Radiometry

Radiometry deals with the measurement and study of electromagnetic radiation, specifically focusing on the properties and behavior of light. It involves quantifying various radiometric quantities associated with the optical portion of electromagnetic radiation, which is further divided into ultraviolet, visible, and infrared.

Radiometry is important because it provides quantitative information about light and its interaction with matter. By accurately measuring these radiometric quantities, scientists can understand the physical characteristics and behaviors of light in different environments.

Radiometric Quantities

Radiometric quantities play a crucial role in accurately quantifying and analyzing various forms of radiant energy. The table below discusses these quantities.

Radiometric Quantity	Definition	SI Unit (Symbol)
Radiant Energy	Total energy emitted by a source in the form of electromagnetic radiation	Joules or J
Radiant Flux	Total amount of radiant energy emitted by a source per unit time	Watt (W)
Radiant Intensity	Amount of radiant flux emitted by a source per unit solid angle	Watt per steradian (W/sr)
Irradiance	Amount of radiant flux incident on a surface per unit area	Watts per square meter (W/m²)
Radiance	Radiant flux received by a surface per unit area per unit solid angle	Watts per square meter per steradian (W/(m²·sr))
Radiant Exitance	Radiant flux emitted by a surface per unit area	Watts per square meter (W/m²)
Radiant Exposure	Radiant energy received by a surface per unit area	Watts per square meter (W/m²)
Spectral Flux	Radiant flux per unit wavelength	Watts per meter (W/m)
Spectral Intensity	Radiant intensity per unit wavelength	Watts per meter per steradian (W/m·sr)
Spectral Irradiance	Irradiance of a surface per unit wavelength	Watts per square meter per meter (W/m²·m), or W/(m²·nm)
Spectral Radiance	Radiance of a surface per unit wavelength	Watts per square meter per meter per steradian (W/m²·m·sr), or W/(m²·nm·sr)
Spectral Exitance	Radiant exitance per unit wavelength	Watts per square meter per meter (W/m²·m), or W/(m²·nm)
Spectral Exposure	Radiant exposure per unit wavelength	Joules per square meter per meter (J/m²·m), or J/(m²·nm)

Applications

Radiometry is crucial in various fields, such as:

Astronomy and Astrophysics: Radiometry helps physicists analyze starlight or other celestial emissions to determine their composition and physical properties.
Meteorology: Weather forecasting or climate studies utilize radiometry to measure solar radiation reaching the Earth’s surface or quantify atmospheric phenomena such as cloud cover.
Photography and Cinematography: Proper exposure settings rely on accurately measuring the amount of light falling on a subject.
Others: It is used across industries like agriculture to optimize crop growth using artificial lighting, aerospace for thermal analysis, telecommunications, and fiber optics, among many others.

References
- 1. Radiometry and Photometry – Ossila.com
  2. Radiometry – Rp-photonics.com
  3. Introduction to Radiometry and Photometry – Andor.oxinst.com
  4. Radiometry – Cs.cornell.edu
  5. Radiometry and Photometry FAQ – Wp.optics.arizona.edu
  6. Radiometry and Photometry – Depts.washington.edu