What are Radiance and Irradiance and how do they differ?

[JJ123]

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.

 

[mgb_phys]

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 )