I have had my 55 gallon aquarium for half a year now and wondered "what do my fish do after the main lights go off?" I began searching the internet and came across the idea of using dim blue light to simulate 'moon lighting'. After I took a closer look and dug deeper on the web, I discovered that they were just blue LED's. Simple enough I thought. That led me to begin designing my own. This instructable focuses on the 'kit' style hoods. If you have a different style, you will have to find a different way to mount the LED's.
Make sure that you read through the entire instructable before you start.
Step 1: Planning
Once you have decided to build these lights, you must decide how many LED's and which ones you will use. I went with 8 LED's, 4 in each hood and it turned out perfect. Determine which LED's you will be using and what your power source will be. The LED's I used were rated for 2.8V@20mA. My power source was an old wall wart that was rated for 6VDC@100mA. Make sure to actually test the voltage coming out of the supply as mine was up at 9.9V! Don't forget that when you work with LED's you need to limit the current by using resistors in the circuit. You could do all the math, but being lazy, I used this site and it worked awesome, just plug in your numbers and it does the rest.
Now you have to determine how to mount the LED's. I simply drilled holes for the LED's in the existing fluorescent mount, however your hood may differ.
Step 2: Materials/ Supplies
LED's - blue in color
Wire - small gauge
Power supply (old transformer)
Heat shrink tubing
Step 3: Dismantle Existing Hood
Pretty self explanatory, just take out the bulb, and undo the screws to remove the white reflector. Don't harm the existing wiring or hardware.
Step 4: Mark and Drill Holes
Next we are going to drill holes in the hood to accommodate the LED diodes and the power wires. For the LED's, start small and work up to a size that works well. When you are done with that, insert the LED's watching that the polarity matches up with your plans.
Step 5: Wire Up the LED's
It's time to wire up the LED's in the configuration that you determined in the beginning. I recommend that you leave a few extra inches of wire. If you're using heat shrink tubing, make sure that it is put on the wire before you solder it. I lost count of how many connections I took apart to put the tubing on. Wire in the resistors but don't solder them permanently until you have tested the hood at night on the tank. I soldered and heat shrunk them and then realized that they were too bright. Shrink the tubing on everything but the resistors.
Step 6: Glue LED's in Place
As the title says, glue the LED's in place and make sure that the LED's are straight and the head is not glue covered.
Step 7: Run Power Wires
Run the transformer wires into the hood through the hole you created and connect them. Make sure that the polarity is correct!
More than one hood:
If you haven't already, solder your power wires according to your wiring diagram you created before you began. Feed them through the hole you drilled in your hood.
Step 8: Reassemble Hood
As the title says, reinstall the entire reflector/bulb holder setup into the case. Replace the screws and reinstall the fluorescent tube. If you have more than one hood, move on to step 9, otherwise move on to step 11.
Step 9: Repeat for Each Hood
If you have a longer tank like a 55g and it has two separate hoods, then you are going to need to repeat steps 3 through 8 for the second side.
Step 10: 2+ Hoods: Wire Up Transformer
Pretty self explanatory. Connect the positive wires together and the negative wires together separately. Wire the corresponding transformer wires with them.
Step 11: Test the Lights
It is finally time to test the lights and see if all your hard work has paid off. Just set the hoods upside down on a table and plug them in. Be prepared to unplug it very quickly if something goes wrong.
If the lights don't come on, it is most likely that the polarities of the transformer are reversed. Switch the wires and try it again. If they still don't come on, then open up the hoods and check all the wires and make sure that they are all connected. Also check to make sure that ALL the LED's are wired up with the correct polarity.
Step 12: Reinstall the Hood(s)
The time has come to put the hood(s) back on the aquarium and try them out. If you are using a timer, bypass it for now. You should not be able to tell that the LED's are on if the main lights are on as well. Turn off all the house and aquarium lights and take a look at your good job.
Step 13: Optional Timer
You don't necessarily need a timer as these use so little power. If you want to you can, just set it to come on 1hr before main lights go out and off 1hr after the lights come on in the morning.
My lights have been on 24/7 for a month now without problems.