We present a physically-based method for animating and rendering lightning and other electric arcs. For the simulation, we present the dielectric breakdown model, an elegant formulation of electrical pattern formation. We then extend the model to animate a sustained, "dancing" electrical arc, by using a simplified Helmholtz equation for propagating electromagnetic waves. For rendering, we use a convolution kernel to produce results competitive with Monte Carlo ray tracing. Lastly, we present user parameters for manipulation of the simulation patterns.