The problem with any extrapolated test, be it Wilhelm's method, which is decidedly harsh, or Kodak's, which is not really a longevity test at all, is that neither one really tells you anything.
Wilhelms method tells you tat if you pump 450 lux into a print for 12 hours per day, it will start to fade after X number of days. Nothing else. Nada. His methods don't reflect how prints are treated in the real world, and cannot be used to judge anything, beyond comparing how different materials react to his testing procedures. Regarding cost of 100 speed film to 800 speed film, I doubt very much if it costs more to make one than another, at least not an appreciable amount. William Robb
