A few days ago one of the members of our local aquatic plant group had a 8 gallon nano cube tank, complete, except for a non-working light, to trade. I got it for a big batch of needle leaf Java Fern, that I needed to get rid of anyway. The tank is a reef tank, with a big filter compartment at the back, a 24 watt PC light, two cooling fans, and a couple of moonlight LEDs.
The PC light would give reef appropriate very high light, so my choice was to either use window screen to cut down the intensity or replace it. Since I would have had to buy a $20+ new ballast for it if I kept it I opted to replace the light with CFL Screw-in lights.
Here is the tank: (along with one of the bulbs I want to use, and the 2 socket adapter needed)
I stripped out the electronics, the fans, the reflector and it's shield, and the LEDs, leaving just the 120V wire and the bare top to work with.
This is the gutted top plus the 3 hole bracket I made from a piece of aluminum bar, to mount the light sockets. For a reflector I visited my local surplus metals store and found a bargain (as usual), some 12 inch wide, well polished, very thin hard aluminum sheet, for $1.50 a yard. I needed an 8" long piece, but that would have been too embarrassing to ask for, so I bought a yard.
I didn't want to get 100% of the light from the bulbs to the tank, to avoid having too much, so I decided on a simple reflector, with the sides at about 45 degrees to the bottom, two bends, easy to make with a shopmate work bench and a piece of wood. Then I drilled 3 holes (actually punched them out with a center punch) to match the aluminum bracket.
While I was doing this it seemed like a good time to evaluate reflectors for CFL bulbs, so I installed just the lights, no reflector, and measured the PAR at the bottom of the empty tank, getting about 25 micromols.
Next, I installed the reflector and secured the wiring, reinstalled the bulbs and remeasured the PAR, getting about 50 micromols!
50 micromols is right where I wanted it to be, low medium light. Here is how it looks with that light on:
My plan now is to work on the filter so I can use the tank for a high humidity riparium. Since I already had that double light socket, all I have spent so far is about $10 for the bulbs, and $1.50 for the aluminum sheet, of which I have almost all of it left over.