LIGHT EXPOSURE TIMER
When to get light, and when to avoid it
Light is the strongest signal your circadian clock reads. From your sleep schedule, this tool marks the morning window to seek bright light and the evening window to keep it warm and dim — the two moves that do most of the work.
MORNING BRIGHT LIGHT
07:00 – 07:30
Within minutes of waking, get 15–30 minutes of bright light — ideally outdoors. This anchors your clock to the day and sharpens daytime alertness.
EVENING DIM-DOWN
from 21:00
From about two hours before bed, switch to warm, dim light — under 50 lux at eye level. Bright or blue-rich light here pushes your clock later and blunts melatonin.
Your 24-hour light schedule
What actually counts
- Outdoor light wins. Even an overcast morning delivers 10,000+ lux — ten to twenty times more than a bright indoor room.
- Through glass is weaker. A window blocks much of the signal; step outside or open it when you can.
- Evening means warm and low. Aim for under 50 lux at eye level — lamps over overheads, warm bulbs, screens dimmed and shifted to night mode.
- Consistency beats intensity. The same light at the same time each day matters more than any single long session.
Why light timing moves your clock
Your circadian clock is set primarily by light. Light in the morning, after your core body temperature has bottomed out near the end of sleep, nudges the clock earlier — making it easier to fall asleep at night and wake on time. Light in the late evening does the opposite: it delays the clock and suppresses melatonin, the hormone that signals biological night.
The size of the effect depends on timing, not just brightness. The human response to light is steepest around the sleep period (Czeisler 1989) — which is why a short walk after waking and a dim two hours before bed do more than an extra hour of mid-afternoon sun. These windows are anchored to the schedule you enter; if your sleep times shift, the windows shift with them.
Sources
- Czeisler CA, Kronauer RE, Allan JS, et al. (1989). Bright light induction of strong (type 0) resetting of the human circadian pacemaker. Science, 244(4910), 1328–1333.
- Burgess HJ, Eastman CI (2005). The dim light melatonin onset following fixed and free sleep schedules. Journal of Sleep Research, 14(3), 229–237.
This tool is educational and not medical advice. Read our medical disclaimer.
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