Although it's been covered already
I'll give it a shot. The reason that doesn't work is that your "light echo" is, in fact, a reflection. You experience that ever time you look into a mirror.

We can experience an echo because sound travels fairly slowly. Light travels at approx. 186,000 miles per second- far too fast for there to be an appreciable delay between transmission and perception of the reflection. (It can be detected, of course- but only by electronics that are far more sensitive than our own senses.)

Sorry, the theory doesn't work.
( The Resident Loon Not a demographic. Do not measure., Thu 3 Jul 2008, 13:10, Reply)