Engineering at Home: Make Your Own Lightbulb

Step #1: Hollow-Out Your Screws

To hollow out your screws, drill a 3/32" hole through the middle of each one. Two of these hollowed-out screws will be turned into vents for filling the jar with CO2. The other two are for holding the wire hangers.

When drilling, you’ll find it’s much easier if you drill a hole in a piece of wood to hold the screw in place while you hollow it out. 

There is a chance you may mess up a screw or two, so it’s a good idea to purchase extra screws to be sure you still have enough to finish the project without having to go back to the store to buy more.

Step #2: Get Your Lid Ready

To get your lid ready, use a marker to make dots where you want the holes to go. You should have four holes in total that are equally spaced apart.

Use a drill to make the holes, then grab a penknife to score the area around each hole on each side of the lid. You’ll be using epoxy in these holes later, and this allows it to adhere better.

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Step #3: Prepare and Insulate the Hangers

Cut two pieces of malleable wire, about 10" long. Clamp the wire with vise grips leaving about 1.5" of extra wire sticking out on one side. Then, hold the piano wire against the vise grips, so it appears perpendicular to the wire. Using your needle-nosed pliers, twist the wire around the piano wire.

Repeat the steps above to make the second hanger.

Note: For malleable wire, you may use 19 gauge stainless steel, but any solid core wire of a similar gauge should work.

Let go of the vise-grips and remove the piano wire. You should now have an excellent coil to hold the filament. Place a piece of mechanical pencil lead inside the coil. It will be very loose. 

Gently adjust the coil with the needle-nosed pliers so that it tightly holds the pencil lead in place. Make small adjustments only to prevent breaking the lead, and then cut the extra length of wire off the coil.

Repeat the steps above for the second wire and then bend the two wires, so it holds the pencil lead vertically and center, so the long leads align with the lid holes. 

Cut a 1" length of heat-shrink tubing. Place it around the wire hanger at the spot where it goes through the lid, about 4.5" from the underside of the longer lead. Apply heat to shrink and adhere to the tubing onto the hanger. A candle is probably the easiest way to apply heat through a lighter, but matches will work as well.

Repeat the steps above for the second hanger.

Step #4: Attach the Screws

Mix a minute amount of JB Weld and apply it to the outside of the heat-shrink tubing.

With the head face down, carefully slide the screw over the tubing and JB Weld. 

The epoxy should completely fill the hole in the screw because you need an airtight seal. Make sure the screw is straight on the wire hanger.

Repeat the steps above for the second hanger.

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Step #5: Mount the Lid and Make the Final Adjustments

Mix a minute amount of JB Weld and apply it to the bottom of the screw head. Push the screw into the hole in the lid with the head face down in the jar. Tighten the nut on the lid's opposite side. Make sure the epoxy fills all gaps to make it airtight.

Repeat for both vent-screws and hanger-screws.

Let the epoxy fully harden for a few hours. To check for a good seal, tighten the lid on the jar, blow into one of your vents while holding your finger over the other one at the same time.

Once the JB Weld has hardened, put your piece of pencil lead in the hangers to see if they fit, and make final adjustments to the hangers' positions. Remove the pencil lead and wash thoroughly (with detergent). Dry the hangers, the bottom of the lid, and inside the jar. The inside of your bulb must be free of any contaminants that might burn and cause discoloration.

Use latex gloves if you have them, for the final assembly. If you don't use gloves, make sure you wash your hands thoroughly as well. Carefully place a new, fresh piece of lead in the hangers. Try not to handle it more than you have to. Tightly screw the lid onto the jar.

Note: You can use 0.7mm lead, though 0.5mm and even 0.3mm should also work. The thinner lead has a higher resistance and should make a brighter bulb.

Step #6: Charge and Test Your Lightbulb

Place the assembled jar in the oven at 180 degrees. It only needs a few minutes to heat. While the jar is heating, apply a minute amount of silicone inside both of your acorn nuts.

You need to do the next step quickly, so you might want to practice it.

Take the jar out of the oven and place it on the table. Use the air nozzle to put CO2 into the jar through one of the vents. Do this for about a minute. The cold CO2 should fill the jar and force the hot oxygen-containing air out of the second vent. 

While continuing to put CO2 into the jar, screw an acorn nut onto the open vent. Remove the air nozzle from the vent, then quickly screw an acorn nut onto it. Tighten both acorn nuts to make a good seal.

Filling this requires an unusual tool, the air nozzle. It is supposed to be an air duster, but regular canister air dusters will not work. They tend to be filled with flammable gases, such as propane. Using one will create a bomb, not a light bulb.

As an alternative to a CO2 canister,  you can use dry ice. Without heating the jar beforehand, place a small piece of dry ice in the jar and let it turn into CO2, displacing the air. After the dry ice has completely disappeared, close and seal the vents, but do not seal the jar with dry ice still inside. It will continue to dissolve and create positive pressure that could become a safety hazard. 

When you first turn the bulb on, it will smoke a bit as the remaining small amount of oxygen in the jar burns. Burn it for about 30 seconds, then let it cool, and the smoke settle.

12 - 24V should be just right for powering the lightbulb, as long as it can provide a high current amount. You can use two 6V NiMH batteries to connect in series.

You can use a multimeter to measure the resistance of the bulb. With the V=IR, find out how much current your bulb will pull. 

As the graphite heats, its resistance decreases. The resistance you measure before turning on the bulb will be higher than when it is on. This is one reason tungsten filaments are used — tungsten's resistance increases with temperature.

Congratulations! Your bulb is now completed!

If you are running your bulb with batteries, make sure you do not overheat your batteries.

It won't be very bright, so don't plan on replacing your household lighting with it. This bulb was merely an experiment to learn how one works, but if you want to increase the brightness, try increasing the voltage with a stronger battery. Just be careful since the higher the voltage, the higher the current.