Light has a powerful impact on your body function and performance. When you get enough natural light, you sleep better at night, feel more alert during the day, and experience a boost in your mood.
How your internal clock works
Humans evolved to sleep at night, be active during the day, and use sunlight to adjust their internal clock to this schedule. In short, looking at the clock and seeing it’s 0700 hours doesn't help your body wake up for a new day. To wake up, you need to see sunlight—unless you have access to a lightbox that offers a brightness of 10,000 lux—so it goes into a brain region that acts as your internal clock. (Sunlight is much brighter than the artificial lights used in homes and offices, so it’s the most effective way to tell your brain it’s daytime.)
When the environment is dark or has low light, your brain produces the hormone melatonin. Its main function is to tell your brain it's dark outside and time to prepare your body for sleep. The light you see in the morning shuts down melatonin production and signals your internal clock it's time to wake up. Your brain then regulates all body functions accordingly to help you perform mentally and physically during the day.
In addition to controlling your wake-up and sleep times, your internal clock helps regulate changes in body temperature, hunger, alertness levels, and physical performance. Your eyes can also detect specific patterns of color and contrast at dawn and dusk, which help further align your internal clock with nature's light-dark cycle.
Here are some ways you can use light to optimize your performance.
Regulate your internal clock
You can use exposure to sunlight to fine-tune your internal clock with nature's light-dark cycle. These are examples of scenarios where you might benefit from adjusting your internal clock.
- Needing to wake up earlier. Whether you’re an early bird or a night owl is coded in your genes. Regardless of what time you’re naturally at your peak for energy, as a Service Member, you don’t always have a choice. If you’re naturally a night owl and need to wake up and be alert early, just one week of exposure to natural light as soon as you wake up—and avoiding screens before bed—can help.
- Adjusting to a new time zone. Exposure to sunlight as soon as you wake up can also make adapting to a new time zone faster and easier, especially when traveling eastward. You can benefit from this practice when you need to adjust to an earlier wake-up time too, such as when you “spring forward” at the beginning of daylight saving time.
- Recovering from shift work. After completing a few rounds of shift work, you might find it tough to go back to your old schedule. Daily exposure to sunlight at your previous regular wake-up time can help you adjust more quickly.
Increase alertness during the day
Starting your day with exposure to sunlight can boost your performance even if you don't need to realign your internal clock to nature's light-dark cycle. The more intense the light you see when you wake up, the sharper your melatonin levels drop, giving you more energy and alertness throughout the day to perform at your best.
It's common to feel tired between 1300 and 1500 hours. If you struggle with that early afternoon slump, take a short break and go outside for 5–15 minutes to help restore your alertness and mental performance for the rest of the day.
Sleep better at night
Regular exposure to sunlight early in the morning also improves your sleep. And the more light you get throughout the day, the better you sleep at night. When you’re exposed to sunlight in the morning, your brain starts to produce melatonin sooner, allowing you to fall asleep more easily at night. Seeing sunlight during the day makes it easier for your brain to detect nighttime too, even if you keep lights on after sunset. But if all you see throughout the day is artificial light, the much smaller difference in light intensity can't really help your brain recognize the beginning of nighttime. (Full daylight provides 10,000 lux of light intensity. A home lamp gives just 500 lux on average.)
Boost your mood
Exposure to bright natural light also increases the production of serotonin, a brain chemical that regulates mood in addition to supporting restful sleep. Having enough serotonin can help you feel happy and improve your sense of well-being.
If sunlight is available, it should be your preferred source of light to get all the benefits described above.
How to get enough safe sun exposure
- Get outdoors. The sunlight you get through windows is filtered and less intense than the light you get when you’re outside. When possible, go outside for maximum benefits.
- Don't look directly at the sun. Being outdoors is all you need to get the benefits of sunlight. Looking at the sun is dangerous and can damage your eyes.
- Shade is fine. You don't need to get sunlight directly on your face to get enough light to regulate your internal clock. You can stay in a shaded area and still get all the benefits.
- Do it first thing in the morning. Try to create the habit of getting sun exposure as soon as you wake up.
- Aim for at least 15 minutes. On sunny days, just 15 minutes of sunshine is enough to completely shut down melatonin production and wake up your brain. On overcast days, try to stay outside longer, but don't get discouraged if your schedule doesn't allow it. Natural light on an overcast day is still better than artificial light.
- Get sun exposure several times a day. The more light the better to align your internal clock and improve your sleep. When possible, try to get some light exposure around sunset too. Your eyes use light patterns at dusk to tell your brain night is coming, which can also help improve sleep.
- Do it safely. If you choose to be in direct sunlight, remember to wear protective clothing or sunscreen.
Sunlight is a major regulator of your internal clock and sleep patterns. If you struggle with poor sleep at night and lower energy and alertness during the day, you might benefit by making sure you get enough light in your daily routine. And remember: Light from screen-based devices is particularly bad for internal clock regulation and sleep quality. Using a smartphone or tablet before bed reduces sleep quantity and quality and increases daytime sleepiness.