It took *me* some time to understand what I had said two weeks ago :)

A cyllindrical light source is actually a spotlight but the spreading of
light is limited by a cylinder and not a cone. Putting one of these inside
the lighthouse would do you no good in comparison with point-, spot- or area
lights. However, if the beam does not illuminate any object, i.e. no shadow
is cast onto the atmosphere/media inside the ray, then one could place a
cylindrical light source on a large distance from the lighthouse and point
it *to* the latter and no one will notice the trick (if there's a bird in
the beam it will be obvious that the shadow is cast in the opposite
direction). The farther the light is, the better, since light rays will look
more and more parallel with the increase of distance, and that's the purpose
of a real-life parabollic mirror in a light house or a floodlight, after
which effect Mr. Fitzgerald is.

I hope I put it down more clearly this time.

Peter

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