Digital BW, The Print

I'm always delighted to read the comments of Mark McCormick-Goodhart who has over the years provided archivists with a number of highly innovative tools both for preserving images and for measuring those efforts at preservation. Knowing Mark's passion for this, I am confident that Aardenburg will continue that tradition of service to the imaging community.

Perhaps I was not direct enough in my comment ("abandoning the pretense of predicting lifetimes")to indicate that as an imaging scientist I think megalux hours (or some similar metric) is indeed a better way of providing imformation on light stability than years. 

None the less I also contend that it alone does not solve all or even most of the problems related to characterizing image stability or even just light stability. I mentioned some of the confounding variables in my earlier post. This is not trivial, and I have seen real world products where, for example, the choice of a light source for testing provided numbers that were meaningless in actual use evironments. (Fortunately, I have not yet seen manufacturers building to the test--which one could well do.)    

And even though we cannot find a useful way of integrating light, heat, humidity and pollutant degradation into one factor (something I have never suggested in my post or elsewhere), this does not mean that we can afford to ignore them. 

One of the other posters to this thread suggested that he would rather assume very high home light levels as a conservative measure. Fine. Assume 50,000 lux. Then you will almost guarantee that any other degredation process will be more likely to be the pratical cause of image loss in the real world. To repeat myself from the earlier post, balance as it occurs in user environments is vitally  important. 

One last comment. I don't want to sound elitist here, but the folks who post to this group understand a megalux hours metric--or if they don't, they will take the trouble to learn about it when it is called to their attention because they care about these things. 

Most consumers, however, neither understand nor want to learn about lux or ppm ozone or Arrhenius plots. They're understandably busy with other things. They want to know "How Long Will It Last" and they want that answer in years. Is it better to provide them with a number that has a large measure of uncertainty built in (perhaps better, a range)or to simply say nothing and provide no guidance at all. This is a debate that imaging scientists, conservators, and photographers have had for years (I commend to all a recent excellent article by Peter Mason of Torrey Pines Research on this issue--see their website). "Consumer Reports" and Wilhelm Imaging Research have done quite well by choosing the first alternative. Aardenburg serves a different audience. 

However, if we do choose to provide a years metric for some users, then we must base on the the best scientific data we can gather, not guesses or assumptions or personal beliefs. On that point, I won't back down.