UV light (specifically, UV‑B) causes the body to produce vitamin D, which is essential for life. Humans need some UV radiation to maintain adequate vitamin D levels. According to the World Health Organization:
Vitamin D can also be obtained from food and supplementation. Excess sun exposure produces harmful effects, however.
Vitamin D promotes the creation of serotonin. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives. Serotonin is thought to provide sensations of happiness, well-being and serenity to human beings.