Effective radiant flux for non-image forming effects—Is the illuminance and the melanopic irradiance at the eye really the right measure

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Summary

This paper argues that current integral metrics like illuminance and melanopic irradiance are insufficient to predict non-image forming (NIF) effects because ipRGCs are not uniformly distributed or equally sensitive across the retina. It introduces a spatially resolved effective radiant flux model, suggesting that luminance in the central visual field may be a more critical driver of NIF responses than overall illuminance, which could explain inconsistencies in the existing NIF research literature.

Key Findings

ipRGCs are not evenly distributed across the retina, meaning equal vertical illuminance does not guarantee equal NIF stimulation.
Typical office lighting solutions may have lower NIF effectiveness than lighting setups with higher luminance concentrated in the central field of view, even when overall illuminance values are matched.
The proposed spatially resolved model suggests that standard metrics (illuminance, melanopic irradiance) may be inadequate for accurately characterizing circadian or alerting light exposures in real environments.

Categories

The Science of Light: Proposes a spatially resolved model of ipRGC stimulation that challenges the use of simple illuminance or melanopic irradiance as sufficient measures for non-image forming effects.

Workplace Performance: Findings have direct implications for office lighting design, suggesting that luminance distribution in the visual field matters for NIF effectiveness, not just overall illuminance levels.