This is a simple LEGO project which uses LEDs and a button cell to create the effect of glowing candle. I originally created these back in October 2016 for components of my Halloween LEGO photo display. The design and electrical portion were ultimately created as a result of trial and error, and made to be as simple and minimalist as possible. If followed accordingly, each candle contains 29 LEGO pieces, one LED, one battery, and a few wires. This project requires some soldering, but substitutions can be made where applicable.

Like the rest of my other LEGO projects, you're free to deviate from the design and use your own colors/pieces. In this model, the candle itself is white, with a dark grey candlestick, and a flickering LED. You can do such things as making the candles different colors, re-designing the candlestick, or even omitting the flickering function for a simple standard glowing LED. You could also use this basic tutorial as a mere suggestion for making a completely different candle concept, such as a small round votive candle made from LEGO bricks.

Step 1: Construction of the LEGO Portion

The candle only requires 29 common LEGO pieces, if using my design verbatim. I purchase most of my pieces from BrickLink.com, which is a huge online retailer for individual LEGO pieces from various sellers. Although my photos should be self-explanatory for construction, I've also included a LEGO Digital Designer file of the candle model, in case you'd like to examine it more thoroughly or change the colors/design.

Candle-LEGO.zip
Download

Step 2: Assembling the Electronic Innards

Apart from connecting some components together inside the candles, no other electrical work is required (e.g. Arduino, coding, transistors, et cetera), and the electrical work in this model is rather novice.

Electronic supplies needed:

CR927 3V button cell: these can be found at major retailers like Walmart or Target for about $5 for a pack of five. I think I bought mine from Party City for cheaper, since they were sold alongside illuminated Halloween costume components. Any 3V button cell can be substituted, so long as it's small enough to fit in the bottom of the candlestick holder.
Micro toggle slide switch ($1.49 USD). I bought mine from the Tinkersphere store in New York City, but you can get this specific part from the previous URL. You can probably find similar ones from Radio Shack or eBay. The key is that it has to be a small toggle switch, and not a momentary switch.
Flickering LED: I used 5mm LEDs at the for this model, since they're the only ones I had in my toolkit at the time of production, but 3mm LEDs would be a better fit. If using 5mm LEDs, the sides of the LED bulb must be clipped with scissors or sanded down, so that they can fit within the LEGO pieces. 3mm LEDs fit easily within the LEGO brick for the flame. Flickering LEDs are somewhat difficult to find in stores, so any regular white or yellow LED can suffice, if you want to forego the flickering effect for a standard glow.
26-30 AWG wire, preferably two different colors to distinguish positive from ground connections. I always use red and black wires for building circuits.
Soldering iron
Solder
Electrical tape
Needlenose pliers

Due to the nature of the button cell, no resistors are needed, and they are wired directly to the switch and LED.

Using wire cutters, cut a ~9.5cm (7.67 inches) strip of black wire and strip both ends.
Cut two strips of red wire: ~16.5cm (6.49 inches) and ~3cm (1.18 inches), and strip both ends of both pieces.
Solder the red wire to the anode (long leg) of the LED.
Solder the longer black wire to the cathode (short leg) of the LED.
Tape a small strip of electrical tape around either the anode or cathode solder connection: this is done strictly to prevent the anode and cathode from making contact. If both wires connect while the candle is powered, it'll create a short circuit. Also adding a small strip of tape around the connection will help keep the wires inside the candle tube.
Place the transparent orange LEGO "flame" piece over top of the LED.
Slide the two long wires down the inside of the white candle tube (consisting of 14 round white bricks).
With the red and black wires hanging out of the end of the white candle tube, attach the candle to the candlestick. The black wire should go all of the way through the grey candlestick holder and coming out from the end.
The red wire should poke through the small gap in the four 1x1 round bricks. The 4th brick -- a 1x1 cone -- is there since it creates a gap for the smaller red wire to poke through. You can disassemble parts of the candlestick base to allow the red wire to come through the tiny clearance, and then rebuild the base around the wires.
Slide the smaller red wire through the bottom gap of the 1x1 round bricks, and allow it to come out through the bottom of the candlestick. As with the step above, you can disassemble pieces of the base and rebuild the base around the wires.
The black wire and the small red wire should be flush without about half an inch of slack coming out of the bottom of the candlestick holder.
If using the same slide switch as I purchased, clip off one of the left or right pins, so that only two pins come from the switch. Solder one pin to the 1st red wire and the other pin to the 2nd red wire.
Carefully tape the button cell to the wires at the bottom, making sure to have proper polarity. The top of the battery -- the smooth side with the text -- is the positive (+) connection, and the bottom side with the textured surface is the negative/ground (-) connection. I usually start by laying out a small strip of electrical tape, then I place the black wire stripped end to the tape flat. I placed the bottom of the battery over the top of stripped wire, then I placed the stripped red wire over top of the battery. Carefully I wrapped the tape around the battery and two wire connections. NOTE: I had trouble keeping the stripped wired ends taped to the battery, so I soldered two small metal pieces at the ends of the wires. The metal strips were clipped off male wire spade connectors.
Flick the switch to test the connection. If the LED does not glow, it means you have a faulty connection, a dead battery, or most likely the battery wrapping wasn't done tightly. With the switch still on, squeeze down on the wrapped battery to see if any light comes from the top of the candle. If the LED glows brightly as you squeeze down on the wrapped battery, it means you need to wrap it tighter. Sometimes this tightness issue gets resolved when you cram the wrapped battery into the bottom chamber of the candlestick base.
If functioning properly, carefully attach the bottom to the candlestick holder.

Step 3: Fire Fire FIRE!!!

With any luck, your candle should be glowing and flickering like a champ. As mentioned in the previous step, here are some troubleshooting methods to try if the light won't go on, or if the LED is too dim:

Before connecting all of the electronic parts together, test out the LED, switch, and battery individually on a breadboard or with a voltmeter to see if they're functioning.
When taping the battery to the wires, make sure it's wrapped tightly, and that the red and black wires don't touch each other. The red wire should touch only the top (shiny part) of the battery, and the black wire should only touch the bottom (textured part) of the battery. If the electrical tape wrapping isn't tight enough, the connections will come loose. Sometimes if the connections are loose, this can be resolved by cramming the wrapped battery inside the bottom of the candlestick holder, which securely keeps the whole wrap in place.
Make sure the proper polarity is used for the LED: red wire to anode (long pin) and black wire to cathode (shorter pin). The anode and cathode should never touch, as this creates a short circuit -- hence why I recommend wrapping a small piece of tape around either one of the LED's pins after soldering.

-Baron von Brunk

Credits: photography and video recording by Julius von Brunk