What is the photometer?

What is the photometer?A. Testing picture Quality
B. Measuring light Intensity
C. Measuring Size of Picture
D. Checking colors and Pictures

A photometer is an instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Most photometers convert light into an electric current using a photoresistor, photodiode, or photomultiplier. Photometers measure: Illuminance. Irradiance.