Cold Cathodes, or Cold Cathode Fluorescent Lights (CCFLs) are very similar to a normal fluorescent tube used in lighting many offices and signs. These are different in that they do not require a large, high-voltage ballast, but they rather run "cold", with small inverters that amplify voltage to activate a paint coating inside of the tube. CCFLs are simple, cheap, and incredibly bright for their size. They have a tendency to make the air around them glow, which can be very beautiful and even entrancing.
This is perhaps the simplest instructable I have yet made. Parts are minimal, and putting everything together doesn't venture into complex wiring. For all the parts needed to complete three bars, I paid about $80. Using PVC parts, acrylic tubes, CCFLs, and a laptop power supply, we can create some superb lights.
Step 1: Supplies
A cheapy 15W iron from Radioshack.
0.022" Silver Rosin Core Solder ($4)
Becomes molten metal to make electrical connections. Silver helps it heat more easily and flow better, while rosin flux cleans your joints.
Heat-Shrink Tubing ($5-15)
A fair amount of heat-shrinking will be needed in shortening the CCFL wires. eBay has a ton of it for dirt cheap.
Hot-Glue Gun and Glue-Sticks ($5-20)
These will attach the caps to the acrylic pipe, as well as the 9v connectors.
9v Snap Connector ($1.50 each)
Connector available at Radioshack, intended for 9v batteries, we will use them as our "plug".
Electrical Tape ($4)
This tape goes on the underside of the exposed inverter, it prevents electrical shorts.
20 Gauge Speaker Wire - 25 feet ($3-10)
This will provide our extended power wires.
Laptop Power Supplies (~$13 each): They are cheap, regulated (which is normally very expensive), almost always provide 12v+, and are compact. It doesn't matter what brand you buy, we are cutting off the connector for raw wire. Be aware that on eBay some prices are very high, since laptop users whose power brick broke are desperate for a very specific model that matches their computer, it's o.k. to get off-label. Your voltage can be anywhere from 12v->16v. The inverters can take a range of power, pretty much anything under 16v and higher than 10v is acceptable. As far as the power supply rating, 60 Watts is pretty common, and should be plenty for four tubes (I have been running twelve CCFLs inside three tubes from a 64W for a couple months, though it gets very hot). The average single 12 inch CCFL pushes 12v DC @ 400mAh, or around 4.8 Watts per CCFL. To calculate Wattage, simply multiply Volts times Amps.
I prefer getting Fujitsu laptop power supplies, simply because they are compact and they've served me well in the past. Another very acceptable supply are those for large LCD computer monitors (21"+). I just searched "laptop fujitsu 16v 4A" on eBay and bought a supply for $13 including shipping.
Cold Cathode Fluorescent Lights ($6 per 2x 12" Tube Kit)
You have many options here. CCFLs come in various sizes, ranging from 4" -> 36". The largest commonly available colored CCFL is 20", and those generally run about $15-20 per CCFL, and require their own special inverter. For the purposes of this guide, I will be using the most common CCFL type: 12" colored bars. The most common colors are Red, Green, Blue, White, and UV, and I don't suggest unusual colors like Yellow, Orange, or Purple, as they never shine the colors that website photos suggest.
There is a difference between purchasing CCFLs and a CCFL kit. A kit contain two tubes, an inverter, power cords, and a switch, and are generally the best purchase when getting new lights, while just CCFLs means only replacement tubes.
Here are some stores for purchasing CCFLs that I recommend:
MountainMods.com: My favorite place to buy CCFLs, they are a computer website with excellent prices and selection.
Xoxide.com: I'm only listing them because they sell 20" CCFLs which can be hard to find, then again, each costs $20, which can be too expensive, especially when you can get four 12" tubes (48" worth of light) for $12 elsewhere.
FrozenCPU.com: They have the biggest selection of CCFLs I've ever found. They have some very unusual tubes, such as tubes with micro-inverters built into them, focused direction tubes, along with uncommon sizes.
3x Acrylic Pipes -- 57" long, 1 1/4" wide, 1/8" thick (~$12 per pipe)
Whenever I need high quality plastics, I always purchase from TAP Plastics (Plastic Rods on the Left). They sell a huge range of acrylic and polycarbonate materials, though for this guide, we are only using round acrylic tubes.
1 1/4" diameter, 6' long, 1/8" wall pipes are $11.65 each. Watch out for shipping though, I had my pipes cut to 57 inches for some working room and to avoid a $10 oversize shipping charge for anything 6' or longer, cuts are free.
We need a very specific diameter of acrylic, since we want our CCFLs to fit snugly. The widest point of a CCFL (diagonally) is 0.8". CCFLs including their end-cubes are 12.25" long. Subtracting the wall thickness is 1 1/4" - 1/8" = 1.125". This gives our CCFL 0.325" to fit in with, which is perfect since we need some space for wiring. Also take into account the size of the CCFL inverters (shown later), though for me they fit snugly within this 1 1/4" pipe.
To properly adjust the length of the Acrylic pipe.
PVC Ends ~$8-10
6x Caps: These go onto the ends of the Acrylic pipe.
6x Plugs: Though I used caps which go over the PVC pipe which I find easier, you could just as easily use a PVC plug that goes into the pipe to make it more clean/compact. You will need some extra length on your acrylic pipe to make up the difference however.