Almost every living thing on this earth has functions dependent on living in an environment with a pattern of light and darkness. Dusk causes the beginning of a chemical process that each living things health and existence is dependent upon, including humans.
Medical studies indicate that exposure to artificial light at night negatively affects our health by tampering with our endocrine system. That process that begins at dusk would normally create a spike in the amount of melatonin in our bodies between midnight and 4 AM. Even very small amounts of light can suppress the production of melatonin enough to affect our sleep patterns and the rebuilding of our immune systems. People who work during the hours from midnight to 4 AM have a much higher incidence of breast and colorectal cancers. Melatonin has been proved to stop the growth of a common type of breast cancer cell during the hours of natural darkness when it peaks.