The amount of ultraviolet (UV) radiation that passes through a window is important for both health and property preservation. The common belief that standard window glass provides total protection is a misconception. The actual amount of UV blocked depends entirely on the specific type of UV light and the composition of the glass or applied treatments.
The Difference Between UVA and UVB
Ultraviolet light is categorized into three types based on wavelength, which determines its energy and ability to penetrate materials and skin. UVC radiation (100–280 nanometers) is completely filtered by the Earth’s atmosphere and ozone layer, making it irrelevant for window consideration. The remaining two types, UVB and UVA, are the components of solar UV radiation that interact with glass. UVB rays (280–315 nanometers) are shorter and are the primary cause of sunburn, damaging the outermost layers of the skin. UVA rays (315–400 nanometers) are longer, penetrate deeper, and are strongly associated with premature aging and long-term skin cancer risk.
How Standard Clear Glass Performs
Standard window glass, known chemically as soda-lime silicate glass, offers a highly effective barrier against the shorter UVB wavelengths. This composition naturally absorbs nearly all UV radiation below 300 nanometers, typically blocking 97% to 100% of sunburning UVB rays. This is why a person rarely gets a sunburn while sitting next to a closed standard window. However, clear glass is significantly less effective at blocking the longer-wavelength UVA radiation, allowing 50% to 75% or more of ambient UVA to pass through the partially transparent UVA spectrum. Double-pane insulated glass units (IGUs) primarily improve thermal performance, and UVA transmission remains a concern unless specialized coatings are added.
Enhanced Protection from Specialized Windows
For true UV protection, specialized glass types or treatments are required to change the transmission profile across the UV spectrum. Laminated glass, created by bonding two panes with a Polyvinyl Butyral (PVB) interlayer, is exceptionally effective. The PVB interlayer is an efficient UV absorber, blocking up to 99% to 99.9% of both UVA and UVB radiation. This construction is mandatory for most vehicle windshields, providing superior protection compared to tempered side windows.
Low-emissivity (Low-E) coatings consist of thin metallic oxide layers primarily designed to reflect infrared heat for energy efficiency. These coatings also significantly improve UV blockage compared to plain glass, typically reducing harmful UV rays by 70% to 90%. More advanced, multi-layer Low-E systems can achieve even higher UV reduction, sometimes up to 95%.
Applied window films offer another highly effective solution, often achieving the maximum level of UV rejection. High-quality clear or tinted polyester films are engineered to absorb or reflect UV light, blocking between 99% and 99.9% of the total UV spectrum. These films can be installed on existing standard windows to upgrade performance to near-total UV protection without sacrificing visible light transmission.
Practical Implications for Health and Fading
The differential blocking performance of standard glass has important health implications, particularly during prolonged exposure through residential or vehicle windows. Since standard glass blocks the UVB rays that cause immediate sunburn, people often feel protected but remain exposed to the majority of UVA radiation. This chronic exposure contributes to photoaging, skin damage, and an increased long-term risk of skin cancer.
For property and furnishings, UV light is a major contributor to fading, though visible light and heat also play a role. The UVA radiation that passes through standard windows is a significant factor in the fading of furniture, artwork, and flooring materials. Upgrading to specialized solutions like laminated glass, Low-E coatings, or high-performance window films can substantially mitigate this damage by eliminating the UV component that accelerates material breakdown.