You searched for: “photometry
photometry
1. The measurement of the visible portion of radiant energy (light).
2. Measuring the characteristics of visible radiation (light); such as, its luminous intensity or illuminance, relative to standard references.
Word Entries at Get Words: “photometry
photometry
The measurement of the luminous intensities of visible light sources which is sometimes expanded to include near-infrared and near-ultraviolet light.

Photometric devices accurately measure the intensity of light from the stars and galaxies.

They are nearly all based on highly sensitive, light-detecting electron tubes, called photomultipliers.

In these devices, weak starlight causes electrons to be emitted from the surface of a photocathode, and each electron released can be made to produce many millions of secondary electrons.

This entry is located in the following unit: Astronomy and related astronomical terms (page 18)