Energy from the sun reaches the earth as visible, infrared, and ultraviolet (UV) rays.
1. Ultraviolet A (UVA) is made up of wavelengths 320 to 400 nm (nanometers) in length.
2. Ultraviolet B (UVB) wavelengths are 280 to 320 nm.
3. Ultraviolet C (UVC) wavelengths are 100 to 280 nm.
Only UVA and UVB ultraviolet rays reach the earth's surface. The earth's atmosphere absorbs UVC wavelengths.
→ UVB rays cause a much greater risk of skin cancer than UVA.
→ But UVA rays cause aging, wrinkling, and loss of elasticity.
→ UVA also increases the damaging effects of UVB, including skin cancer and cataracts.
The benefits of sunlight
1. Sunlight kills bacteria
2. Sunlight may reduce high blood pressure
3. Sunlight can regulate the immune system
4. Sunlight strengthens bones
5. Sunlight can improve sleep quality
