General view of technician James Geary using a Klett-Summerson Photoelectric Colorimeter to obtain a determination of iodine at a Dow Chemical Company laboratory. Designed in the 1930's by two Cornell University Medical College students, Arnoldus Goudsmit Jr. and William Henry Summerson, the Klett-Summerson Photoelectric Colorimeter was manufactured and sold by the Klett Manufacturing Co. of New York beginning in 1939.

Photoelectric colorimeters measure the absorption of particular wavelengths of light by a specific solution, i.e. the solution's color. The precise quantification of color is then used to derive more information about the solution, most commonly its turbidity (the cloudiness or haziness of a liquid due to the presence of suspended particulates generally invisible to the naked eye) and/or the concentration of a known solute.