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  1. #1

    Lightbulb DIY Moon Lights - A Guide

    0 Not allowed!
    This is how I made my moonlights for my 4 foot tank using 8 Super Bright LEDs. I will be going through the steps for my particular LEDs and tank size. If yours differ then try to work it out and email me if you are still having issues.

    Equipment and Supplies:
    Soldering Iron

    12v Wall Wort - A.K.A. Power Pack (anything over 100mA will work fine)
    8 Blue Super Bright LEDs
    2 x 1ohm 1/8 Watt Resistors
    Thin Wire (speaker wire works well)
    Electrical Tape

    Step 1: Planning the Array
    The first step in this project is to work out the array configuration that you require for the LEDs that you have obtained. When you buy your LEDs there are two main things that you need to know about the LEDs that you are buying. You need to know the LED Voltage Drop (or Forward Voltage) and the LED Current Rating in mA. If you donít know the stats for your LEDs then my schematic is a fairly standard one to use so you should be ok.

    I used the online LED Calculator at to help me to create my LED array. This is the specifications that I used for my LEDs:

    If you are using different LEDs, or a different amount of LEDs, then just enter your information and let it work it all out for you.

    The schematic for my LEDs works out like this:

    This calculator also works out the Resistors that are required for this project too. In my case we need 2 x 1 ohm, 1/8 Watt resistors.

    Step 2: Calculating Spacing and Wire Lengths
    So here we have the math section of the tutorial. We need to work out the spacing required for your hood and tank length.

    My moon lights are for a 120cm (4 foot) tank and hood. To space 8 LEDs evenly on this tank I need to have them placed every 13.3cm (5-1/4in). Because the array above uses two circuits it is probably easiest to have each circuit staggered alternately (E.G. have an LED from one circuit followed by one from the other circuit). To do this we need to double the spacing to get out wire lengths. So for my moon lights I needed 6 pieces of wire cut to 26.6cm (10-1/2in).

    Step 3: Tinning
    If you have never soldered before, now would be a really good place to stop and search Google for some tips.

    Tinning is the process of adding a small amount of solder to the bare ends of the pieces you want to solder together so that the two bits of solder melt together to get a better joint than you would get by trying to add solder later.

    Strip all the ends of the wires and tin them.

    Now that that is done, grab your LEDs. You need to trim the legs on these to about 3mm (1/8in). These can then be tinned as well.

    Grab two resistors out of their bag and trim both ends of each to 3mm (1/8in) and then tin them too.

    Step 4: Soldering the Arrays
    LEDs are polarity sensitive, meaning that they can only light up if they are given power to the correct leg of the LED. It also means that if you get one wrong in your circuit, the whole circuit wonít work as the power wonít be getting to the ground wire.

    There are a few ways to tell the polarity of an LED. You can look at the Ďflagsí inside the plastic bit of the LED. The small flag is the positive leg, the large flag is the negative leg. There should also be a notch out of one side of the plastic, the side with the notch is the negative side. The last way is that the positive leg is longer than the negative, but you have cut them both off so this way wonít help you this time.

    Grab one of your wires, an LED, your soldering iron and some pliers. Find the negative leg on the LED (the big flag). We need to hold the wire and the negative leg of the LED together while heating the solder that you used to tin each of these. It should melt and fuse the two items together.
    Please use the pliers as it gets extremely hot. Solder only melts after it reaches 186įC (368įF).

    Once you have done your first joint, get another LED and find the positive leg (the small flag) and solder this to the other end of your fist wire. Solder another piece of wire to the negative on this LED. Continue this negative to positive series until you have connected your fourth LEDís positive leg to the end of the third piece of wire.

    The negative leg of the fourth LED needs to have one of your resistors connected to it. Grab one of the ones that you tinned earlier and connect either end of it to the negative of your last LED in your string.

    Thatís one circuit completed. Now go and do the same thing again for your second string of LEDs. Iíll wait here.

    Step 5: Grounding
    So now we have two strings of LEDs. On one end of each string you should have a tinned positive lead and on the other end you should have a tinned resistor leg. Good.

    We need to connect one of the resistors to another piece of wire which we will use as the ground wire. Grab a long piece of wire; it needs to be about 120cm (4 foot) long as it needs to reach the start of your strings when completed. Strip one end and tin it. Connect one of the resistors to the tinned end of this wire.

    We now need to space the two strings of LEDs correctly so that the second ground connection can be made in the correct place. Basically, grab the string that isnít connected to the ground wire and measure 13.3cm (5-1/4in) from the first LED in this string. Place the first LED from the second string in the spot that we measured. Temporarily tape them together in place.


  2. #2


    0 Not allowed!
    Continue taping down the length of the two strings, taping each LED to the other wire so as to keep them spaced correctly. When you get to the first resistor (it should be the one without the ground wire attached) you will need to strip a bit of the plastic from the ground wire to connect it to the resistor. The easiest way to do this for mid-wire connections like this (and the soldering purists out there will be cringing) is to take your soldering iron and melt the plastic away from the wire inside. Do this at the exact place that the resistor leg meets the ground wire. Solder the resistor leg to this bit of clear wire. This is probably the hardest join you have to make in this project.

    Thatís the grounding completed.

    Step 6: Testing
    Itís a good idea to check your connections with a multimeter at this point to make sure they are all good. Turn your multimeter on to itís resistance/continuity setting. You want to make sure that power is flowing all the way from the leg of your first LEDs in each string, back to the end of the ground wire.

