We tend to associate fading caused by sunlight with the ultraviolet part of the solar spectrum. However, fading is also caused by daylight radiation too, so just knowing the UV transmittance (Tuv) of glass is not enough to predict fabric fading.

A more complete rating has been developed, the "damage weighted" fading function (Tdw). This value accounts for the combined damage caused by UV and daylight and it is considered a better alternative than just UV transmittance.

The chart on the next page shows that the Tdw for low solar sputter low-E glass is just about as good as anything available to reduce fading. Plus, the-low E is more affordable, also blocks solar heat gain, and adds insulating power to the window.