Article: Light Levels Used in Modern Flatbed Scanners

On the IMAGELIB discussion list, Timothy Vitale wrote a long a thoughtful response to a question about digitizing rare negatives. In his response, he pointed to this 1998 article he published in the RLG DigiNews.

In the article, Vitale wrote:

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 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 light-insensitive coated drum, which resulted in toner being deposited onto paper. The amount of light needed was dictated by the low sensitivity of the coating on the copy transfer drum. Today's CCDs have sensitivities between 0.1 and 0.001 lux. 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.

So will light used to scan an item damage that items? Vitale says "no" and provides data to back up that claim. (He tested several machines and measured their light intensity.)

BTW in his conclusions, he provides good information for those thinking of using copystands to photograph works (the digitize the photos). If that is something you are considering, be sure to read the tips he provides.

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