Radiometry is the study of how energy travels through space as electromagnetic waves and how we can measure and analyze this energy to understand more about the world around us.

  • Radiometry studies the properties of electromagnetic radiation (intensity, spectral distribution and polarization) and how light interacts with matter (absorption, reflection, and scattering).
  • Electromagnetic radiation and the electromagnetic energy it transports can be described in terms of waves.
  • Electromagnetic radiation can be described in terms of photons and their properties.
    • Energy: Photons have energy that depends on their frequency or wavelength. Higher-frequency photons have more energy than lower-frequency photons.
    • Number: The number of photons in a given electromagnetic radiation depends on its intensity or brightness. Higher-intensity radiation has more photons than lower-intensity radiation.
    • Direction: Photons travel in straight lines, but their direction can be changed by interacting with matter.
    • Polarization: Photons can be polarized, which means that their electric and magnetic fields oscillate in a particular direction.
    • Speed: Photons travel at the speed of light, which is approximately 299,792,458 meters per second in a vacuum.
  • Radiometric techniques characterize the distribution of radiant power (transfer of energy per unit of time) in space.
  • Radiant power, also known as radiant flux, is the amount of energy emitted by a source of electromagnetic radiation per unit of time. It is typically measured in watts (W) or in other units of power such as ergs per second (erg/s) or joules per second (J/s).
  • While radiometry deals with electromagnetic radiation, photometry deals with the interaction of light with the human eye.