Find any article(s) online that explains the idea of radiance. In your own words, what is radiance? Draw a small diagram that helps illustrate your explanation. [Note: you are free, in fact encouraged to discuss this question with your classmates!]

Suppose you have just implemented a photorealistic renderer, and everything is looking pretty good. However, when you go to move the camera closer to the scene, you notice that everything gets darker. In particular, moving the camera closer by a factor 1/2 makes the scene darker by a factor 1/4. What might have gone wrong? In particular, which radiometric quantity might you (mistakenly) be computing, and which quantity should you be computing? [Hint: think about the "number of hits" seen through a given pixel.]