As seen in the New York Times article "Dinner is Printed' by AJ Jacobs. Flame part of three-part 3D-printed Candle (full candle requires top, bottom, and flame). This three-piece plastic candle fits perfectly with the Candle Holder and Cap. You never have to worry about setting things on fire or dripping wax, all you need is an LED to make this design flicker and glow.
For light-up and flickering effect you will need one of these LEDs: http://www.lilyleds.com/Products/133/Flickering-Candle-LEDs and a coin-cell battery. Transparent detail is recommended so the LED can shine through.