How Much UV Radiation Can Low-E Glass Attenuate？

Based on the measured data from Aoptek GlasSpec2500, the UV attenuation capacity ranks from strongest to weakest as follows: Low-E insulating glass > clear insulating glass > ultra-clear insulating glass. The specific performance is detailed below:

1. Low-E Insulating Glass: blocks over 65% of UV radiation, medium-wave ultraviolet (UVB) with a wavelength of less than 315nm is almost impenetrable. Compared with ultra-clear insulating glass and clear insulating glass, Low-E insulating glass can attenuate more UV radiation, thereby reducing the amount of UV rays incident on the interior to a certain extent.

2. Standard Insulating Glass (Clear): With an approximate UV attenuation rate of 50%, it also achieves nearly complete blocking of UVB. However, its overall attenuation performance is slightly inferior to that of Low-E insulating glass.

3. Ultra-Clear Insulating Glass: Its UV attenuation rate is only about 24%. The transmitted UV radiation is mainly long-wave ultraviolet (UVA), with a certain amount of UVB still penetrating—complete blocking of UVB cannot be achieved.

The UV blocking effect of Commen Insulating Glass

The GlassSpec2500 building glass spectrophotometer is used to measure the ultraviolet transmission of common glass. With a measuring wavelength range of 300nm–2500nm, this instrument can directly determine the UV transmittance of insulating glass without damaging its structure. Additionally, it features a spectral data export function, fully meeting the measurement requirements.

GlasSpec2500 Optical and Thermal Parameters Measuring Instrument

Prior to the test, it is essential to clarify the following: Ultraviolet (UV) radiation in sunlight with a wavelength below 300nm is almost entirely absorbed by the atmosphere¹. The UV radiation reaching the earth's surface generally only includes components with wavelengths ranging from 300nm to 380nm, namely UVA and part of UVB. Nearly all UVC encountered in daily life originates from lightning or artificial light sources², which is not within the scope of our discussion. According to glass databases, single-pane clear glass is also almost impenetrable to UVB radiation³, with a UVB transmittance of approximately 0.4%. Therefore, we can conclude that nearly all UV radiation transmitted through single-pane clear glass is UVA.

Below are the test results:

• Insulating glass (6mmClear+12Air+6mmClear) made with clear glass can block 52.56% of UV radiation;

• Ultra-clear insulating glass (6mmUltraClear+12Air+6mmUltraClear) blocks 24.48% of UV radiation but allows for 28% of UVB transmission.

The UV blocking effect of Low-E Insulating Glass

The table below presents the UV transmittance of different low-E insulating glass units (IGUs) and their corresponding UV protection performance (6mm Low-E+12Air+6mm Clear):

• Single-silver low-E IGU: 32% UV transmittance, attenuating over 65% of UV radiation;

• Double-silver low-E IGU: 15% UV transmittance, blocking over 80% of UV radiation;

• Triple-silver low-E IGU: 8% UV transmittance，over 90% UV radiation blocked.

These findings align with industry experts’ research results. Naturally, the glass samples selected in this paper do not represent all insulating glass. The data in Tables 1 and 2 are for reference only.

Conclusion：

The UV blocking effect ranks from strongest to weakest as follows: triple-silver low-E IGU > double-silver low-E IGU > single-silver low-E IGU > clear IGU > ultra-clear IGU. Low-E insulating glass can block more UV radiation and reduce the amount of UV rays incident on the interior.

References:

https://science.nasa.gov/ems/10_ultravioletwaves/

https://www.fda.gov/radiation-emitting-products/tanning/ultraviolet-uv-radiation

https://www.budgetblinds.com/la-verne-ca/community-connection/blog/do-windows-block-uv-rays/