"Joe Pylka" wrote in
ink.net:

How confident are you that you know for sure where
the boat that's going to hit you is coming from, so you can point your
light toward it?

Good question. A visible signal is only good if someone is looking in the
right direction. A few years ago about 10 of us were on a small lake for a
moonlight paddle. All but two had headlamps. We saw a boat approaching so
everyone looked in that direction and started shaking our heads so that the
boat operator could see us. When it got to about 200' away I realized that
they were not looking in our direction so I blew my very loud whistle. That
got their attention immediately and they veered off.

If you're going to paddle at night (or anytime when there is a lot of boat
traffic) carry a loud whistle.