90% of the time, we live under artificial light, and our biological clock notices it
- Jorge Marten Groen
- Mar 10
- 3 min read
“Ninety percent of our time, we’re exposed to electric light. Our eyes can adapt, but our biological clock cannot.” Those were the words of chronobiologist Marijke Gordijn at the Sleep Disorders Congress organized by BSL Media & Learnin and they stuck with me. They sparked my curiosity to explore the topic more deeply.
Light is a powerful signal for the body. It influences our biological clock, sleep, mood, and cognitive performance. But it’s not just about how bright the light is. It also matters when and what type of light we’re exposed to.
Natural daylight can be 25 to 50 times stronger than artificial light and contains far more blue-spectrum light, which plays a key role in regulating our biological clock. By contrast, in most workplaces—or even the conference hall where I heard Gordijn speak—light levels are often hundreds of times lower than outside in daylight.
How strong is light?
Light intensity, measured in lux, can vary enormously—from the faint glow of the moon to the brilliance of midday sun. Color temperature also matters: daylight is rich in blue light, while warm indoor light in the evening has far less, which is better for sleep. Here’s a rough guide:
Situation | Approx. lux | Blue light impact |
Starry night (no moon) | 0.001 – 0.01 lux | Practically no effect |
Full moon | 0.1 – 1 lux | Can influence sleep if bright |
Weak nightlight | 1 – 10 lux | May slightly suppress melatonin if shining directly in eyes |
Living room lighting | 50 – 150 lux | Slight disruption possible, especially with cool/white LED lights |
Office lighting | 300 – 500 lux | Often noticeable effect on the biological clock during the day |
Outdoors on a cloudy day | 1,000 – 5,000 lux | Plenty of blue light, ideal for syncing the internal clock |
Direct sunlight | 50,000 – 100,000 lux | Maximum natural stimulation of the biological clock |
Synchronizing with the 24-hour cycle
Light helps the internal clock in our brain stay aligned with the 24-hour day-night rhythm of the Earth. Without a strong enough signal, the internal clock can drift, leading to sleep problems. The 24-hour sleep-wake disorder is common in blind individuals, but nowadays, sleep clinics are seeing more young people with disrupted biological clocks—often sitting in waiting rooms with sunglasses and hoodies, sensitive to light after nights spent in front of screens.
The good news is that light is a controllable factor you can use to improve your sleep. Getting more daylight during the day—through a morning walk or a quick stroll at lunch—strengthens the day-night signal. Many people notice they sleep more deeply and wake up less often.
Equally important is limiting light exposure in the evening. Low evening light levels and darkness at night help the body maintain a healthy light-dark rhythm. Interestingly, people who spend more time in daylight during the day often report sleeping better.
The website Light for Public Health offers a consensus by scientists on the role of light for health, including guidelines for daily light exposure.
☀️ Daytime/Morning
Aim for at least 250 lux at eye level. In practice, this means going outside regularly, working in a well-lit space, or sitting close to a window. Experts recommend seeking daylight shortly after waking up.
🌆 Evening
About three hours before bedtime, reduce light exposure to ≤10 lux at eye level. Use warm, dim lighting with minimal blue light.
🌙 Night
Ideally, your bedroom should be almost completely dark—less than 1 lux. A weak nightlight (1–10 lux) should not shine directly into your eyes or be placed too close to the bed. Dim lights in the bathroom and toilet at night.
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