Radiometer (noun)

1. A device for measuring radiant energy, especially light or electromagnetic radiation.
2. A type of electrical instrument that measures the rate of flow of electric or electromagnetic energy.

Origin:

Late 19th century: from radio- + -meter, on the pattern of spectrometer.

Examples:

1. The radiometer was used to measure the amount of light emitted by the sun.
2. The radiometer was essential in determining the properties of the new star.
3. The radiometer was a crucial tool in the early study of electromagnetic radiation.
4. The radiometer was used to detect and measure electromagnetic radiation from sources both on and off the Earth.
5. The radiometer was a key instrument in early experiments on light and color.