I'm looking for a technical web page, that I can relay to a friend, explaining the physics behind why a large head (reflector, really) on a flashlight provides more "throw" compared to a smaller one. Anyone know of such an URL I can pass along?
[Unfortunately, links to discussions on this forum, or other similar forums, blogs, etc. wont be of any use in this case. He insists it be from more of an academic source like a text book or a scholarly journal, I guess.]
I would imagine this is explained in text books on physics, and that's exactly what I'm looking for, but I don't know where to find such references and I was hoping some of our readers here might know.