It's actually kind of amazing the activity that happens at night, especially if you have a saltwater tank with lots of invertebrates and corals!
Here I have documented the steps necessary to create a simple, low-cost moonlight that you can place above your aquarium to simulate the natural moonlight that fish would experience in the wild. This will also give yourself, the caretaker more nocturnal viewing options.
Note: I'll add in some pictures of it on my tank when I get home tomorrow!
Step 1: Gather Materials
1 T-8 fluorescent tube holder (available by the fluorescent fixtures for $3 at Home Depot)
1 piece of 8x10 1/8 inch acrylic ($2 at home depot)
2 White 5mm LEDs (radioshack #276-0017 for $2. They are 7000mcd intensity, 30 degree, 3.3volt 25milliamp)
2 UV 5mm LEDs (rs #276-0014 for $2. They are 280mcd, 30 degree, 3.2v 20ma)
1 rectangular blue LED (rs#276-0013 for $2. They are 350 mcd, 154 degree, 3.2v 20ma)
1 pack of 47 ohm, 1/2 watt resistors, $1 at radioshack
1 pack of 39 ohm, 1/2 watt resistors, $1 at radioshack (Optional)
1 pack of LED holders $1.50 at radioshack
1 length of extra T-5 networking cable or phone cable
1 extra power adapter. Mine happened to be an old Samsung cell phone charger, model TAD037JBE. It takes my 110volt AC and changes it to 5v DC @ .7a.
1 Styrofoam plate
So total, I spent about $15 in materials, assuming you have some small gauge wires around your house and an old power adapter.
Remember that unless you have a 5volt power adapter you must change the resistors out... for example, if all you can find is a 9 volt power adapter, that will work, but you will have to buy resistors with higher ratings or else you will overpower your LED's and they'll burn out. If you need to re-calculate your resistance, use a web calculator like this one: LED Calculator
Tools you might want:
Hot glue gun
Step 2: Schematics
You'll notice that I hooked these up in parallel. I did this because my power adapter only has a 5v output. By running the LEDs in parallel each LED gets up to 5v. The other option is to hook them up in a series, but then I would need a power source capable of providing enough current for each LED individually (say I have 5 LEDs that each require 3 v I would need a power adapter with an output of 15v).
On a side note, since I couldn't find 39 ohm resistors I just used the 47 ohm resistors for each LED.
Step 3: Assembly
1) Cut your acrylic into strips just as wide as the inside diameter of the light tube. I think mine was 1 3/16" I cut 3 8" strips since I wanted a 24" light.
2) Drill out 1/4 inch holes in the acrylic spaced out how you would like.
3) Insert the LED holders into the holes and then mount the LEDs. You might need to ream out the holes a little with the end of a file if they don't quite fit. I then used hot glue to hold the LEDs there.
4) Locate the longer of the 2 prongs on the back of the LEDs. The longer of the 2 is the positive (+) contact, mark that with a permanent marker or something.
5) bend the contacts flat on a diagonal and so that all the (+) and (-) contacts are on the same side.
6) Solder all of your negative contacts together. Use some extra wire between the LEDs so you can move the acrylic slides within the tube.
7) solder resistors onto your positive contacts, or solder them together and put a resistor on the end that you will be attaching power to. Leave extra wire.
8) I used the sheath of the network cable run along the (+) side to ensure that the contacts don't short, but you can use e-tape, wire nuts, or whatever you want. Just be sure they don't touch. This would be a good time to go ahead and test it. Temporarily wire in the power adapter and plug it in.
9) To seal the end-caps I used a Styrofoam plate. I pressed the endcap into the plate and cut out the circle it made. Then I used hot glue to seal them completely and center the cord from the power adapter. (see pic)
10) Slide all the acrylic plates into the tube and put on the end-caps and you're done!