Luminance, Light and Ray

This was an interesting reading. For the most part I understood what the <> were doing, however at first I was a little unsure if I should be reading them or not. It was interesting to see the different ways of explaining luminance, light and ray. One of my favorite parts throughout the reading was the part he talks about luminance in reference to animals that glow. Not only how do they glow, but do they really glow throughout the day and we just can't tell because it's light out, or do they stop glowing throughout the day and only glow at night. Depending upon the surrounding background and it's value of "darkness", you can see the animal glowing easier. Do they have a weaker glow during the day and use less energy, or do they use the same amount all the time?