The deep sea anglerfish is a bony fish with enormous teeth, best known for its unusual method of catching prey - a worm-like bioluminescent 'lantern' protruding from its forehead is wiggled about to entice smaller fish to come near for a closer look - and an untimely demise. Here is an easy way to construct an eerie luminescent growth to make your own spooky anglerfish jack o' lantern.
The supplies should cost about $10 or less. You will need:
1x pumpkin (of course!)
1x Blue LED
Stiff wire (coat hanger, florist's wire, etc.) to maintain the growth's shape
Electrical wire (insulated or enameled) - at least a couple feet. Thinner wire will be easier to hide.
Battery holder (4x "AA" or "AAA" (etc.), or 9V battery snap) and batteries
Resistor (value depends on battery holder)
Hot-melt glue and gluegun
Step 1: Choose Your Battery Holder and Resistor
The first step is to pick a battery holder, then a resistor (or vice versa, depending on availability). The most common battery holders that will work for this project are either a 4x 1.5V cell holder (that is, four AAA, AA, C, or D cells in series), or a single 9V battery holder. The blue LED requires only a small amount of power; without a resistor to slow down the current flow from the batteries, it will burn out very soon!
A resistor's "stopping power" or resistance is measured in Ohms; the higher this value, the more strongly it resists the flow of current. A typical blue LED can handle 20-30mA of current. For either type of battery holder, a resistor value in the range of 250 to 560 will work fine (you can use higher values to make the LED dimmer). If you are using a 4-cell holder, you can go as low as 100 ohms.
1/4 Watt is the most common size of resistor you will find, and will be fine for this project. You can use larger wattages (1/2W, etc.) if you have one lying around, but I wouldn't recommend going smaller. Since it's hard to inscribe a numeric value on the round package (and harder still to read!), resistors at this size are normally marked with colored bands to indicate the resistance. If you are faced with a package of assorted resistors without numeric values, look up "resistor color code" for help in identifying the correct one.
Step 2: Building the Lantern Appendage
First, identify the anode (positive) end of the LED. The anode is always the longer of the two leads. An LED will only conduct electricity in one direction; if you wire it up backward, it will just sit there darkly and mock you. Attach a length of wire (at least a couple feet) to each lead, being sure to mark one (or use different colored wires) so you can identify the anode later.
Take about 6 inches of stiff wire (a piece of coat hanger or floral wire work nicely) and bend it into the desired shape of the lantern appendage. This will form the center of the lighted appendage and help it maintain its shape. In a real anglerfish it protrudes from the forehead and dangles tantalizingly over its gaping maw, but arrange it how you like. Squirt a dab of hot glue at the forward end of the stiff wire, then quickly (before the glue hardens) touch the LED to the glue so that it sticks, facing forward. If your stiffener is bare metal, make sure that any exposed wires/metal from the LED do not come in contact with it, in order to prevent a short-circuit.
Lead the wires back toward the rear of the stiffener, tacking them to what will be the underside with a bit of hot glue at intervals. Leave the last couple inches of stiffener free of glue so that it can be easily poked through the jack o'lantern's forehead.
Now that everything is held in place, goop all but the bottom couple inches of the stiffener with hot glue, wires and all. Starting at the LED, run beads of glue over the stiffener toward its base, working your way around until it is completely covered, and as lumpy and organic as desired. You'll want to add a nice thick blob of hot glue around and in front of the LED itself, this will diffuse the light and help it spread down the metal stiffener. Don't worry too much about the wires being visible right now; in the dark, the bright glow from the end will help conceal them.
Step 3: Carve the Pumpkin
I won't go into too much detail here; carve up the pumpkin as desired. The anglerfish has long, sharp, pointy teeth; if your pumpkin does too, make sure to protect them from drying out or the thin parts will quickly shrivel up to nothing in the crisp autumn air. You can see what happened to mine below for carving it a few days early and leaving it to sit around unprotected - the teeth used to be much larger and extended nearly from top to bottom and vice versa.
If possible, save the plug(s) you carve out so they can be placed back in at night to slow this process. Alternatively, rubbing a light coat of olive oil over the thin parts should help keep the moisture in.
Step 4: Wiring and Finishing
Punch the bottom end of the 'lantern' through the pumpkin's forehead to form a hole. This is a good place to thread the wires through to keep them out of view. Punch another hole at the rear of the pumpkin for a wire exit. Thread the wires through the first hole and out the exit hole, then replace the lantern back into its original hole. It may be a snug fit now that it is sharing space with its wires.
Wire the battery holder and resistor to the LED lantern's wires as shown. Remember to be sure the anode (longer lead; positive) you identified earlier is wired to the + side of the battery. If you have wired everything and the LED does not light, try reversing the wires to the LED.