SPFG, Supreme Picture Framing God
Not so, Jeff. "The rest of the spectrum" consists of visible light and infrared light, and all of it is damaging. As far as I know, nobody from any manufacturer or testing agency has suggested that UV radiation is the only source of damage, nor has anyone suggested that UV filtering stops fading. That myth has been perpetuated only by framers who are either uninformed or purposely devious.Sort of like when you choose a very small target spectrum and declare 99% protection while failing to mention the rest of the spectrum.
In any case, let's not get muddled up in myths or Mad Science. The facts are clear. Ultraviolet (UV) radiation, about 300 to 400 nanometers, has been proven more harmful than other wavelengths to inks, papers, and other materials used in framing. More than other wavelengths, UV radiation advances aging and deterioration, which commonly shows up in framing as faded colors, acid creation, and weakened fibers in paper and fabrics. Since it is the most harmful and we can not see it, removing as much of it as possible is beneficial. For most manufacturers and testing agencies in the framing industry, the actual range of measured UV filtering seems to be standardized at 300 to 380 nanometers. The narrow band from 380 to 400 nanometers is difficult to measure, since the transmission curve changes from near zero to near 100% very steeply.
Remember ROYGBIV? Red, Orange, Yellow, Green, Blue, Indigo, Violet are the colors in the visible light spectrum that carries an image to our eyes, so it is beneficial to transmit as much of that light as possible. Ordinary glass transmits about 91% of it. 2.5 mm Museum Glass transmits more than 97% of it and reflects less than 1% of it. At about 99% transmission, 2 mm water-white glass products transmit less than 1% (99/97) more of visible light.
Infrared (IR) radiation, about 700 to 1500 nanometers, is harmful as well, but in a different way. In a picture frame, IR mostly causes increased molecular activity, which generates heat and amplifies the effects of UV radiation, accelerating degradation of materials, such as colors and paper/textile fibers.
It isn't rocket science, it isn't mystical, and it is unfortunate that some want to make it confusing. Read the manufacturers' published specifications, read the standards of scientists - conservators and testing agencies, then make your choices.