The flame effects on an electric fireplace are most commonly created using a light source with a rotating rod that contains an array of strategically placed mirrors. 

There will be a motor attached to the end of the rod. As the rod rotates, light is reflected off the mirrors onto the front screen of the fireplace.

The mirrors are placed on the rod in such a way that when the light is reflected onto the screen it imitates the look of flickering flames.

We have an electric fireplace stove and the video below shows the flame effects working from inside the fireplace.

For more information on how the flame effects work we have a complete guide to how an electric fireplace works.