From Lux to Biology: A Critical Review of Artificial Light at Night and Circadian Health Implications

Artificial lighting is essential to modern society, enabling safety, productivity, and economic activity after dark. However, a growing body of research shows that light, especially artificial light at night (ALAN)—also acts as a biological signal that can disrupt the body’s internal clock (circadian system). This review critically examines how light exposure affects human health, drawing on key findings from chronobiology, neuroscience, and environmental health.
A structured landmark study approach was used to select twelve highly influential studies based on their scientific impact, methodological rigour, and role in shaping current understanding. These studies were grouped into four core domains: (1) discovery of the melanopsin-based non-visual photoreception system, (2) associations between ALAN, night work, and cancer risk, (3) dose–response relationships between light exposure and melatonin suppression, and (4) spectral sensitivity to short-wavelength (“blue”) light.
Across these domains, consistent evidence shows that biological responses to light are primarily influenced by three factors: the amount of light reaching the eye (corneal illuminance), the timing and duration of exposure, and the spectral composition of light, particularly blue-rich wavelengths. Importantly, commonly used lighting measures such as lux—designed for visual performance—do not adequately capture these biological effects.
This review identifies key gaps between scientific knowledge and real-world application, including inconsistent measurement of light exposure, limited long-term field studies, and insufficient integration of biologically relevant metrics into lighting standards. The main contribution of this work is to synthesise landmark evidence into a clear, interdisciplinary framework that bridges science, engineering, and policy. It highlights the need to move beyond conventional lighting metrics toward biologically informed design and regulation, such as incorporating spectral weighting, exposure timing considerations, and eye-level measurements into standards.
Policy and practical implications include revising outdoor and indoor lighting guidelines to minimise harmful nighttime exposure, informing public health recommendations, and guiding the design of LED systems that balance visibility with human well-being. This study is a focused, landmark-based critical review rather than a full systematic review, intended to clarify foundational evidence and accelerate its translation into practice amid the rapid global expansion of artificial lighting.

Artificial light at night; circadian disruption; melanopsin; melatonin suppression; spectral sensitivity

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