Excessive exposure to artificial light can take a toll on your muscles. People who work on computers or hospital workers can spend long hours under these conditions. Researchers at the Leiden University Medical Center in the Netherlands tested rats by placing one group in continuous light. The control group was placed in 12 hours of light and 12 hours of darkness (normal conditions). The group in continuous artificial light lost muscle strength, showed signs of osteoporosis, gained weight and their immune system suffered. Returning the rats to a normal light schedule however, reversed the symptoms. More testing has to be done but it seems the mind as well as the body need a period of complete darkness to revitalize.