The Hidden Costs of Light: A Critical Review of Artificial Light at Night (ALAN) and Its Health Implications
Uthayan Thurairajah
*
WSP Canada, 150 Commerce Valley Dr W., Thornhill, Ontario, L3T 0A1, Canada.
*Author to whom correspondence should be addressed.
Abstract
The electrification of the modern world has fundamentally altered humanity's relationship with darkness. The invention of electric light has revolutionised daily life with dramatic changes to light conditions at night. Artificial light, once regarded as an unqualified technological triumph, is now increasingly scrutinised for its multifaceted biological and ecological consequences. Along with the growth of light at night, the negative effects of excessive outdoor Artificial Light at Night have been recognised by researchers and policymakers as “light pollution”. This narrative review critically synthesises pioneering and contemporary research on artificial light at night (ALAN) and its implications for human health, drawing upon evidence from molecular biology, epidemiology, clinical science, and environmental studies. Literature was identified through searches of the major academic database and the search encompassed publications from 2007 to 2026. The review examines how chronic exposure to artificial illumination—particularly short-wavelength blue light—disrupts the human circadian system by suppressing nocturnal melatonin secretion and desynchronising central and peripheral biological clocks. The oncological consequences of circadian disruption are evaluated, with particular attention to the epidemiological association between ALAN exposure and elevated risks of breast and other cancers. Metabolic derangements, including obesity, insulin resistance, dyslipidaemia, and cardiovascular disease, are examined as downstream consequences of circadian misalignment. The neuropsychological burden of artificial lighting is analysed through its effects on sleep architecture, mood regulation, and cognitive function. The accelerating proliferation of light-emitting diode technologies and digital screens introduces specific considerations relating to ocular health and the chronobiological effects of evening blue light exposure. Vulnerable populations—including night shift workers, children, and the elderly—are identified as bearing a disproportionate share of health risks. The global problem of light pollution and its broader ecological ramifications are addressed. Evidence-based mitigation strategies and significant research gaps are identified. The totality of evidence reviewed here supports a conceptual shift in how artificial lighting is understood within public health discourse.
Keywords: Artificial light at night, circadian disruption, melatonin suppression, light pollution, sleep disorders, cancer risk, metabolic syndrome