Outside of physics proper (e.g., radiometry and computer graphics), there are even light fields. It has become a standard instrument in photometry and radiometry. HartRAO is used for continuum radiometry, spectroscopy, pulsar timing and interferometry. All modern TSI satellite instruments employ active cavity electrical substitution radiometry. REX performed radiometry of the nightside. Mandelis has created the field of dental photonic engineering and the technique of photocarrier radiometry. The site also has satellite tracking, telemetry, telecommand and radiometry facilities. Most properties of have been determined through photometry, spectroscopy, infrared radiometry, and radar imaging. In radiometry, radiant energy density is the radiant energy per unit volume. Radiometry is distinct from quantum techniques such as photon counting. Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. In radiometry, irradiance is the radiant flux (power) "received" by a "surface" per unit area.