Light pollution / circadian disruption

Artificial light at night (ALAN) — from street lighting, screens and indoor illumination — suppresses melatonin secretion via intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing melanopsin, which are maximally sensitive to short-wavelength (~480 nm) blue light, thereby delaying or blunting the nocturnal melatonin surge and phase-shifting the master circadian clock in the suprachiasmatic nucleus. Chronic circadian misalignment is linked to impaired immune function, metabolic dysregulation, cardiovascular risk and accelerated epigenetic ageing. Epidemiological research by Erren and colleagues, along with multiple large cohort studies, has identified associations between ALAN exposure and elevated incidence of breast and prostate cancer, possibly through melatonin-mediated effects on cell proliferation. Urbanisation trajectories project continued increases in global ALAN intensity, making the biological effects of outdoor and indoor light environment increasingly relevant to public health.