021
EventLight-Emitting Devices, Materials, and Applications XXV 2021 - Virtual, Online, United States
Duration: Mar 6 2021Mar 11 2021

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceLight-Emitting Devices, Materials, and Applications XXV 2021
Country/TerritoryUnited States
CityVirtual, Online

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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