The Spectral Optimization of a Commercializable Multi-Channel LED Panel With Circadian Impact

Abstract

There exists a need for the design of light emitting diode (LED) luminaires which can deliver both visual and non-visual benefits of light to humans. In this work, we introduce an optimization approach based on spectral shaping for a minimalistic and practical design of a circadian-tunable multi-channel luminaire which also outputs white light with high quality and luminous efficacy of radiation (LER). The spectral optimization approach utilizes Multi-objective Genetic Algorithm to maximize circadian tunability, light quality and LER while minimizing the number of channels. Solution sets are constrained using the non-visual quality metric, Melanopic Efficacy of Luminous Radiation (MELR) from the Melanopic Equivalent Daylight Illuminance (MEDI) approach and the more stringent visual quality metric TM-30 in addition to conventional Color Rendering Index (CRI). By matching theoretically optimized LED parameters to commercially available LED parameters for commercialization purposes, we establish the maximum MELR tunability that is achievable with 4 and 5 LED channels and the resulting trade-off in efficacy and light quality. Based on the results and analysis in this work, we detail a spectral optimization approach to propel the field of indoor lighting towards human-centric lighting.

Melanopic Limits of Metamer Spectral Optimisation in Multi-Channel Smart Lighting Systems

“…Thus, multi-channel luminaires have the advantage of varying visual metrics while maintaining circadian effectiveness. In this context, the work of Saw et al recently recommended that at least 4 to 5 LED channels are enough to achieve an optimal balance between colour fidelity and circadian tunability [61]. Our results also reveal such a tendency, which is why we can conclude that an 8-channel or 11-channel luminaire does not have a significant advantage for non-visual lighting purposes.…”

“…Compared to previous spectral optimisation studies [6,58,[60][61][62][63]100,101,[115][116][117][118], this work provides at the authors' best knowledge one of the most comprehensive multichannel LED datasets for metamer spectra. More advanced analyses between additional colour quality metrics are possible with the optimised spectra, which we did not fully exploit.…”

“…The implementation of the custom metamer optimisation approach will not be described here as it is part of an upcoming publication. However, metamer spectra can also be optimised using gradient-based or classical black-box heuristic optimisation approaches, as discussed in recent works [58,61,91,[98][99][100][101]. Through the optimisation, metamer spectra for 473.2 ±SD 18.83 of the 561 given chromaticity targets (Figure 2a, Figure S3) were found on average for each channel configuration and luminance levels (Table S2).…”

“…Modern indoor lighting faces the challenge of finding an appropriate balance between legal requirements, energy-saving, visual performance and non-visual impact [6,[58][59][60][61]. In this context, multi-channel LED luminaires are of interest because such systems can vary spectra over time to address different visual or non-visual processes precisely [7,62,63].…”

Fundamental Spectral Boundaries of Circadian Tunability

“…With a parametric model of just 3 parameters, constrained to CRI = 90, it was found that changing the CCT from 2700K to 6500K induced a maximal CAF range from 0.294 to 0.957 [27]. In terms of MELR, a recent study showed that under CRI, Duv and TM-30 constraints, a MELR tunablity from 0.43 to 1.82 mW/lm is possible for a 5-channel luminaire, when varying between CCT's of 2700K and 10000K [28].…”