Insomnia is a symptom that there's an inability to fall asleep or to stay asleep as long as needed. The sleeping duration needed can be different to each person: some may need only 5 hours to wake up energetic, some may sleep 9 hours but still tired; however, the average is about 6-8 hours. Why is sleep important? Sleep in extremely important to human health, it enables the body to recover it self, enables the brain to process the information it received during the day, increases immunity, enables the endocrine system to adjust itself, and ensures the biological clock to be in the right cycle. It is also an important part of anti-aging and anti-cancer. Lack of sleep can cause slow reaction, headache, low immune ability, lack of concentration, memory problems, depression, irritability and an increased risk of heart disease. It is also bad for skin condition, cause wrinkles and melanin precipitation and accelerated aging. Why do we need to sleep early, and why do we need to turn off the light? Human body is more sensitive to the environment then we thought it is. Although we can't tell the exact direction by the sunlight like a migrating bird, and we can't detect the earthquake like the ants, but the sun light, the magnetic field, the temperature, the humidity and other factors of the environment does influence our body. As an example, Melatonin is one of the most important hormone that controls the quality of our sleep, our body release more Melatonin when it receive less light stimulation. It is the synchronizer of the biological clock, it is a antioxidant, and it can even prevent the damage to DNA. This shows how important it is to sleep in dark, and sleep early so the body can have enough time to sleep before the sun rise.