Following publication, the author requested several small changes in paragraphs 2, 6 and 7 in order to better clarify the information provided. The original paragraphs, as published on October 15, 1998, appear below.
Paragraph 2
Scanning an image on a flatbed scanner involves passing a sensing
array (Charged Couple Device, CCD) along an object resting face down
on a glass platen. The array has a light source attached. Today
these sources are usually of the cold-cathode type (1) because of their color
characteristics and cooler operating temperature. The method is
similar to that of a photocopy machine. This has caused a
misinterpretation of the scanning process. Until recently, copy
machines used very strong light to produce an image on a relatively
insensitive zinc sulfide coated drum, which resulted in toner being
deposited onto paper. The amount of light needed was dictated by
the low sensitivity of zinc sulfide on the copy transfer drum.
Today's CCDs have sensitivities between 0.1 and 0.001 lux. (2) This means that a CCD does
not need blazingly bright light to achieve its goal. Scanner lamps
have evolved for a technology with greater light sensitivity.
Paragraph 6
Category 1 includes sensitive artworks whose members show just
perceptible damage, 0.01 
d, at 1.2
Mlx-hrs. This category would include early albumen prints, most color
photographs, Polaroid images, some watercolors, pastel or ink
drawings, works on newsprint, and a range of other non-paper
artworks.
Paragraph 7
Category 2 artworks are expected to sustain 10 Mlx-hrs of exposure
before showing just perceptible change due to non-UV light exposure.
Category 2 contains low stability paper-based materials, B&W
gelatin prints, and most slides. I would also include black
printers-ink engravings/etchings on average paper and documents
printed earlier than the 1850s with carbon ink on average paper.
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