Andrew Huberman, Ph.D., a neuroscientist and professor at Stanford School of Medicine, highlights the importance of morning sunlight exposure for overall health. This simple, free practice is considered the most effective action for regulating the body’s sleep-wake cycle, or circadian rhythm. Viewers of his work, the Huberman Lab podcast, often seek his specific protocol for how much light is needed. Following these guidelines ensures the body’s internal clock is properly set, optimizing energy, mood, and sleep quality throughout the day.
The Biological Purpose of Morning Light
Bright light exposure shortly after waking serves as a powerful signal to the brain, initiating the body’s biological day. This light is detected by specialized cells in the retina called intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells contain the photopigment melanopsin and are separate from those responsible for vision. The signal travels directly to the suprachiasmatic nucleus (SCN), a small region in the hypothalamus that functions as the body’s master biological clock.
Activation of the SCN by morning light halts the production of the sleep-promoting hormone melatonin, which was elevated during the night. This light exposure also triggers a healthy, timed release of the hormone cortisol. Cortisol, often mislabeled as only a stress hormone, is necessary in the morning to promote wakefulness, enhance focus, and support the immune system. By setting the SCN, morning light effectively starts a timer that determines when the body will naturally begin to feel sleepy again, typically 14 to 16 hours later.
The Critical Timing Window
The timing of the light exposure relative to waking is the most important factor in this protocol. Huberman recommends getting outside to view the light within the first 30 to 60 minutes of waking up. Earlier exposure is always considered better, as it provides the strongest signal to the SCN. Delaying light exposure beyond an hour can lead to sleep phase delay.
This delay essentially pushes the entire circadian cycle later, making it harder to fall asleep at a reasonable time that evening. The light wavelengths present when the sun is low in the sky, known as low solar angle sunlight, are the most effective stimulus for the melanopsin cells. Receiving this signal early ensures the body’s clock is synchronized for the day ahead, reinforcing the natural cortisol spike.
Duration Guidelines Based on Weather
The duration of exposure is not fixed and must be adjusted based on the intensity of the light, which changes with the weather. This variability exists because the eyes need to register a sufficient level of light intensity (measured in lux) to effectively trigger the SCN. On a bright, sunny day, a short duration is usually enough. Huberman’s protocol suggests aiming for 5 to 10 minutes when the sky is clear.
When the day is cloudy or overcast, the light intensity is significantly lower, requiring a longer viewing time to achieve the same biological effect. On a cloudy day, the recommended duration increases to about 10 to 20 minutes. For heavily overcast or rainy days, the exposure time should be extended further, often requiring 20 to 30 minutes or more.
Even on the darkest days, outdoor light intensity remains substantially higher than typical indoor artificial lighting, making going outside necessary. If it is still dark when you wake up, use bright indoor lighting until the sun rises. Once the sun is up, you should move outside as quickly as possible, even if the sky remains heavily obscured.
Practical Application: Avoiding Common Mistakes
To ensure the light signal is strong enough, the exposure must take place outdoors. A common mistake is attempting to view the light through a window or windshield. Glass filters out many of the blue wavelengths of light that are most effective at activating the ipRGCs and setting the circadian clock. Viewing the light through a closed window can make the light 50 times less effective than viewing it directly outside.
Huberman advises against wearing sunglasses during this morning practice. Sunglasses block necessary wavelengths and reduce light intensity to a level too low to adequately stimulate the SCN. However, regular prescription eyeglasses or contact lenses are generally acceptable, even if they have UV protection. Remember that you should never look directly at the sun, as this can cause retinal damage. Instead, look toward the horizon or the general direction of the sun, shifting your gaze as needed to remain comfortable.