Ultraviolet radiation

The ultraviolet band refers to a range of wavelengths ranging in width from about 100-380 nm (or 400, depending on which physics book you read). This band is, for important reasons, further subdivided into three more regions:

Solar UV Intensity Reaching Earth

UVC (100 to 280 nm): Thankfully, very nearly this entire band of very short wavelengths is filtered out by the earth's atmosphere, mainly by the ozone layer. This band of energy is lethal to life as we know it, causing severe disruption of biological processes. Artificially produced UVC is used to sterilize glassware and surgical instruments. (Sunburn with a vengeance.)

UVB (280 to 320 nm): Longer in wavelength than UVC, some UVB is blocked by the atmosphere, though a great deal reaches us, and excessive exposure causes sunburn and prolonged exposure to it over many years has been linked to skin cancer. Most UVB, however, is blocked by ordinary glass, which explains why it is much more difficult to get a sun tan through windowpanes.

UVA (320 to 380 nm): Longer still are the wavelengths of UVA. The longer the wavelength of radiation, the easier it is for it to pass through material objects. UVA readily passes through glass. Unfortunately, these waves are at just the right wavelengths to allow them to strongly and destructively interact  with organic molecules. From recent skin cancer studies, there is evidence that UVA may be more of a culprit than was previously suspected. It penetrates more deeply into the skin than UVB and may explain why the incidence of skin cancer has not been much affected by the use of sun screen lotions that only screen for UVB. According to the American Cancer Society, there are about 17,300 new cases of melanoma, and about 800,000 basal and squamous cell skin cancers, annually. There are about 2,100 melanoma skin cancer deaths per year ^{Reference 2}.   Many of us are aware that numerous (many often deadly) human diseases involve extreme sensitivity to UV light: lupus, xeroderma pigmentosum, and porphyria, for example. Fortunately, most high quality window film products can block the transmission of 99% or more of this band, as well as UVB, and so provide a substantial measure of shielding.

UV radiation is probably the single greatest factor contributing to the breakdown of organic materials (fabrics, plastics, dyes, wood, etc.) making up most of our home furnishings and automobile interiors. And the impact on our skin and eyes (in the development of cancer and the formation cataracts) is all too well known.