Christmas light bulbs are incandescent and burn out at an ever increasing rate. This was fast enough that my roommates and I got blisters from pulling them. I had those lights up for over two years and I wasn't about to go without ambient lighting. I figured LEDs were the way to go.
Each module is powered by 12V and is relatively simple in concept. The number of LEDs you need per module depends on the voltage of the LED. You'll typically be able to get 3 blues or greens (3.4V each) on a module or 5 reds (2.4V each) on a module. A VERY large number of modules can be powered off of one supply. The maximum number of modules that can be powered by a single supply can handle is its amperage divided by the current a single LED pulls. In my case, I used a 12V 5A power supply from Digium and 20mA LEDs, so that gave me 250 (5/0.02) modules per supply. That's a whole lot of light!
Parts for each module:
A piece of breadboard
3 blue LEDs (3.4V)
A 100 ohm resistor
2 small neodymium magnets
2 ferromagnetic thumbtacks
Hot Glue Gun
A 12V Power Supply
Step 1: Materials and Organization
Your first task is to gather your materials and find the module configuration that suits you. For each module, you'll need some perfboard (the really cheap stuff if possible), a 100 ohm resistor, three 3.4V blue LEDs, two 1/8"x1/8" neodymium magnets, and two ferromagnetic thumbtacks. For general supplies, you're going to need a 12V power supply, some cheap speaker wire, a soldering iron, some solder (lead/tin), a hot glue gun, and some glue sticks to go with it. A third hand pcb holder is helpful, but not required. As for organization on the perfboard, it's really up to you, but I chose long and skinny so my modules would have a similar profile to the wire itself and be less obtrusive.
Once you have decided where the LEDs go, make sure that they are in the correct orientation. The longer lead is positive and goes away from the resistor. The resistor will be the link to the ground for the module. I left a gap between the perfboard and the LEDs so that I could bend them and better distribute the light. Bend the leads that are going to connect toward each other so that they lay parallel and almost touch. The end result of this is shown in the next step.