sensitometer
Photography term: a device for measuring the sensitivity of photographic materials to light.
Measure the film sensitivity using a sensitometer.
actinometer
Physics term: a device for measuring the intensity of radiation, especially ultraviolet light.
Measure the intensity of ultraviolet rays with an actinometer.
Compound of 感光 (kankō, 'sensitization, exposure to light') and 計 (kei, 'meter, gauge').