Life Kit: Health How to optimize your circadian rhythm
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Dec 4, 2025 
NPR health correspondent Will Stone shares groundbreaking insights on the impact of light on our health. He discusses a study revealing that excessive evening brightness can increase mortality risks, while daytime light is beneficial. Stone emphasizes the importance of our internal clocks and offers practical advice: aim for 45 minutes of morning sunlight and keep evenings dark with blackout curtains. He also explains how modern lighting disrupts circadian rhythms, urging listeners to rethink their light habits for better health.
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Streetlight Sneaks Through Curtains
- Mariel Segarra describes battling streetlight glow that sneaks around blackout curtains into her bedroom.
- This personal struggle illustrates how common light intrusion at night is for many people.
Massive Light-Tracking Study
- Will Stone summarizes a large UK Biobank study that tracked ~90,000 people with wrist sensors recording light for eight years.
- The dataset produced about 13 million hours of light data to analyze links between light exposure and mortality.
Day–Night Light Contrast Affects Longevity
- The study found bright nights increased mortality risk by 21–34% and bright days reduced it by 17–34%.
- People with bright nights and dark days could live up to five years less than those with bright days and dark nights.