Sunlight brightens your mood. Just about everyone, regardless of whether or not they suffer from depression, feels better when the sun comes out. What most people experience intuitively has come to be understood scientifically in the past two decades: exposure to sunlight boosts serotonin levels in the brain. Sunlight (or bright light, to be more exact) is the most abundant and easiest to absorb anti-depressant you will find.
To receive your daily dose of bright light all you need to do is open your eyes. When bright light reaches the retina it stimulates the optic nerve, which sends a signal to the part of the brain that regulates production of serotonin and melatonin. Serotonin is the same neurotransmitter that is boosted by Prozac, Paxil, and the other selective serotonin re-uptake inhibitors. It relieves stressful feelings and produces a general sense of well-being. For depression, bright light works faster than medication, usually within a week, and with fewer side effects.
For more info, please read my articles on light at Rodale.com: