Step 1: Materials Needed:
1. Santa or Elf hats from local store of choice. The thicker pile ones work better as they hide the slit you cut for the LED better. You can get them for $3-$7 at your local drug store. The thicker pile are a couple bucks more. The elf hats have a thick felt that works well too.
2. Battery powered string of LED lights. I got mine from Walgreens. They are $4, or they are on sale all the time for 3/$10. The ones I purchased last year had 20, 2mm clear, LED's. They are very bright and add a nice sparkle. They were powered by 4 AA's and will run continuously for days. The ones for sale this year have 15, water color, 5mm, LED's, powered by 2 AA's. They will run for about 4 days on one set of batteries. The 2 AA's is nice because it makes the hat lighter and also makes it easier to hide the battery pack.
Do NOT use regular battery powered Christmas light bulbs! They are incandescent bulbs that will get hot, and can burn you or the fabric. They will also eat batteries like crazy. Only use LED strings.
3. Hot glue gun and glue sticks
4. Small sharp pen knife.
5. Clean work surface you won't mind getting some hot glue on.
Step 2: Prep Work...
You should have your work space, a string or 2 of lights, a hat, your pen knife, and your glue gun plugged in and getting warm.
Take your hat and turn it inside out. All the work and wiring goes inside the hat, so it is way easier if you just turn it inside out now. On some hats the white ruff is sewn to the red so that you can't invert it easily. Just use some small scissors or the pen knife to undo the seam. It is usally just a couple stiches, if any, in the back along the seam.
In the hat on this page, I will use 2 strings, but more on that later. Just look at the white ruff for now.
The hat will lay flat on the table effectively giving you 2 sides, front and back. Take the total number of lights on the string and divide by 2. 1/2 on the front and 1/2 on the back. Be sure to fold the ruff up as shown so you know how low you can go on the red part of the hat. If you do not fold the ruff back up on the red, you could place LED's below where the white ruff lays and hide some of your LEDs.
For my string of 15 lights I placed 7 on the front and 8 on the back. Just place marks randomly on the fabric with a marker. You need to place a couple close to the edges and not clump them all in the middle to much. When you have marked the first side, flip it over and mark the other side now too. This will make gluing the LEDs in place go faster.
The battery case tucks inside the ruff when it is folded up. Or, you can velcro it up into the hat by opening the seam at the back of the hat where the red material meets the white ruff material and sliding the battery case through.
Step 3: Surgery...
So here we get to the meat of it all. Once you have used the marker to lay out where you want to place the lights, take the LED that is closest to the battery pack. Make your first cut the slit that is closest to the seam that runs up the back of the hat. This is so the first LED will be close to the back, and to the bottom of the hat for easier placement of the battery pack into the ruff of the hat. So you will start at the bottom of one side of the hat, work your way up to the top, then flip the hat over and work your way back towards the bottom on the second side. You only want the slit large enough for the LED to fit through. That is why a small pen knife works best. Don't worry if it is a little larger. The hot glue will seal it and keep things in place.
Slide the LED through the slit just far enough so that the lens of the LED is all the way through the slit. Take your hot glue gun and squirt a dab of hot glue on the led and the fabric. Don't worry if the LED moves around, the glue takes a minute to stiffen up, so you can safely put the glue gun down and adjust the LED. Hold it there while it cools for a minute so that it hardens enough to hold the LED in place before you go on to the next one. If you get impatient the LEDs will move out of place. So just take your time and wait for each one to cool enough to firmly hold the LED in place.
Rinse. Lather. Repeat - with each of the remaining LEDs on the string.
If the wires get in the way, just press them flat to the fabric and use some hot glue to tack them in place.
Step 4: Wrap Up...
The first generation hats were 20 LED strings with 4 AA batteries. The LED's were smaller, but they were bright, and the lens was a clear lens so they had a lot of sparkle. They were either all on or all flash. The latest versions have 15 LED's.
I have made a few hats with 2 strands, white in the ruff, and red/green on the top part of the hat. I carefully cut the power leads on one of the strands and soldered back into the battery case of the 2nd strand so I can power both strands from one battery case. This lets me control both sets of lights independently, so I can have the white on, and the red/green flash, or whatever.
For even something even more complicated, I took the power leads of the second string, and added to the first string after the flash circuit. So the second string would only get power when the first string was set to on or flashing. This made the second string have an interesting strobe effect.