I wanted to build a powerful dive light that didn't cost the earth but I don't have access to a CNC or metal lathe so I thought I'd see if I could 3d print one. This is designed to house the 25W, 50W or 100W LED's that you can get cheaply from china or ebay with a 50mm reflector and 44mm collimating lens (you can buy them all from deal extreme or banggood). The front lens is 8mm polycarbonate from Bunnings (or any hardware store) and the rear is 5mm aluminium plate, both sealed by 63mm ID 2mm cross section o-rings. The battery and LED driver are in a separate waterproof enclosure of your choosing. So far I've left this thing switched on in the sink for an hour and been for a quick snorkel and it definitely works and is super bright with a wide beam, see crappy photo. I'm yet to take it down to any depth to really test it though.I printed the body solid with 5 perimeters - you don't want any air in there if you can help it. This makes for a pretty solid chunk of plastic that seems to be pretty strong and watertight. You'll need to cut 40mm radius discs of the polycarbonate (or some other form of clear material and 5mm aluminium with 8 evenly spaced 3.2mm holes with their centers in a 36.75mm radius. You'll also need to cut another piece of aluminium in the shape of the LED but with one of the flat sides coming only to where the yellow LED starts (this is to allow room for the cable gland retaining nut, drop me a line if this doesn't make sense). I used a jig saw and drill press, a water jet cutter or CNC would likely work better. Other bit's you'll need are: Assembly is straight forward. Solder leads to the LED first. Glue the smaller piece of aluminium to the back of the LED and then glue the assembly to the centre of the aluminium disc (you might want to pre-drill the hole for the cable gland). This provides a good sized heat-sink that will be in contact with water, so no worries about heat build up. Screw or glue your cable gland and switch into the aluminium, making sure it fits into the back of the body ( I used some JB weld). Thread your cable though the gland and connect to the LED, then tighten the gland to make it water proof. Insert the the lens retainer, then lens then reflector into the printed body. Bolt the whole thing together with the o-rings in the obvious places and there you go. Note that I used acetone to smooth the o-ring grooves before bolting together. The handle mount needs 2 M5 nuts inserted then the thinner plate glued on top then the whole lot gets glued to the light body. The handle (modified from yakwool's keyhole saw handle) then bolts on using 12mm M5 bolts. There's also a goodman handle I can upload if anybody wants.