Kathleen:
 
It is often much more productive to shell at night, particularly for
sand dwellers and some cones.  In Samoa it was interesting that the sea
snakes were very attracted to your light and with only 6 inches of water
under you it is more interesting.  About the only way to get rid of them
was to turn off the light.
 
Also, depending on where you are, shells tend to come out en mass just
after the tide starts coming back in after low tide.  In New Guinea the
miters were very pleantiful on one island at that time. On another
island they were plentiful near low tide in about 2 - 3 feet on a
steeper sand beach. In Bohol, Philippines, on a sandy beach with a very
gradual slope, small olives and nassarius were very pleantiful at very
low tide, in puddles just above the water's edge.
 
If you are going far, getting back when a light fails (I had two failure
on a Thailand trip) is also interesting.  The comment on carrying a
spare is really very well advised.
 
Aloha,
 
Wes