Most standard windows significantly reduce the amount of ultraviolet B (UVB) radiation that passes through them. UVB radiation is a component of sunlight primarily responsible for sunburn. This article explores the mechanisms of this blockage, influencing factors, and distinctions between ultraviolet radiation types.
Understanding UVB Radiation
Ultraviolet B (UVB) radiation is a segment of the electromagnetic spectrum with wavelengths ranging from 280 to 315 nanometers. This form of radiation carries higher energy than ultraviolet A (UVA) and primarily affects the outermost layers of human skin. Exposure to UVB is the direct cause of sunburn. Overexposure to UVB can lead to DNA damage within skin cells, contributing to the risk of skin cancers. Despite its harmful effects, UVB also plays a role in vitamin D synthesis in the skin.
How Standard Windows Interact with UVB
Common window glass, primarily composed of soda-lime glass, inherently blocks a significant portion of UVB radiation. The chemical composition of this glass naturally absorbs most UVB wavelengths, preventing them from penetrating indoors. A single pane of standard clear window glass can block nearly 100% of UVB rays. This absorption means typical residential and commercial windows offer substantial protection against the sunburning effects of UVB.
Double-pane windows, which consist of two layers of glass separated by a space, also effectively block UVB. While the primary benefit of double-paned windows is improved insulation, their glass components collectively ensure that very little UVB radiation passes through. This inherent filtering capacity is why it is rare to experience sunburn while sitting behind a closed window.
Factors Influencing UVB Blockage
Beyond standard clear glass, various window types and treatments can further enhance or alter UV blockage. Laminated glass, for instance, incorporates a thin plastic interlayer, typically polyvinyl butyral (PVB), sandwiched between two panes of glass. This interlayer is highly effective at absorbing ultraviolet radiation, blocking up to 99% of UV rays, including both UVA and UVB. This makes laminated glass an effective barrier against sun damage.
Low-emissivity (low-e) coatings are microscopic layers applied to glass surfaces to improve energy efficiency. Many of these coatings also offer substantial UV protection, often blocking between 75% and 99% of UV radiation. Tinted glass can reduce the amount of UV light transmitted, with effectiveness varying depending on the specific tint and composition. Aftermarket window films can block up to 99% of both UVA and UVB light, providing a cost-effective way to upgrade UV protection.
Distinguishing UVB from UVA
While standard windows are highly effective at blocking UVB, their performance differs significantly when it comes to UVA radiation. UVA rays have longer wavelengths, ranging from 315 to 400 nanometers, allowing them to penetrate deeper into the skin than UVB. While UVB primarily causes sunburn, UVA is associated with skin aging, such as wrinkles and age spots, and also contributes to the risk of skin cancer.
Standard clear window glass blocks only a limited amount of UVA, allowing between 25% and 75% of UVA rays to pass through. This means that even indoors, prolonged exposure near a window can still lead to skin damage from UVA radiation, unlike the effective blockage seen with UVB. Therefore, while you may not get sunburned through a typical window, the deeper penetrating UVA rays can still affect your skin.