2. Light Always Wakes Up Your Body

Our bodies are meant to wake up with the dawn. Before electric lights, our ancestors had to wake up with the dawn to get as much done as possible during the light of the day. The pattern of going to sleep at sunset and waking up at sunrise is woven into our basic biology. Our bodies are literally genetically programmed to wake up in response to sunlight. Critically, during most of evolutionary history, the sun was the only bright light source around. Moon and star light, and even the light from candles and fires, isn’t nearly as bright as sunlight even on a cloudy day. As a result, our genes developed a simple program: wake up the body in response to light.

In the modern world electric lights can play havoc with this program. Electric lights are a lot brighter than candle light or fire light. As a result, exposure to electric light has a stimulatory effect on the body similar to that of sunlight. When you were a kid, did your mom ever come in when you were still asleep at noon and flip on every light in your room? If so, it woke you up fast, right? And even when you turned the lights off, you probably couldn’t get back to sleep. Once our bodies are exposed to light, and the flow of wake up chemicals like cortisol gets going, it keeps going for several hours. What this means is that if you expose yourself to bright light late at night, it can really interfere with your ability to fall asleep and sleep deeply.

Try to avoid brightly lit rooms, TV screens, and especially computer screens (since when using a computer you're staring at an intense light source from close range), within 2 hours of your bed time. Many people who routinely have troubble falling alssep at night find it much if they stop using the computer after 8pm. In addition, make your sleep environment as dark as possible. Any amount of light stimulates the body. Researchers at Stanford showed that a pen light shined on the bask of someone’s knee can disturb their sleep. Even a bright LCD alarm clock or a street light shining in through your window can make it harder to fall asleep or reduce sleep quality.