On lamps, walls, and eyes: the spectral radiance field and the evaluation of light pollution indoors

TL;DR

This paper investigates how indoor light spectra are affected by surface reflections and proposes a model to evaluate spectral modulation, aiding lighting design and understanding light pollution indoors and outdoors.

Contribution

It introduces a spectral radiance field model that accounts for surface reflections, providing a new framework for assessing indoor light spectra and pollution.

Findings

Spectral modulation by surfaces can significantly alter light exposure.

Effective filter-like functions describe spectral effects for factorizable sources.

The model links indoor and outdoor light pollution studies.

Abstract

Light plays a key role in the regulation of different physiological processes, through several visual and non-visual retinal phototransduction channels whose basic features are being unveiled by recent research. The growing body of evidence on the significance of these effects has sparked a renewed interest in the determination of the light field at the entrance pupil of the eye in indoor spaces. Since photic interactions are strongly wavelength-dependent, a significant effort is being devoted to assess the relative merits of the spectra of the different types of light sources available for use at home and in the workplace. The spectral content of the light reaching the observer eyes in indoor spaces, however, does not depend exclusively on the sources: it is partially modulated by the spectral reflectance of the walls and surrounding surfaces, through the multiple reflections of the light beams along all possible paths from the source to the observer. This modulation can modify significantly the non-visual photic inputs that would be produced by the lamps alone, and opens the way for controlling -to a certain extent- the subject's exposure to different regions of the optical spectrum. In this work we evaluate the expected magnitude of this effect and we show that, for factorizable sources, the spectral modulation can be conveniently described in terms of a set of effective filter-like functions that provide useful insights for lighting design and light pollution assessment. The radiance field also provides a suitable bridge between indoor and outdoor light pollution studies.