Floating Tank Light

I'm proud of myself - especially since I am not a handyman. Here, for what its worth, is how I built my <floating> narrow aspect light fixture for my new 36x12x17 high fish tank. Thanks to the plant list, the news groups and the FAQs for help and ideas. Comments and suggestions will be welcomed.

I wanted to use four 48 inch GE Trimline T-8s to get 128 watts for this 30 gallon tank. Had read here that 2-5 watts per gallon is a good rule of thumb for growing plants. I also remember that the 128 watts fit in the ballpark of Axelrod's 25 watts for 100 square inches at 12 inches test for surface area and depth. The 128 is a little more than I actually get since I've got 6 inches of lamp hanging outside (not over) the tank on each end. But maybe its shining through the tank ends a little, too.

These GE lamps are 32 watt RE 850 Phosphor F32T8/SPX50 which burn (glow?) at 5000K and 80 CRI. Each is supposed to throw 2800 initial lumens and 2520 mean (lifetime) lumens. Grainger 1G946 at $7.41 each.	

My tank opening is 10.5 inches wide (after considering the top trim) and with the Marineland Emperor filter hanging on the back, I have only 8.5 inches to work with. I looked for a fixture that packed 4 T-8s close enough together to fit over my narrow tank. I couldn't find one and thus decided to build my own. 

I picked the GE/Motorola electronic ballast G4INT8 for $40.95. It is made to drive four lamps. Although it is not very heavy, I wanted to hang this ballast on the wall remote from the fixture.

My <fixture> is a piece of scrap pine (old shelf) 1 x 8 x 50. I attached screw mount lamp holders (Grainger 5C403 package of 10 (two left over) for $15.50) to the board marking their positions with the lamps in place. Figured I didn't need the water resistant type since I use a cover glass. Bought wood screws to mount them since the included mounting hardware was for sheet metal. Made a shade on the front and the ends with some light lath 1/4 x 3 inches. Should have picked the short lamp holders instead of the long.

I also should have left space between the two pairs of lamps to allow for the rubber/plastic hinge in my cover glass. Didn't and just snugged up the four lamp holders all together. The 1.25 inch hinge is blocking some of the light. The way I did it the four lamps are only 5.5 inches wide, though. 

Because I used a wood fixture, I was told I needed to put some grounded metal near the lamps. I don't understand the physics of this, but I stapled some aluminum window screening and one end of a wire to the board. The other end of the wire went to the ballast case. There is no reflector - yet. Don't see why I couldn't put some reflective mylar over the screening. I don't think it would stop the field or whatever magic the metal screen is doing

I grounded the ballast case to the center post on the wall outlet and wired the lamp holders to the ballast per the diagram on the ballast. I used sixteen gauge solid core wire per the directions on the ballast. I was told later I should have used heavier wire (12 gauge) because of my 10 foot run between fixture and ballast. The 16 works fine though. 

What a mess all these wires were! There were seven connections to the ballast from the fixture. Two wires ground each of the two pairs of lamps. This plus a  feed for each of the four lamps and the grounded screen door make seven. I used masking tape on the running ends to mark which wire was which since I had bought 30 feet of a red and white twisted pair. (This was more confusing than you might think. Get four different colors of wire if you can.) I used black electrician's tape every few feet to bundle the wires. I want to get one of those flexible plastic conduit-type things that Officemax sells to manage computer wires. These are slit end-to-end so I can slip in on over the bundle without removing the wires. I hope.

The <floating> part: I hung this rig on quarter inch nylon cords from two little pulleys hanging from hooks in the ceiling. Made a little yoke on each end of the board - attaching each yoke with two screw eyes. Small weights from a weightlifting set (I should be using) are on the ends of the cords. When the weights are on the ground the fixture is in its highest position for tank maintenance. I lift the weighted cords to lower the fixture into its plant-powering position. Its not perfectly counterbalanced, but the friction of the cords on the ends of the board lets me stop it at any height. This is a alternative to the piano hinge method described by Geo. Booth for his tank access. I figured with this narrow tank I needed all the room I could get for my big mits.

Well its blindingly bright and I'm happy! Now I guess I need some plants - and to get to my welder's supply house and to dive into the intricacies of fertilization and micro nutrients so intricately discussed and debated here. I suppose some fish would be nice for this fish tank, too.