How does light affect melatonin?
Updated 2026-07-04
Melatonin is the hormone that signals 'night' to your body, and light is the main thing that controls its timing. In the evening, bright light, especially blue-cyan light around 480nm, can delay and reduce the natural rise of melatonin, pushing your sleepiness later. Dim, warm, blue-free light lets melatonin rise closer to its normal time. This is why the same light that is helpful in the morning works against you at night.
What melatonin does
As evening comes and light fades, your brain's master clock triggers the release of melatonin, which helps prepare your body for sleep. Its natural onset is one of the clearest markers of your internal night.
Melatonin does not knock you out like a sedative; it is a timing signal that says 'night is here'.
How evening light interferes
Light in the evening, particularly the blue-cyan part, tells your clock it is still daytime, which can hold melatonin back. Brighter and bluer light, closer to bedtime, has a larger effect.
Reducing that light, by dimming, warming and removing the blue, is the practical way to let melatonin rise on its normal schedule without taking anything.
Light versus melatonin supplements
Some people use melatonin supplements, especially for jet lag; that is a decision to discuss with a clinician, and dose and timing matter a lot. Managing your light is a complementary, drug-free way to work with your own melatonin rhythm, and it is something you control every evening.
Frequently asked
Does blue light suppress melatonin?
Yes. Blue-cyan light in the evening is the most effective wavelength range for suppressing and delaying melatonin, because it is what the body clock's light sensors respond to most strongly. The same light in the morning is beneficial.
How long before bed should I dim the lights to protect melatonin?
The last two to three hours before bed are when dim, warm, blue-free light helps most, so your evening light stops holding melatonin back.
Does warm light affect melatonin less than blue light?
Generally yes, because warmer light usually contains less of the blue-cyan signal. But warmth is only a proxy; two equally warm-looking lights can carry different amounts of blue, so what matters is the actual blue content, not just the color.
OIO is designed around this exact fact. In the evening it removes almost all of the blue signal from your light while keeping a warm white you can live by, so your room light is no longer the thing holding your own melatonin rhythm back. It makes no medical claims; it simply controls the light in the band that matters.
- CIE S 026:2018. System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light.
- Brown et al. (2022). Recommendations for daytime, evening and nighttime indoor light exposure. PLOS Biology.
- Berson, Dunn & Takao (2002). Phototransduction by retinal ganglion cells that set the circadian clock. Science.
- WELL Building Standard v2, Feature L03: Circadian Lighting Design.
This guide is general information about light and circadian rhythm, not medical advice. OIO is not a medical device and does not diagnose, treat or cure any condition. If you have a persistent or serious sleep problem, talk to a clinician.