Help! Can light coming through old stained glass windows discolor upholstery?

[Meryl]

Hi Everyone,
My house was built in 1926 and is the proud bearer of 4 beautiful stained glass windows. I purchased a new sofa 3 years ago and over the past year, certain areas (turns out those closest to one window) have turned reddish and upon close inspection one small spot has taken on a green cast. The closest stained glass window has a lot of pinkish and green glass. At this point I am certain that the window is the cause; before I recover the sofa I would like to figure out (a) how/why this happened; and (b)whether I can prevent it from happening to new upholstery.
Thanks,
Meryl

[Rebecca]

Sunlight fades most fabrics.  There is nothing that stained glass adds to sunlight; on the contrary, it takes some of the wavelengths away from sunlight.  So it isn't the stained glass that is changing your upholstery; it is the sunlight.

Rebecca

[Richard Gross]

Rebecca is absolutely right; it's the UV light in the sunlight that discolors fabric, or most everything for that matter. Glass, colored or clear, actually filters some UV and slows the process.

When you recover the sofa, you might consider an UV-inhibitor. (for example: http://www.sbifinishing.com/uv.html).

[Meryl]

Thanks to both Rebecca and Richard for your responses. I have one follow-up comment. The upholstery is not faded as much as discolored; the areas where the green stained glass casts green on the upholstrery have actually turned green and the areas where the pink light falls on the upholstery have turned reddish.  Areas of the sofa further from the stained glass window (but exposed to light through a clear window) are slightly faded, but not doscolored. I have removed the slipcover and moved it out of my living room (even brought it back to the furniture store to show them) and it is clear that the red and green discoloration is real (i.e. not an artefact of looking at it in the room where the stained glass window is located).  Has anyone ever heard of this seeming transfer of color from the window to upholstery?
Thanks,
Meryl

[Rebecca]

There is no way the color can transfer from a window to upholstery.  I think you have a poltergeist.

Rebecca

[Richard Gross]

Since I haven't seen the fabric, all I can do really is speculate. However, I think there are two things worth considering. The first is this: as Rebecca said, color wouldn't transfer from the window to the fabric; however, some fabrics can take on different color casts as they fade. Browns can tend to become reddish, for example, because of the elements of color that make up the brown dye.

The second thing worth considering is this: light through a stained glass window tends to move fairly dramatically because the window moves relative to the light source -- the sun -- throughout the course of the day and throughout the year. Thus, an interior point that receives red light at one point might receive blue light later in the day, and no light later in the year as the viewed position of the sun in the sky changes. Unless it's a monochromatic window lit by artificial light, the color of light cast and the places where that light is cast have to change fairly steadily.

[Meryl]

Thanks again to both Richard and Rebecca. The fabric is light brown so the reddish hue makes sense (it doesn't explain rhe green spots where the green light is cast), but I am going to make sure that once my new upholstery is on, that I either regularly rotate the cusions or rearrange the room so that the sofa is further away from the stained glass.
Meryl