Bright light in the first hour after waking can strengthen the cortisol awakening response—a 30-45 minute hormone surge tied to alertness—and reduce the morning brain fog people often mask with caffeine.
Research cited in the report says retinal cells most sensitive to roughly 480-nanometre blue light signal the brain’s circadian clock, which then helps trigger cortisol release, raise core temperature and start the day’s alertness ramp-up.
Indoor lighting usually delivers only 100-500 lux, far below the 10,000-100,000 lux common outdoors on a clear morning, making offices and dim apartments poor substitutes for early natural light.
The report argues modern housing, curtains, underground commutes and window-poor workplaces quietly delay or flatten that morning calibration, pushing some people toward heavier stimulant use without addressing the underlying circadian mismatch.
A simple habit—stepping outside soon after waking—may help, though the report notes persistent fatigue has many causes and should be discussed with a doctor rather than blamed on light alone.