A photometer is a tool scientists and photographers use to measure light absorption, illumination and light intensity, and there are many different types. In general, the person using the tool gets the same illumination after locating the two sources, and the illumination is equal on two adjacent surfaces.
The different types of photometers include a built-in photometer, a spot photometer, a color photometer, a handheld photometer and an incident light photometer. In photography, photographers can better deal with light radiance variances by allowing them to control and set their exposures. This is true for even a single photographic subject, including items and people.