for human health. The major acute effects of UV irradiation on normal human skin comprise sunburn inflammation erythema, tanning, and local or systemic immunosuppression. The most deadly form, malignant melanoma, is mostly caused by indirect DNA damage from UVA radiation. This can be seen from the absence of a direct UV signature mutation in 92% of all melanoma. UVC is the highest-energy, most-dangerous type of ultraviolet radiation, and causes adverse effects that can variously be mutagenic or carcinogenic. Despite the importance of the sun to vitamin D synthesis, it is prudent to limit the exposure of skin to UV radiation from sunlight and from tanning beds. According to the National Toxicology Program Report on Carcinogens from the US Department of Health and Human Services, broad-spectrum UV radiation is a carcinogen whose DNA damage is thought to contribute to most of the estimated 1.5 million skin cancers and the 8,000 deaths due to metastatic melanoma that occur annually in the United States. The use of sunbeds is reported by the World Health Organization to be responsible for over 450,000 cases of non-melanoma skin cancer and over 10,000 cases of melanoma every year in the U.S., Europe, as well as Australia. Lifetime cumulative UV exposure to skin is also responsible for significant age-associated dryness, wrinkling, elastin and collagen damage, freckling, IGH, age spots and other cosmetic changes. The American Academy of Dermatology advises that photoprotective measures be taken, including the use of sunscreen, whenever one is exposed to the sun. Short-term over-exposure causes the pain and itching of sunburn, which in extreme cases can produce more-severe effects like blistering. Several countries (such as Australia) provide public forecasts of UV irradiation in the form of the UV Index. The index can be used as a guide to the public of dangers from over-exposure to sunlight, especially around noon, when direct sunlight is at its most intense. Benefits of optic exposure Light to the eyes, primarily blue-wavelength light, is important for the entrainment and maintenance of robust circadian rhythms. Exposure to sunlight in the morning is particularly effective; it leads to earlier melatonin onset in the evening and makes it easier to fall asleep. Bright morning light has been shown to be effective against insomnia, premenstrual syndrome and seasonal affective disorder (SAD). Effects on eyes Prolonged optical exposure to sunlight, especially intense ultraviolet light, may be linked to cortical cataracts, and high levels of