Light bulb is a period-2 oscillator that was found in 1971. Its rotor, known as the filament, is the only known 3-cell period 2 rotor, and it can be embedded in a slightly smaller stator, giving the 21-cell variant shown below. Two other variants of this oscillator are also known. Various other small induction coils can also be used in place of the snake at the top of the bulb, including house and bookend, (the latter of which has a known 6-glider synthesis for the resulting oscillator) though these lead to larger bounding boxes.
The first soup-based syntheses for this oscillator were discovered by Mark Niemiec on December 17, 2004 based on results from Andrzej Okrasinski's census, costing 11 gliders for the house-stabilized version and 16 for the bookend-stabilized version.
A variant of the light bulb that is 2 cells smaller.