Photometer

n. device used to measure the intensity of light

In the broadest sense, a photometer is any instrument used to measure illuminance or irradiance. As applied in industrial photometry, a "photometer" is the general term covering instruments for detecting:scattered light intensity absorptionfluorescenceMost photometers are based on a photoresistor or photodiode. Either exhibits a change in electrical properties when exposed to light, which can be detected with a suitable electronic circuit.
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Noun
1. measuring instrument for measuring the luminous intensity of a source by comparing it (visually or photoelectrically) with a standard source
(hypernym) measuring instrument, measuring system, measuring device
(hyponym) spectrophotometer
2. photographic equipment that measures the intensity of light
(synonym) light meter, exposure meter
(hypernym) photographic equipment
(hyponym) cytophotometer

n. (new spell.=Fotometer) photometer, device used to measure the intensity of light

(n.)
An instrument for measuring the intensity of light, or, more especially, for comparing the relative intensities of different lights, or their relative illuminating power.