Historically speaking. (discovery of light sensitive materials used to record photographic images in the 18th century)

PSA Journal | July 1, 1993| | Copyright

Did you know that the physical effect of light on certain substances was known prior to the nineteenth century? Alchemists knew about the darkening of certain chemicals when exposed to light. Although the relationship between the exposure to light and the resulting change in color was known, the reason for the phenomenon was not understood nor pursued seriously.

Before 1850 all the known light-sensitive materials were sensitive only to light in the blue and near-ultra violet portions of the light spectrum. The sensitivity was restricted to wave lengths shorter than ...

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