Skyglow inside your eyes: intraocular scattering and artificial brightness of the night sky

TL;DR

This study quantifies how intraocular scattering significantly contributes to perceived sky brightness, especially near streetlights, and suggests lighting design strategies to reduce intraocular skyglow and improve night sky visibility.

Contribution

It provides the first quantitative assessment of intraocular scattering's role in artificial skyglow and offers practical recommendations for urban lighting to mitigate this effect.

Findings

Intraocular scattering significantly increases perceived sky brightness near streetlights.

Blocking direct light from lamps can substantially improve star visibility.

Lighting at large angles reduces intraocular skyglow.

Abstract

The visual perception of the natural night sky in many places of the world is strongly disturbed by anthropogenic light. Part of this artificial light is scattered in the atmosphere and propagates towards the observer, adding to the natural brightness and producing a light polluted sky. However, atmospheric scattering is not the only mechanism contributing to increase the visual skyglow. The rich and diverse biological media forming the human eye also scatter light very efficiently and contribute, in some cases to a big extent, to the total sky brightness detected by the retinal photoreceptors. In this paper we quantify this effect and assess its relevance when the eye pupil is illuminated by light sources within the visual field. Our results show that intraocular scattering constitutes a significant part of the perceived sky brightness at short distances from streetlights. These results provide quantitative support to the everyday experience that substantial gains in naked-eye star limiting magnitudes can be achieved by blocking the direct light from the lamps that reaches the eye pupil. Urban lighting designs that reduce the illuminance over the eye pupil and locate the sources at large angles with respect to the visual axis are expected to help decreasing the artificial intraocular skyglow.