The fact that light was the first thing created during creation week is evidence of its environmental importance. Its benefits are so clear that one can understand why so many throughout history have worshipped the sun. The remaining one percent is made up of cosmic rays, gamma rays, x-rays, radio waves, and electric waves. Sunlight helps purify the environment by killing germs. UV is also responsible for the production of vitamin D in the skin.
Vitamin D is needed in calcium metabolism and bone production.
As skin grows thinner in old age, the amount of vitamin D produced is less. Sunshine has been shown to make neutrophils more efficient at ingesting germs and to increase the number of lymphocyes in circulation, thus strengthening the immune system. It tends to normalize blood pressure and decrease blood cholesteral. In diabetics, sunlight lowers blood sugar, apparently by stimulating the beta cells of the pancreas to more efficient production of insulin and by stimulating production of an enzyme, glycogen synthetase, which helps the liver remove glucose from the blood and store it as glycogen. Psychologically, sunshine is a mood elevator, probably by stimulating production of endorphins, producing for most people an increased sense of well-being and neuromuscular relaxation.