What are Radiance and Irradiance and how do they differ?

AI Thread Summary
Radiance refers to the power emitted from a source per unit area in a specific solid angle, while irradiance measures the power received on a surface per unit area. The key difference lies in their focus: radiance describes energy output in a direction, whereas irradiance quantifies energy input onto a surface. Understanding these concepts is crucial for fields like optics and photometry. Simplifying the technical definitions helps clarify their distinct roles in energy transfer. Clear definitions enhance comprehension of these important physical concepts.
JJ123
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Hey, I'm having trouble working out what Radiance and Irradiance are, all the definitions I get are along the lines of something really technical like:

"For a point of radiant energy, Radiant Intensity, in a specified direction, per unit projected area: Le=(dIe/dA)*Cos(theta) where A is the area and theta is the angle between the specified direction and the surface".

Would you be kind enough to give me a very simple wordy definition of what these are and the difference between the two? Thank you SO much.
 
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Radiance is the power from the source per area into a certain solid angle.
Irradiance is the power onto a surface per area

(hint, Irriadiance = I = input )
 
So I know that electrons are fundamental, there's no 'material' that makes them up, it's like talking about a colour itself rather than a car or a flower. Now protons and neutrons and quarks and whatever other stuff is there fundamentally, I want someone to kind of teach me these, I have a lot of questions that books might not give the answer in the way I understand. Thanks
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