“Watching the sunset supports the human circadian rhythm by promoting sleepiness.”

Every subject had a later DLMO after the week of maximum versus minimum light exposure (average 1:03 h later, p<0.001). These results demonstrate that the light intensity people can generate at home in the few hours before habitual bedtime can alter circadian timing. People should reduce their evening light exposure to lessen circadian misalignment.

Evening light suppresses the pineal hormone melatonin, the biochemical signal of darkness. Ordinary room light (i.e., 100 lux or less) can induce these effects. The mean melatonin profiles showed significant increase in melatonin levels with time under dim light conditions, highest under dim light followed by C-LED and then FL.

For persons on a regular schedule (sleeping at night), bright evening light causes a phase delay (getting sleepy later and waking up later). In general, researchers estimate that light in the evening (about 2 hours before and after usual bedtime) can shift the circadian system about 2 hours later per day.

Light not only enables us to see fine detail, colour and motion, but also exerts non-visual effects on circadian rhythms, sleep and mood. Light at the wrong time may disrupt circadian rhythms and sleep, but in the form of light therapy, light exposure can be used as an intervention for psychiatric and other medical conditions. Roughly speaking, the effect of morning light is that it advances the clock, while evening and night light delays the clock.

The light/dark cycle of the sun has a powerful effect on the circadian clock, sleep, and alertness. Your body's circadian clock responds to light, as a signal to be awake, and dark, as a signal to fall asleep. Avoiding bright light 2 hours before bedtime will make it easier to fall asleep.

Spending time in bright light slows production of melatonin, which is the hormone whose nighttime spike helps make us sleepy. Lab tests showed that after only a week of camping free of artificial light and living by natural daylight, campers' daily melatonin rhythms and sleep schedules synced to the daily ebb and flow of light.

When exposed to only natural light, a person's circadian rhythm becomes closely synchronized with sunrise and sunset, staying awake during the day and sleeping when it's dark. In modern society, though, electricity creates an abundance of light sources that affect the brain's circadian pacemaker. Excess or poorly timed artificial light exposure can cause a person's circadian rhythm to be misaligned with the day-night schedule.

Researchers said the wavelengths at sunrise and sunset have the biggest impact to brain centers that regulate our circadian clock and our mood and alertness. The cone photoreceptor inputs to the circadian circuity respond to short wavelength blue light, but they also respond strongly to long wavelength oranges and yellows and contrasting light – the colors at sunrise and sunset.

Exposure to sunlight during the day helps your body produce melatonin, making it easier to fall asleep at night. As the sun sets, melatonin levels rise, signaling to your body that it’s time to wind down.

Researchers said the wavelengths at sunrise and sunset have the biggest impact to brain centers that regulate our circadian clock and our mood and alertness. The cone photoreceptor inputs to the circadian circuity respond to short wavelength blue light, but they also respond strongly to long wavelength oranges and yellows and contrasting light – the colors at sunrise and sunset.

“The sunset activates the signal to the brain that it will soon be time for sleep by increasing melatonin levels,” she says. Melatonin is the famed sleep hormone, and its night time release is crucial to facilitate a smooth transition from wakefulness to sleepiness. “Increasing exposure to light waves at sunset resets the circadian rhythm, precipitating deeper and more restful sleep overnight.”

Sunlight exposure after 3 p.m. also reduced the midpoint of sleep but to a lesser extent (-0:19 hh: mm; 95%CI: -0:36, -0:03; beta: -0.325; 95%CI: -0.600, -0.051). Furthermore, an increase in morning sun exposure was significantly associated with a lower PSQI total score, improving sleep quality (beta: -0.184; 95%CI: -0.362, -0.006).

Light exposure is one of the most powerful tools to shape your circadian rhythm, but the timing of light exposure can determine if it is beneficial or harmful. The circadian system modulates numerous bodily functions, including energy levels, body temperature and the secretion of hormones like cortisol and melatonin.

In the morning, sunlight helps to tell your circadian clock what time it is. In the afternoon, sunlight helps to make the clock stronger. At any time of day, getting sunlight means that the artificial light to which you are exposed at night will have less of an impact.

Red light therapy may support sleep quality and improve sleep inertia (grogginess upon waking), though more research is needed. Red light doesn't suppress melatonin production very much and may have positive effects on sleep, Dr. Rudraraju says. That said, red light can still negatively impact sleep when used at a high intensity, says Dr. Prabhakar.

By reintroducing wavelengths that mimic sunrise and sunset, you can anchor your daily rhythm, supporting energy, focus, and recovery in a way that feels effortless. Evening red light rituals help you re-establish the natural pattern: Promotes calm: Red wavelengths are non-stimulating, helping you unwind and prepare for rest. Supports restorative sleep: By encouraging melatonin release and reducing overstimulation, red light prepares your body for deeper, more restorative rest.

The secretion of the sleep signaling hormone melatonin by the pineal gland occurs only in darkness and is suppressed by blue light, thus altering the circadian rhythm. A Harvard study found that blue light suppressed melatonin for about twice as long as green light and shifted circadian rhythms.

Using amber, red, and near infrared wavelengths around sunset helps reinforce the shift toward darkness and supports the internal cues that prepare the body for rest. Red, amber, and near-infrared wavelengths allow melatonin to rise more naturally compared to blue-rich light, with evening studies showing melatonin levels more than three times higher under red light than under blue light.

Evening light exposure, including sunset wavelengths, triggers a circadian phase delay through melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). This phase delay shifts the circadian clock later, which delays sleep onset rather than promoting earlier sleepiness. The effect is opposite to what occurs with morning light exposure, which advances the clock and promotes earlier sleep.

Red light wavelengths (typically around 660 nm) are generally less disruptive to melatonin production than blue or white light, making them a candidate for evening use when you need some illumination without strongly suppressing sleep signals. Evidence for red light and sleep is promising but still limited, so claims should stay cautious. Red light therapy functions more as an adjunct rather than the primary driver of circadian reset.