Here’s a great example of how you can make a simulated LED flame using Arduino and some LEDs. If you are looking for that special flame effect for this Halloween without all the really hazardous fire, this might be a great alternative to real fire.
The code accepts an arbitrary number of LED outputs, with a minimum brightness for the general glow. A peak brightness and traversal time are generated randomly, and the timed traversal smoothly walks across the outputs. The peak falls off, so the effect is of a smooth motion of the peak across the LEDs, to an arbitrary position along the line of outputs (as a float, rather than always peaking at a specific light). When arranged in a circle, it feels like the light is moving around the group, which casts moving shadows, and gives a flickering effect that’s much more convincing that a single light variably changing brightness.