How to measure light pollution-A systematic review of methods and applications

Artificial light at night (ALAN) is ever-present in modern society and has revolutionised our lives. Along with its many benefits, ALAN can have adverse effects that are studied across many fields, including astronomy, epidemiology, and ecology. This paper collates multi-disciplinary knowledge on measuring light pollution through a systematic review of 140 articles. The measurement tools used in each context are comprehensively discussed, gaps are identified in current techniques, and benchmarking information is provided to aid future research. It is found that no single device meets all measurement objectives, and opportunities exist for further development, such as refining low-cost imaging tools. The paper highlights that each tool's limitations must be acknowledged to avoid incorrect conclusions. Thorough experimental reporting, including details on instrument location and aiming, is also essential for the replication of research. Collaboration is needed to develop unified measurement techniques, units and terminologies rather than maintaining disciplinary silos. This will enable light measurement to keep pace with lighting technologies and the growing effects of light pollution.