Optimising metameric spectra for integrative lighting to modulate the circadian system without affecting visual...

Area of Science:

• Lighting technology and human health
• Photobiology and circadian science
• Color science and engineering

Background:

• Smart lighting aims to improve human health and wellbeing by leveraging light's effects on circadian rhythms, sleep, and cognition.
• Balancing visual preferences (illuminance, chromaticity) with circadian needs is challenging.
• Metametric spectral tuning offers a solution by modulating circadian impact independently of visual properties.

Purpose of the Study:

• To investigate the metameric tuning range for melanopic equivalent daylight illuminance (EDI) and melanopic daylight efficacy ratio (melanopic DER).
• To explore the potential of multi-channel LED luminaires in optimizing light for health and visual quality.
• To identify chromaticity regions suitable for controlling melanopic efficacy via spectral tuning.

Main Methods:

• Utilized 6-, 8-, and 11-channel LED luminaires with a fixed photopic illuminance of 250 lx.
• Systematically investigated the metameric tuning range across 561 chromaticity coordinates (2700–7443 K ± Duv 0–0.048).
• Applied color fidelity index (Rf) criteria (Rf ≥ 85, Rf,h1 ≥ 85) based on TM-30-20 recommendations.
• Optimized approximately 490,000 multi-channel LED spectra.

Main Results:

• Melanopic tuning range increases with correlated color temperature (CCT) and luminaire channel count.
• Maximum melanopic DER tuning ranges achieved were 0.24 (6-channel), 0.29 (8-channel), and 0.30 (11-channel).
• Melanopic EDI could be varied from 212.5–227.5 lx up to 275–300 lx without altering photopic illuminance or chromaticity.
• Highest metameric melanopic Michelson contrast values ranged from 0.16 to 0.18, achieved at specific CCTs and Duv values.

Conclusions:

• Metameric spectral tuning in multi-channel LED systems provides significant flexibility in modulating circadian light impact.
• This capability allows for optimizing light for human health without compromising visual quality.
• Identified specific chromaticity regions in the CIExy color space are crucial for effective melanopic efficacy control.