Anyone have observations on the effect of direct sunlight on film?

[loccdor]

Sometimes when I am drying film and going through the negatives/positives before cutting them into strips and filing them away, I will hang them by a window that gets some sun. They don't stay there long, from a day to sometimes a week.

It got me wondering, does anyone have observations on the effect of UV light on film, to get an idea of the time and intensity of light it would take to have a noticeable impact on the images. Would certain types of film be more affected than others?

Also, does the artificial light and heat from a slide projector degrade them over time?

 

[dpurdy]

Do you use pyro? I had the distinct impression once that after leaving a Pyro processed roll of film on my light table that was usually on for a couple of days, the stain had bleached away to some degree. So I never do that now. Silver is known to fade in sunlight, I think. But it would take awhile.

 

[loccdor]

Do you use pyro?

Yes, sometimes. That is interesting, thank you.

 

[khh]

Well processed film should be pretty stable, but I would expect sunlight to increase deterioration of the film. The gelatin would get brittle quicker, and the dyes in colour film would start to fade. Behind a glass window, rather in direct sunlight, I would expect these effects to be negligible if it's just a day. Probably a week too. But in direct harsh sunlight that would be enough time to see an effect, probably.

 

[koraks]

Would certain types of film be more affected than others?

Color film is inherently sensitive to UV and heat. I would certainly not recommend hanging your color film in sunlight for a week, although the effect will likely be marginal. A light table won't do much damage, at least not within a couple weeks' time.

 

[jmrochester]

A light table won't do much damage, at least not within a couple weeks' time.

I'm not sure this is correct. Many years ago a work colleague left a number of color negative strips in an overlapped bunch on her light table for hours/days. When I got mine back, a faint image of other negatives was visible on mine, making my negatives unprintable. Because image dye loss was not the likely explanation, a hypothesis was suggested that it was due to bleaching of retained spectral sensitizing dyes. I don't know if this is a concern with current C41 films, but I guess I would avoid unnecessary lengthy light exposure just to be safe.

 

[reddesert]

Also, does the artificial light and heat from a slide projector degrade them over time?

It is well known that the light from a slide projector degrades slides (yes, even/especially Kodachrome). For average amateur use, any given slide isn't projected for very long, so slides can last a long time, but a slide that sees a lot of use ideally would have had a projection duplicate made. (This may not have much relevance any more since slide projectors have much less commercial / industrial use than they once did.) For example, from Henry Wilhelm's book "Permanence and Care of Color Photographs" : http://www.wilhelm-research.com/pdf/HW_Book_06_of_20_HiRes_v1c.pdf