Glow Starter? There's no glow starter as far as I can see. Could be thermal switch (glass tube at base area) which explains the filaments remaining on even after the arc struck.

I actually have a video of a North American 400w M135/M155 pulse start metal halide lamp starting up like a preheat fluorescent lamp using an ignitor with a glow starter:

https://youtu.be/wzdPsR1MPe4

I actually have a video of a North American 400w M135/M155 pulse start metal halide lamp starting up like a preheat fluorescent lamp using an ignitor with a glow starter:

https://youtu.be/wzdPsR1MPe4

But it is no preheat. It just generates the "inductive kick" as an ignition pulse.