Measuring Reflective Power with the Eye

Although the legitimacy of using the eye as an essential instrument in photometric experiments had been questioned by critics, the practitioners of visual photometry in the 18th and 19th centuries were convinced that the eye was reliable and capable of making accurate judgments in comparing brightness. They demonstrated their belief through their efforts in searching for the optimal conditions for the eye in photometric measurements. Eventually, they were able to measure reflective power with accuracy comparable to today’s standards by developing a body of practice, including both instrumental designs and experimental procedures, which aimed at maintaining the eye’s sensibility in brightness comparison.