Here we are going to turn 3 cheap ($4 each at fry's marketplace) LED screw-in lights into a fishtank light/hood combo.
Step 1: Break lamps
Break lamps carefully. Wrap lamp in towel, make note where glass is (don't hurt the leds when breaking) break using pliers, not a hammer. You don't want to damage leds.
Step 2: Design your led layout in Illustrator
design your led layout in Illustrator. you want to make a natural pattern, not a silly inefficient human square pattern. go in 60° and 120° angles to make hexagon shaped layout, and space them out for your dimensions evenly using the distribute function. My 10g tank's top is 19.25 x 9.5 inches. I had 60 leds to work with, so i went with 6 rows of 10.
Step 3: Mark out sheet metal, drill holes.
Buy galvanized sheet metal at home depot (about $30 for huge roll = most useful thing you can buy for diy)
mark out your led layout using sharpie and ruler.
drill holes - make sure you measure the led's diameter - not the wider lip part, but the thinner part. that way they will sit nicely in drilled holes and not fall through. my led's measurement was 4mm, or about 0.15" inch which is just over an eighth of an inch.
this is what your drill bit should be. if you don't have one this size, you can do smaller holes like i had to then gouge them out using knife to be perfect size, so when you poke led through it is snug, and won't fall through.
wipe whole sheet or just hole areas on both sides with acetone to aid adhesion of ...um, adhesive?
lay dow sheet and after snipping off leds from base circuit bend their connectors 90°.
Arrange all leds (you are gonna have 3 sets, going in a loop), and glue down using whatever you prefer. i chose quick set clear epoxy because it sets 100% faster than silicone.