Keeping the Nights Dark: How Nighttime Light Threatens Sleep and the Brain

By Ram Rao, Ph.D., Principal Research Scientist for Apollo Health

In today’s world of glowing screens, LED streetlights, and bedside gadgets, darkness has become increasingly rare. Yet, our physiology is designed for bright days and dark nights. Even a small amount of Artificial Light At Night (ALAN) can disrupt the body’s internal clock with far-reaching consequences for sleep quality, mood, cognitive performance, and overall brain health. Our body’s circadian rhythm relies on daily light and dark cycles. At night, darkness signals the brain to release melatonin, which promotes deep, restorative sleep.

Exposure to light, especially blue wavelengths that are common in screens and LED bulbs, suppresses melatonin, delays sleep onset, and reduces time spent in slow-wave and REM sleep. These sleep stages are crucial for building new memory circuits, consolidating memories, regulating emotions, and repairing the brain. Animal studies show that as little as one hour of light at night can disrupt brain functions, underscoring the potential risks of nighttime light exposure.

Recent studies highlight that light at night is not just a nuisance; it is a genuine health hazard. Results from these studies indicate the following:

• Neuroinflammation and cognitive decline: Disrupted sleep contributes to memory impairment and may increase long-term risk for Alzheimer’s disease.
• Mental health issues: Higher levels of night light exposure raise the risk of depression and anxiety, while bright daytime light lowers it.
• Metabolic and cardiovascular strain: Even dim ambient light can elevate blood sugar levels, impair insulin sensitivity, and increase heart disease risk.

Young brains are particularly vulnerable to night light. Studies show that irregular light cycles or even brief nighttime light exposure can disrupt children’s sleep, resulting in poor brain development. Thus, it appears that minimizing light at night and maximizing daylight exposure are simple, science-backed steps to protect sleep and long-term cognitive wellbeing. Here are some practical steps for healthier nights:

• Use red or amber nightlights instead of bright or blue light.
• Dim screens or use blue-light filters in the evening.
• Ensure bright daylight exposure in the morning and throughout the day.
• Keep bedrooms dark and cool with blackout curtains or eye masks.

Protecting the natural rhythm of light and darkness is a simple yet powerful tool for better sleep, sharper cognition, and long-term brain health. By embracing daylight and preserving nighttime darkness, we align with our physiology and give our brains the rest they need to thrive.