 All right, so let's do a quick discussion of the sources of radiation, sources of light, and the surfaces that receive light in the lifetime of the photon, right? We know that from our little diagram technique that source of light, we diagram as a curved surface. We can diagram a straight arrow that's going to signify shortwave band light. We could draw a curvy arrow line that's going to signify longwave light. So right now we've got what is going to be a black body emitter that is emitting both shortwave light and longwave light, so it's probably a pretty high temperature surface, something like the sun, maybe around 6,000 K. And it's going to emit light. It's going to travel a long distance, somewhere along the distance. It's going to be transmitted through a transparent surface, something like maybe a window, the atmosphere, and ultimately it's going to meet its end, where it will be absorbed by some opaque surface, right? We're going to have something dark and opaque over here that's going to absorb the light. I've got these little dashed lines to signify absorbed light. However, if that material were heading in, say it went through the window again, we're going to hit a reflective material, something like a mirrored surface. We would draw that light bouncing off the surface, and of course it would not be absorbed by the surface. In reality, we have surfaces that do both things, that absorb some of the light and reflect some of the light, and we're going to have, use the symbol rho for reflectance, so maybe it is reflecting 30% of the light and it is absorbing 70% of the light. We would give these fractions from 0 to 1 to describe those percentages, but we certainly can do that in a quick diagramming technique.