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In 1888, Ferdinand Hurter and Vero Charles Driffield patented a device for estimating the actinic power of sunlight and for computing exposure times and apertures for cameras, based on the plate speed, time of day, time of year, and latitude.
The study has its origins in the work by Ferdinand Hurter and Vero Charles Driffield (circa 1876) with early black-and-white emulsions.