    Place your positive multimeter lead on the first LEDs positive leg and the negative lead on the end of the ground wire. It should show a number on the screen, or zero. It should not say OL. If it does then there is a problem with one of your connections or an LED is around the wrong way somewhere in that string. Try the other string too in the same way.

    If all is good, continue on. If you get an OL response, check all your connections and donít proceed to the next step until you fix the problem as it wonít work anyway.

    Step 7: Power Connections
    This is where we need to get out the wall wort (power pack) and cut off whatever end is on it. We need the wires, not any sockets that it might come with. Strip the ends of both wires, obviously one will be positive and one will be negative. To work out which is which you should use a multimeter. Turn it on to itís DC setting. Spread the two wires on the wall wort away from each other so they cannot touch each other. Plug it in to a wall socket and place the probes from your multimeter on each wire. When you get a reading, probably somewhere in the range of 14v, it will either read as a positive or negative figure. If it is positive, the red lead from your multimeter is on the positive wire, if it is a negative figure then itís on the negative wire. Make a note of which is which, tape one of them if it helps you to remember.

    Disconnect your wall wort and take it back to your work station. We need to get the two tinned positive LED legs to connect to the positive wire from the wall wort. I found the easiest method to do this was to solder another wire from the second LED on your now completed string of 8 LEDs (the first LED in the second string) so that you have the required length to solder it, and the first led, to the positive lead of the wall wort. Trim the ground wire to the same length as the other wires and solder it to the negative wire on the wall wort.

    Step 8: Tidy Up
    This is where we can remove the temporary tape and tape everything up nicely. You want to tape all the joints first to make sure there are no shorts at any stage. Once this is done properly, you can tape up all the wires and make it look pretty.

    This is the results that I get with mine. Excuse the empty tank, still getting it set up.

  3. #3

    Join Date
    Apr 2008
    Brisbane Australia

    Awards Showcase

    Here is a cuter version for you. - smaug a cory for your latest sucess :) - graceluvsplatys Great new tank,! Hope it brings you lots of M.T.S lol - Ryuu Yay I got my first two awards! - Gemini No Message - Wild Turkey 
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    0 Not allowed!
    Wow! Thanks for the detailed write up Taz!
    Fish are friends, not an expendable entertainment device!

  4. #4


    0 Not allowed!
    Your Welcome. Hopefully someone finds it useful and takes the plunge. It really isn't that hard to do.

  5. #5


    0 Not allowed!
    What kind of brightness out of the lcds you used? I think I have a bunch from my old modding days, think they are between 7k to 10k mcd.

    Good tutorial. Only thing I can think of to suggest is heat shrink tubing over the joints instead of tape.

  6. #6


    0 Not allowed!
    Quote Originally Posted by korith
    What kind of brightness out of the lcds you used? I think I have a bunch from my old modding days, think they are between 7k to 10k mcd.
    I don't remember what brightness they are. Mine were from my old modding days too... LOL. Used them in my XBOX and in my car. I think they may have been 8000k. But really not sure. Picked up a pack of 50 on eBay years ago.

    Quote Originally Posted by korith
    Good tutorial. Only thing I can think of to suggest is heat shrink tubing over the joints instead of tape.
    I would have used heat shrink but didn't have any on hand. Would be a good addition though. Thanks for the heads up.

  7. #7


    0 Not allowed!
    Quote Originally Posted by TazManiac
    I don't remember what brightness they are. Mine were from my old modding days too... LOL. Used them in my XBOX and in my car. I think they may have been 8000k. But really not sure. Picked up a pack of 50 on eBay years ago.
    Same here got a bunch of them left from then too, I used to mod those for people. Make lcd rings and custom xbox logo.

    I wonder if you could put the leds and wiring into a large hose or other tubing, to soften the light a bit to avoid spotlight effect. Spotlight is ok too could point them onto decorations in the tank, driftwood, rocks, that sort of thing. Think I'll give it a try sometime.

  8. #8


    0 Not allowed!
    You could definitely poke it into some tubing. Never thought of that. I have some here from my Home Brew setup so might get a shot of it tonight with it inside the tubing if I can be bothered un-taping it.

  9. #9


    0 Not allowed!
    Very cool look and well written tutorial. Nice job!
    8 tanks running now:
    1x 220 gallon, 2x55 gallon, 1x40 gallon long, 1x29 gallon, 1x20 gallon long, 1x5.5 gallon, 1x2 gallon
    Gouramis, barbs, rasboras, plecos, corys, tetras, fancy guppies, swordtails, ottos, rainbow shark, upside-down catfish, snails, and Max and Sparkles the bettas.

  10. Default

    0 Not allowed!
    That LED calculator seems a bit wonky to me. That one ohm resistor is going to cause you problems.

    Lets look at it this way. If you have power supply variations, if your wall wart is 13V instead of 12V, then you are going to have (13-4x3)/1 = 1 Amp of current through your LEDs. Most power supplies are not that tightly regulated. Your design is exquisitely sensitive to input voltage which is not a good thing.

    You could do 1 of 2 things.

    1. Increase the input voltage and resistance. If you use 16V, you'd need a 200 ohm 1/2W resistor.

    2. go with 3 strings of 3 LEDs (instead of 2 strings of 4). You'd need a 150 ohm 1/2W resistor for each string.

    This has the advantage of desensitizing & stabilizing the light output to voltage variations and saving your LEDs. Using the #1 design, if your input voltage rose by 1V, you change from .02A of current to just .025A. Your design goes from .02A to 1A.

    I would stop using that LED calculator. Seriously.

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