Confusion over concept of 'radiance'.

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SUMMARY

The discussion clarifies the concept of 'radiance' in radiometry, emphasizing that it is defined as radiant flux per unit area per unit solid angle (steradian). Participants highlight the distinction between related terms such as radiant energy, radiant energy density, radiant flux, and irradiance. The confusion arises particularly around the uniformity of radiance along a ray or beam, which is confirmed by the referenced literature. The Wikipedia article on radiance serves as a reliable resource for further understanding this concept.

PREREQUISITES
  • Understanding of basic radiometry concepts
  • Familiarity with terms like radiant energy and radiant flux
  • Knowledge of solid angles and steradians
  • Basic principles of light propagation
NEXT STEPS
  • Read the Wikipedia article on 'Radiance' for a comprehensive overview
  • Study the relationship between irradiance and intensity in radiometry
  • Explore the mathematical derivation of radiance uniformity along a beam
  • Investigate applications of radiance in optical engineering
USEFUL FOR

Students and professionals in physics, optical engineering, and radiometry who seek to deepen their understanding of light measurement concepts and their applications.

genxhis
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I have some confusion about what 'radiance' means as used in radiometry; specifically, I don't understand what it is a function of. For example: radiant energy is specified over some region, radiant energy density is specified at a point, radiant flux is specified across some surface, Irradiance -- often called intensity -- is specified either across some finite surface or at a point in a given direction (by taking an infinitesimal area normal to the given direction), and intensity -- adopting the SI definition -- is specified along a line from a point-like source. But radiance? I don't understand. I became especially confused when my book tries to prove that 'radiance' is uniform along a ray or beam. All I really know is it is measured in flux per unit area per unit steradian.
 
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