Not All UV Is Blocked by Your Windows
Many people assume that being indoors — behind glass — means they're protected from the sun's ultraviolet radiation. The reality is more nuanced, and for people who spend significant time near windows at home or in the office, it's worth understanding what glass actually does and doesn't filter.
Ultraviolet radiation is divided into three bands:
- UVC (100–280 nm): Completely absorbed by the atmosphere before reaching ground level. Not a concern.
- UVB (280–315 nm): Responsible for sunburn. Standard glass effectively blocks UVB.
- UVA (315–400 nm): Penetrates deeper into the skin and is associated with long-term skin aging and contributes to skin cancer risk. Standard glass blocks only a portion of UVA — typically around 25–50% depending on the glass type and thickness.
The bottom line: ordinary window glass is not a UV shield. It filters UVB but allows substantial UVA to pass through.
Real-World Consequences
Skin Health
UVA rays penetrate the deeper layers of the skin (the dermis), breaking down collagen and elastin over time. This accelerates visible skin aging — wrinkles, uneven skin tone, and loss of elasticity. It also contributes to cumulative UV dose that raises skin cancer risk over years and decades.
Dermatologists have documented a well-known phenomenon: people who drive frequently show asymmetric sun damage on their left arm (driver's side window arm) compared to their right. Office workers seated near large, untreated south-facing windows face similar risks.
Eye Health
UVA exposure through windows can contribute to the development of cataracts and age-related macular degeneration over time. While single exposures are unlikely to cause immediate harm, cumulative lifetime exposure matters — especially for older adults who spend many hours near windows.
Furniture and Flooring Damage
UV radiation — particularly UVA — causes photodegradation of materials. This fading and bleaching effect is familiar to anyone who has had a sofa, rug, or hardwood floor discolor unevenly near a sunny window. Artwork, photographs, and textiles are particularly vulnerable.
How Different Glass Types Compare
| Glass Type | UVB Blocked | UVA Blocked | Notes |
|---|---|---|---|
| Standard single-pane glass | ~95% | ~25% | Most older residential windows |
| Standard double-pane glass | ~97% | ~35–45% | Better, but still lets significant UVA through |
| Low-E glass | ~99% | ~75–95% | Depends on coating type; some are UV-optimized |
| Laminated glass | ~99%+ | ~99%+ | PVB interlayer absorbs nearly all UV |
| UV-blocking window film | ~99%+ | ~99%+ | Retrofit option for existing windows |
Solutions for Reducing UV Transmission
UV-Blocking Window Film
The most accessible and cost-effective retrofit solution. High-quality solar window films — particularly ceramic and carbon types — block up to 99% of UV radiation across both UVA and UVB spectrums. They can be applied to existing windows without replacement and are available in a range of tint levels, including nearly clear options that don't affect the room's appearance significantly.
Laminated Glass
If you're replacing windows or building new, laminated glass (which includes a PVB or EVA interlayer) provides excellent UV protection as part of the window unit itself. This is also the safety glass used in car windshields and is standard in many modern commercial buildings.
Low-E Coatings
Low-emissivity (Low-E) glass has a metallic oxide coating that reflects infrared radiation and, depending on the specific product, also provides meaningfully improved UV blocking. Not all Low-E products are equal in UV performance — look for the UV transmission specification when comparing products.
Solar Shades
Even open-weave solar shades with a 1–5% openness factor block a significant portion of UV radiation — typically 85–95% depending on fabric and color — while maintaining the view and daylight. They're a non-permanent, renter-friendly option worth considering.
Practical Recommendations
- If you work near a window for several hours daily, prioritize UV-blocking window film or consider keeping a physical barrier like a solar shade deployed during peak sun hours.
- Valuable art, furniture, or flooring near windows benefits greatly from UV-blocking film — the investment can be far less than the cost of restoring or replacing faded items.
- When shopping for window film, verify the UV rejection specification, not just the solar heat rejection rating — these are different measurements.
Conclusion
UV radiation through windows is a real and manageable risk. Standard glass offers a false sense of security against UV exposure, but the solutions are straightforward, affordable, and readily available. Whether you choose window film, laminated glass, or a quality solar shade, taking action now protects both your health and your home's interior for years to come.