It's an ARB_fragment_program, i.e. a little program uploaded to the GPU and run per pixel. I made the first
"prototype" (<< includes screenshots) a while ago to show a sensor problem (and my framerate with -O0 and thousands of sensors

). Later z-man made a headlight and I went thinking "how can I make this look good, and get good performance too?".
The program places a point light 1 distance above the cycle, of brightness speed^2 and the color of its cycle. It does diffuse lighting with quadratic attenuation.