LIGHTING | LIGHT POLLUTION Photopic response Melatonin suppression Photosynthesis action spectrum 4,000K LED 1 0.8 Spectral efficiency Use of white light has also impacted insect populations. While you might like the fact there are fewer flies around to annoy you, the long-term ill effects on nocturnal species and plant pollination are already starting to show (Avalon C. S. Owens, 2020). That leaves us with a problem: how to reduce light pollution and, specifically, skyglow? The amount of skyglow increases near densely populated areas (Bierman, 2012) and our current light pollution guidance (ILP, 2020) allows for a further increase with every new installation. Guidance allows light onto faades in all but protected areas, and this light then reflects into the sky. Limits on upward light into the sky in rural, suburban and urban areas range from 2.5% to 15% for luminaires, meaning that new installations are allowed to add upward light, making the current situation even worse. If light pollution guidance sets targets that allow a site to increase upward light, then skyglow can only increase as our cities grow. Could it be time to ban upward light and limit faade lighting to buildings of historical importance? Light pollution guidance offers some solutions, including recommending fixtures that only emit light below the horizontal, and consideration of task focus and the amount of light. Even so, light often reflects off the faade, road, decking or paving, and this reflected light is still a concern. In the table, you might notice two LED solutions that offer an alternative way forward which brings us to the red in this article. Reducing the blue content of our light sources will definitively reduce skyglow. Using narrow band or phosphorcoated amber LEDs, while reducing colour rendering, will also impact skyglow. Red LEDs would go a step further. These light sources are not white light. For sure, your expensive electric vehicle paint work is going to look a little off colour parked on the street at night, but there is good evidence that using such technologies will significantly reduce the impact of human lighting on our ecosystem. Maybe its time to rethink our negative connotations of a red-light district and use this light for all our benefit. CJ 0.6 0.4 0.2 0 380 425 460 505 530 570 603 630 670 720 Wavelength (nm) Figure 3: Photosynthesis, human vision and melatonin response compared with typical LED spectrum. The blue peak of this LED directly overlaps human sleep and photosynthesis responses. Table 1: Skyglow brightness ratios for different light sources relative at 1km Lamp type Description Skyglow relative to low-pressure sodium NBA LED Narrow band amber LED 1.0 HPS High-pressure sodium 2.4 PC-A LED Phosphor-coated amber LED 2.4 2,400K LED Warm white LED 4.3 4,100K MH Neutral white metal halide 6.4 5,100K LED Cold white LED 7.9 Adapted from Luginbuhl, 2014. BLUES IN THE NIGHT Many white LED street lights have a spectrum that contains a strong spike in the blue wavelength, which is most effective at suppressing melatonin during the night. In the absence of electric lighting, humans begin the transition to night-time physiology at about dusk... These 4,000K lighting fixtures may contribute to delay in the transition, which could, at a minimum, reduce sleep quality. Of particular importance is the now voluminous data showing a higher risk of hormonally linked cancers with melatonin suppression, such as breast carcinoma (an increase risk of about 15%) and prostate carcinoma. The visual discomfort that can be created by very intense point sources, especially for older drivers, is magnified by higher colour-temperature LEDs because blue light scatters more in the human eye, leading to increased disability glare. Many beneficial insects are drawn to blue-rich lighting, and circle under them until they become exhausted and die... Even bridge lighting that is too blue has been shown to inhibit upstream migration of certain fish species, such as salmon returning to spawn. Extracts from LED street lighting: the human and environmental effects by Dr Mario Motta, Light Lines May/June 2022, special ROLAN issue IAIN MACRAE, CEng FSLL MCIBSE, is a past president of the Society of Light and Lighting (SLL), chair of SLL LG5: Lighting for Education, and member of British and European standards panels. He is founder of the training company Light Unwrapped. More information The May 2022 ROLAN (responsible outdoor lighting at night) Conference, co-organised by the SLL and Dr Karolina M Zielinska-Dabkowska, head of Illume, brought together world experts on artificial lighting at night. For selected articles by key speakers go to: bit.ly/CJNOV22LP1 52 December 2022 www.cibsejournal.com CIBSE Dec 22 pp50-52 Light pollution Supp.indd 52 25/11/2022 16:52