Artificial light at night (ALAN) is a pervasive environmental phenomenon, transforming natural nighttime landscapes globally. This human-made illumination, known as light pollution, has dramatically increased with urban expansion and lighting advancements. ALAN alters the natural rhythm of day and night, impacting both human health and ecological systems.
Understanding Artificial Light at Night
Artificial light at night includes misplaced or excessive illumination that disrupts natural darkness. Skyglow is a diffuse glow over populated areas, visible many miles from its source due to light scattering. Glare describes intense, unshielded light that can impair vision. Light trespass occurs when unwanted light spills onto adjacent properties or natural areas.
Common sources include unshielded streetlights, commercial buildings, sports venues, residential outdoor lighting, advertising billboards, and vehicle headlights. Modern lighting technologies like light-emitting diodes (LEDs), incandescent bulbs, and fluorescent lamps vary in their light spectrum. Many contemporary LED lights, for instance, emit more blue light, which affects biological systems.
Impact on Human Health
Exposure to artificial light at night can disrupt the human circadian rhythm, the body’s natural internal clock. The brain’s suprachiasmatic nucleus (SCN) is sensitive to light, especially blue-rich wavelengths from modern lighting and screens. Evening light exposure can suppress melatonin, a hormone that signals darkness and promotes sleep.
Melatonin suppression and circadian rhythm disruption can reduce sleep quality and duration. Chronic sleep disturbances are linked to an increased risk of health issues, including metabolic disorders like obesity and type 2 diabetes, and cardiovascular issues such as hypertension and heart disease. Altered light-dark cycles can also contribute to mood disorders like depression and anxiety. Maintaining natural light-dark cycles supports human well-being.
Ecological Consequences
Artificial light at night affects wildlife behavior, altering natural patterns. Migratory birds use celestial cues for navigation; bright city lights can disorient them, leading to collisions or altered paths. Newly hatched sea turtles are drawn to bright lights, diverting them from the ocean towards inland hazards.
Nocturnal animals, relying on darkness, experience habitat fragmentation and reduced activity due to artificial illumination. Insects are attracted to artificial lights, leading to exhaustion, increased predation risk, and altered population dynamics. This can reduce pollinator populations and disrupt nocturnal food chains. Plants also experience consequences, as ALAN can disrupt their photoperiodic responses, affecting flowering times, dormancy, and growth cycles. These disruptions impact ecosystem functions and biodiversity.
Solutions and Mitigation Strategies
Addressing light pollution involves responsible lighting practices. Using warm-colored lights (below 3000 Kelvin) reduces disruptive blue light. Shielding lights to direct illumination downwards prevents spill into the sky or unwanted areas, ensuring light is used only where needed.
Dimming or turning off lights when not in use conserves energy and reduces light pollution. “Dark sky friendly” lighting promotes fixtures that are fully shielded, use warm-colored bulbs, and are appropriately dimmed. Broader initiatives include establishing dark sky parks and reserves to protect naturally dark environments. Communities can adopt outdoor lighting ordinances. Individuals can contribute by using blackout curtains and reducing screen time before bed.