Inside every living organism resides a system of clocks that keep the body functions synchronized to the hours of the day and night. The master clock is the 24 hour clock. Then there is the 12 hour clock. There are other clocks that keep track of the seasons and years. What is important to note the clocks are affected by light and darkness. This triggers the body to behave in a certain ways. The second important fact is eating and weight; sleep and wakefulness; and work efficiency follows from light and darkness effects too. The third important fact is knowing the first 2 facts allow us to deal with sleep problems including jet lag; eating and weight gain, and work performances in a scientific way and hopefully result is a better You and Me.