This article is devoted to building a simple metal halide lighting hood for a reef tank (or any thing else that needs a lot of light). You should be comfortable with wood working and basic wiring before attempting this project.
This project takes about a weekend to complete and makes a hood for a tank that measures 24″ x 13″ (about 20 gallons). The dimensions can be adjusted to fit any tank.
Things you will needs
Before you begin, assemble the following items to complete the job:
- Table Saw
- Jig Saw or Saber Saw
- Carpenter’s Square
- Tape Measure
- Wood Clamps
- Paint brush
- 4′ x 4′ x 3/4″ Sheet of Plywood
- Hinges (2)
- Cabinet Knob
- Fan Cover
- Mogul Socket and Bracket
- MH Ballast
- 1″ Wire Clamp
- Magnetic Door Latch
- Polyurethane clear coat sealant
- 4 – 2 1/2″ #6 wood screws
- 1/4″ wood screws
- 1 pound 6 penny galvanized finishing nails
- Wood glue
- 6′ 2 conductor 18 AWG wire
Cutting The Wood
Now that you have assembled the items, it’s time to start cutting the wood. Start by laying out the basic peices on the plywood. We’re going to need the following sizes for this project:
- 2 – 24″ x 9″ (Front and Back)
- 2 – 11″ x 9″ (Left and Right)
- 1 – 13″ x 24″ (Top)
- 1 – 19.5″ x 7.5″ (Door)
Below is a picture of the basic layout for cutting.
It’s very important that the edges of the pieces are straight and square. Your hood will end up being lopsided if the pieces are not perfectly square.
Once you have cut the pieces, assemble them for later use.
Building the Hood
Using the pieces of wood cut above, assemble the front, back, left and right pieces into a box. Clamp the pieces and then nail the box together. A little glue on the joints will make a better seal. The box should look like this:
With the shell of the hood completed, place the top on the box, nail and glue the top in place.
The following steps are optional, depending on the use of the hood. If you plan to sit the hood on the top of the tank, you’re going to need some way of getting into the tank. To accomplish this feat, we’re going to cut a hole in the front to create a door.
It’s worth noting at this point that if you don’t plan on having a door, you only need a 4′ x 2′ sheet of plywood. Simply align all the pieces vertically on the sheet, and remove the door piece from the picture.
To cut the door, make a mark 2 1/8″ in from each side and 1 3/8″ down from the top of the hood (measured from the border of the front, not the outside edge of the hood itself). Mark a square indicating were the door will be, as shown below. The use of tape will minimize the amount of splintering during the cutting process.
Clamp the hood down and make the cut with the saber saw. Round out the corners during the first pass, and then make them square with a second pass. The final product should look like this:
Once again, we have a choice in our design here. If you are going to put a large wattage metal halide lamp in this hood, is it best to have a fan to keep the hood cool. If you are going to use flourescent lamps or don’t wish to have a fan, you can skip the next few steps.
On one of the ends, the choice is yours, mark an X indicating the center of the end. You can do this by aligning your level with the top corner on one side, and the bottom corner on the other side. Do this for each side. Next, using the fan, trace the outline of the circular fan compartment. The marks should look like:
Drill a hole in center of the circle, and use the saber saw to cut the circle from the side panel.
With all the piece cut and put together, it’s time to “finish” the hood. The first step in finishing the hood is to seal the wood from the moisture of the tank. You have a myriad of choices here. I chose to use only polyurethane clear coat for my hood, but you can use a stain followed by a clear coat if you like. It is important that you put at least 2 coats of sealant on your hood to protect it from the moisture of the tank. Also, you should seal the inside and the outside.
Here are some pictures of the finished hood:
With the finish applied, go have a beer and and relax 😉
Once the finish is completely dry, attach the door to the hood using the hinges. Drill a hole in the center of the door, about 1″ up from the bottom. Place the door knob where the hole is.
Now that the finish is dry, it’s time to install the reflector. It’s best to leave some room between the top of the hood and the top of the reflector to allow for air circulation. Thus, the first step is to insert spacers on the top of the hood. You can use any wood as the spacer, but if you choose to use plywood, please ensure that you screw into the finished side, not the plywood side. Otherwise, the wood will split. You should predrill the holes for the spacers to ensure the wood will not split. Also, make sure you don’t screw through the top of the hood when attaching the spacers. It’s best to counter tap the screw holes. I used some wood I had laying around for the spacers (the second attempt anyway). It was about 1/2″ thick, so I used 3/4″ woodscrews and recessed the heads.
With the spacers in place, put the reflector in the hood and ensure it is centered. Screw the reflector into place.
Insert Fan and Socket
Prior to adding the fan, drill a 1″ hole in the top corner of the hood for the fan and lamp wiring. The hole should be 1″ from the top of the hood. Insert the wire clamp into the hole and screw into place.
To insert the fan, we must first figure out where to drill the holes for the fan. To do this, center the fan on the outside of the hood, over the fan hole. Align the inside rim of the fan with the edge of the hole. Once this is done, take one of the fan screws and push the screw into each of the 4 corners of the fan, marking the place where the fan screws need to be.
Drill a pilot hole for the fan where the marks indicate using a 1/8″ drill bit. I couldn’t find any #6 machine screws that were long enough to attach the fan *and* the fan guard to the hood, so I improvised. I attached the guard to the outside of the hood using 1/4″ wood screws, and I attached the fan to the inside using 2 1/2″ wood screws. This worked perfectly.
With the fan in place, attach the MH socket to the reflector using 1/4″ wood screws. It’s best to drill pilot holes using a 1/8″ drill bit. Feed the MH wiring through the hole in the top of the hood.
Next, attach the fan wiring to the 2 lead cable, as shown below.
With the wiring complete, tighten the wire clamp to fix the wires in place.
Next we have to attach the door latch to our hood. Each hood will be a little different, but most this should work for most of them. Make a small block of wood for the latch to rest on. Attach the block to the hood on the inside near the bottom of the hood. Then attach the metal flash plate to the hood door so that it will make contact with the latch when the door is closed.