[Light therapy].

We all need light. Our bodies evolved for millions of years in a field of incoherent light from the sun, as did all our food sources. If you are feeling miserable in the depths of winter notice how uplifted you feel by the red holly berry, or the sparkling white when sunlight hits frosted trees. Plants use light for photosynthesis to manufacture carbohydrates. Animals and humans have receptors for light in the eye, and receptors in the skin. We are able to manufacture vitamin D from ultraviolet light, from the sun.