LIGHTING | LIGHT POLLUTION The blue, white and red Light pollution is about way more than too much light, as Iain Macrae FSLL MCIBSE explains F or nearly 100 years we have installed exterior lighting to provide illumination on roads and in outdoor spaces, so that people can enjoy the night-time, travel from here to there, and feel safer. Over that time, we have had many discussions on the latest and best solutions. Initially, light was for safety as we drove new-fangled cars at speed along roads trying to avoid pedestrians and cyclists. Along the way, we have researched and invested in better technologies and methods of lighting. From mercury lamps to LEDs, there has always been a reason to upgrade the latest and greatest story being the energy we save. The real question might be, why, at the same time, did we not see the mess we were creating in the way of light pollution? Sure, we have benefited people and it is safer to travel. There is better night-time entertainment, though research suggests we might be healthier adjusting our sleep patterns to the natural length of the day as the seasons change (Thomas Kantermann, 2007; Wright, 2009; Kohsaka, 1992). The impression is of greater community safety, though, in my area, it is rare that people use the all-night street lighting to take a walk, and the only house to be burgled in recent years sits right next to a streetlight. This feeling of safety, by the way, has a diminishing return above five lux (Svechkina, Trop and Portnov, 2020). The outcomes of night-time lighting have not been truly understood until recently. The body of evidence has been growing for more than a decade and, along with it, the number of concerned and protesting voices (see panel, Light pollution facts). We have underestimated the amount of light pollution and remained blind to how bad it really is. The facts opposite estimate an increase in light pollution between 270% and 400%, yet the measurement is only 45%. The blue in our story is largely about our failure to measure light pollution effectively sensors within the measurement satellites we have been using do not measure blue light. This has increased because many white LED street lights have a spectrum that contains a strong spike in the blue wavelength. That not only increases localised skyglow, but also has a particular and direct impact on life for the planets inhabitants, whether human, animal, insect or plant. What about white light generally? Two 50 December 2022 www.cibsejournal.com CIBSE Dec 22 pp50-52 Light pollution Supp.indd 50 25/11/2022 16:52