In optics, photometry is the measurement of light's brightness, or luminous intensity. Photometry frequently focuses on the perceived brightness to the human eye. As such, it takes into account the eye's sensitivity to varying degrees of light and focuses primarily on the visible light spectrum.

In astrophysics & cosmology, photometry is the term used for the study of light emitted by a star or other astronomical object. This brightness is generally defined in absolute terms. Because astronomical objects frequently emit electromagnetic radiation in non-visible wavelengths, the more precise term for this is radiometry.

Also Known As: radiometry (in astronomy)