How dark is your bedroom really? Answer 6 questions to find out how much light pollution is affecting your melatonin and deep sleep — with ranked solutions.
Light is the most powerful zeitgeber (time-giver) for the human circadian clock — and it works in both directions. Morning light is essential for anchoring the circadian rhythm, but light during sleep is one of the most potent disruptors of melatonin and sleep architecture available. Even very dim light — far below what the eye perceives as "bright" — suppresses melatonin and fragments sleep.
Research by Charles Czeisler and colleagues established that melatonin suppression begins at approximately 3–10 lux in the sleeping environment. Ten lux is comparable to a very dim corridor or the glow from a sleep mode indicator. This threshold is far lower than most people expect — streetlights through thin curtains, a phone on standby, a cable box LED, or a nightlight can all exceed this level. The brain's light-sensing apparatus (via ipRGC photoreceptors) is exquisitely sensitive precisely because detecting dawn light for circadian entrainment is a survival-critical function.
Blackout curtains or blinds are the highest-impact single change for most people — external light (streetlights, car headlights, urban light pollution) is typically the dominant source. Blackout curtains reduce light transmission by 99%+ when properly fitted. An eye mask achieves similar light elimination at lower cost and is portable. Covering LED indicator lights (use black electrical tape or purpose-made LED covers) eliminates the persistent low-level glow from electronics. Using red-wavelength nightlights (if any light is needed for navigation) significantly reduces melatonin suppression compared to standard white or blue nightlights.