I am trying to grasp some concepts, perhaps relativity forum would be better for this - sorry if so. My question is directed to all who are familiar with concept of wave–particle duality and Young's double slit experiment. Out of curiosity (and being too lazy to try and do the calculations myself), I tried to search the Internet and find out how many photons can a bulb emit in 1 second. Answers varied from 2.5 x 10^13 to 5.5 x10^32. Well, it doesn’t really matter (don’t think I don’t understand that bulbs may vary), but the point is, the number is definite. Huge, but not endless. For the sake of clarity, let’s assume that a given bulb emits a little smaller number of photons per second, say, 1 000 000 000. Now let’s assume that this bulb is being observed from a distance of 10 000 kilometers by numerous observers or observing devices. The devices are placed along the surface of a sphere surrounding the source of light. There is one device per every square meter, which adds up to total: The surface area A of a sphere with r = 10 000: A = 4πr^2 A = 1 256 000 000 This means there are about 1 256 million devices. Now, final assumption: imagine they are all capable of registering light from 10 000 kilometers away, and they are all pointed at our little bulb, which was turned on for 1 second and emitted 1 000 000 000 photons. What do the devices see? Does each 'catch' 1 photon, or is it only an average? What can be seen by the devices that have no photons left to observe?