A few years ago I had some baseball cards on a shelf next to a window on a south wall. They never got directly hit by the sun but faded some after a few years.
I now have a desk right in front of a window on a north wall. There is no way it can get any direct sunlight but I’m worried that some cards I have on it will fade eventually. Should I be?
Any ultraviolet light (even light from fluorescent lamps) can cause fading. Reflected sunlight isn’t nearly as bad as direct, but if you are worried about long-term fading, you should use UV-blocking glass.
Sure. Doesn’t matter where the light comes from. I’m pretty sure that the fading effect depends on the total amount of light that has landed on the photo, regardless of whether it was bright light for a short time or dim light for a long time.
Also, the energy in each photon dictates what it can do to the chemistry of the object. Ultraviolet light is worst, then through the spectrum from blue to red, then infrared light least harmful. Each dye or other substance has differing sensitivities to each photon energy. While UV deserves its reputation for fading things, there’s also some advantage to choosing redder light sources like incandescent bulbs even if you are removing the UV.