What is ultraviolet light?
Light has a wide bandwidth, from ultraviolet at the lower end to infrared at the upper end. Neither end is visible to the human eye. Near the middle is the visible light spectrum, what we see. Ultraviolet light is broken into different bandwidths: UVA (315 to 400 nanometers), also known as black light, is used for safe skin tanning and to treat certain skin disorders. UVB (290 to 315nm) is that part of sunlight that leads to sunburn and skin cancer. Most of solar UVB is absorbed by the stratospheric ozone layer. UVC (220-290nm) includes germicidal UV and can be used for air, surface and water disinfection. Overexposure causes skin redness and eye irritation, but does not cause skin cancer or cataracts. UVV (187nm) is naturally occurring (from lightening you get that fresh smell after a thunderstorm) but doesn’t usually penetrate the upper atmosphere.
Ultraviolet light has a shorter wavelength than visible light and therefore has more energy. UV can be divided into three groups according to wavelength, UV, UVB, and UVC. UVA has been shown to penetrate the lower layers of skin, and is associated with aging. UVB can cause keratitis, and is associated with cataracts. UVC is the shortest wavelength and is almost entirely blocked by the upper atmosphere. Sunglasses, which protect against these three types of UV light are essential equipment.
