Luminosity, brightness, and distance

In order to demonstrate the relationship between luminosity, brightness, and distance, I play the following game with my lecture hall students. In a darkened room, I screw a series of light bulbs into an empty socket at a fixed distance from the class. Each bulb has a different wattage, which I announce. I tell the students that I will place one of the bulbs into the socket a second time. They are to guess its wattage. The first volunteer contestant almost always guesses correctly. I then ask for a second volunteer. However, unexpected by the contestant, I illuminate a bulb with the wattage of one of the demonstration bulbs but located in another socket at the far corner of the room. Unlike the situation for the first contestant, the second contestant experiences one in which distance is ambiguous. He or she often gets the answer wrong. The class and I...