Correspondence: Obtrusive light, light pollution and sky glow: Areas for research, development and standardisation

Research on light pollution and artificial light at night (ALAN) has undergone rapid evolution, expanding from primarily astronomy into new disciplines. A keyword search in Scopus reveals a 466% increase from the number of papers published before 2011 (326) to those published between 2011 and 2020 (1846). Similarly, the number of papers in Lighting Research and Technology on these topics increased during the same period from 4 to 11. It is well known that ALAN can have adverse effects on surroundings in terms of sky glow, light trespass and discomfort glare, degradation of astronomical observations, health impacts and disturbance of ecosystems. Observatories need special curfews and light-protected areas to safeguard their ability to observe the stars. Nature reserves, stargazing locations and areas designated as protected habitats for rare and endangered species need to employ strict principles for design and use of light and lighting to prevent unwanted impacts. Hence, light pollution needs to be adequately addressed and counteracted by the lighting research community. In November 2020, a workshop on obtrusive light, arranged by Divisions 2 and 4 of the International Commission on Illumination (CIE) and the Technical University of Ostrava, convened researchers and professionals from different disciplines to discuss future research directions. In this correspondence we highlight six areas that were deemed important to improve the scientific and metrology basis and update international standards and guidelines to address global concerns with respect to light pollution. 1. Terminology. The CIE International Lighting Vocabulary defines light pollution as the ‘sum total of all adverse effects of artificial light’, whereas obtrusive light is defined as ‘spill light which, because of quantitative or directional attributes, gives rise to annoyance, discomfort, distraction, or a reduction in ability to see essential information such as transport signals’. However, it is unclear (i) whether artificial light must always be considered a pollutant, (ii) whether light pollution only takes place at night, (iii) what the difference is between light pollution and obtrusive light and (iv) whether the current effect-based definitions suffice to describe these terms. A commonly accepted and scientifically more precise terminology should be established to avoid confusion and serve various disciplines.