Ultraviolet (UV) radiation is a form of electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays. It is divided into three main types based on wavelength and energy:
1. UV-A (Long-wave UV)
- Wavelength: 315–400 nanometers
- Penetration: Deepest into the skin (reaches the dermis)
- Proportion in sunlight: About 95% of UV radiation reaching Earth
- Effects:
- Causes skin aging (wrinkles, leathery texture)
- Contributes to skin cancer
- Can pass through glass and clouds
- Usage: Tanning beds, black lights, UV nail lamps
2. UV-B (Medium-wave UV)
- Wavelength: 280–315 nanometers
- Penetration: Affects the epidermis (top skin layer)
- Proportion in sunlight: About 5% of UV that reaches Earth
- Effects:
- Causes sunburn
- Strongly linked to DNA damage and skin cancer (especially melanoma)
- Triggers vitamin D synthesis in the skin
- Mostly blocked by the ozone layer, but some reaches the surface
3. UV-C (Short-wave UV)
- Wavelength: 100–280 nanometers
- Penetration: Does not reach Earth’s surface
- Proportion in sunlight: Fully absorbed by the ozone layer and atmosphere
- Effects:
- Extremely dangerous to all forms of life
- Can kill microorganisms by damaging their DNA
- Usage: Germicidal lamps for sterilization and disinfection