From: "Bob Blakely" : On the macro scale (above the scale of particle physics), intensity drops : off as the square of the distance for all electromagnetic energy, including : light, all the time, everywhere in the universe. It's the law. No : exceptions. just a quick interjection - this rule applies to a point source light, no debate whatsoever but unfortunately it doesn't apply when a lens or collimator of any desription is involved. as an extreme example to contrast with a point source light is a laser where the power doesn't drop with the same relationship to distance. the best relationship to look at when talking about enlarging is the size of the image on the baseboard - if the image has 4 times the area then any given section of that area is only receiving 1/4 of the light intensity as before.. the relationship to height will still be there but it's more complex than the straight iverse / distance law karl
