I've had my 55 gallon aquarium for half a year and wondered "What do my fish do after the main lights go out?" I searched the internet and came across the idea of using blue twilight to simulate "moon lighting". After digging a closer look and deeper on the aquarium coffe table, I discovered that they were just blue LEDs. Easy enough, I thought. That led me to start designing my own. This instructable focuses on the 'kit' style hoods. If you have a different style, you'll have to find another way to mount the LEDs. Make sure you read through the entire instructable before you begin.
Step 1: planning
Once you have decided to build these lamps, you need to decide how many LEDs to use and which ones. I went with 8 LED's, 4 in each hood and it turned out perfect. Determine which LED you will be using and what your power source will be. I used to have the LEDs were rated for 2.8V my power source was an old wall wart that was rated for 6VDC be sure to really check out the voltage that was rated up to 9.9V from the supply like me! Don't forget that when you work with LEDs, you need to limit the current using resistors in the circuit. You can do the math, but too lazy, I used this page and it was awesome, just plug in your numbers and it does the rest. Now you need to determine how to mount the LEDs. I just drill holes for the LEDs to mount in the existing fluorescent, but your hood may differ.
Step 2: materials / supplies
LED color blue Resistances Wire - small measuring device Power supply (old transformer) screwdriver Gun / soldering iron Lot Glue gun Glue sticks drill Drill bits Optional: Heat shrink tubing Heat gun Helping Hands timer
Step 3: dismantling the existing hood
Pretty self explanatory, just take out the lamp and loosen the screws to remove the white reflector. Do not damage the existing wiring or hardware.
Step 4: mark and drill holes
Next we are going to drill holes in the hood to make room for the LED diodes and the power cables. For the LED's, start smaller and work up to a size that works well. When you are done with that, place the LEDs observing that the polarity matches with your plans.
Step 5: wire the LED
It's time to wire up the LEDs in the configuration you determined in the beginning. I recommend that you leave a few extra inches of wire. If you are using heat shrink tubing, be sure to put it on the wire before soldering it. I stopped counting how many connections I took apart to tighten the hose. Wire into the resistors but don't solder them permanently until you've tested the hood on the tank that night. I soldered and heat shrunk them and then realized they were too bright. Heat shrink tubing on everything but the resistors.
Step 6: glue the LED in place
As the title suggests, glue the LEDs in place and make sure the LEDs are straight and the head is not covered with glue.
Step 7: run power cables
A hood Run the transformer cables into the hood through the hole you created and connect them. Make sure the polarity is correct! More than a hood: If you haven't already, solder your power wires according to your schematic created before you started. Feed them through the hole you drilled in your hood.
Step 8: assembling hood
As the title suggests, install the entire reflector / lamp holder setup into the housing. Put the screws and install the fluorescent tube. If you have more than one hood, go to step 9, otherwise go to step 11.
Step 9: repeat for each hood
If you have a longer tank like a 55g and it has two separate hoods, you're going to have to repeat steps 3 through 8 for the second side.