I give credit to "snooze" for this idea and it works great.

Use a mason jar as your enclosure.
Drill a hole in the centre of the metal top
where your wire will go through. Use a 20 Watt
halogen bulb and if you wish add some coloured filter at the
bottom of the jar (where the light will shine through).
Silicone both sides of where the wire goes through
the hole on the metal top and attach the wire to the bulb
by any means (I soldered mine).

Wait at least 24 hours for the
silicone to dry. Before sealing the jar add some pebble rocks for
weight so the jar sinks to the bottom. Seal the jar up with the top and
ring. You can line the inside of the jar with aluminum foil to give the
light more direction.

Note: Use a DC wall adapter for power with 1 - 2 Amps output.
ie: 12 volts DC with a 20 watt bulb