If anyone has seen the gauges inside a Pontiac G6 (ahem my current car =P, google pics of this light up at night) They have the afterburner effect on those. I have buddy that studied electrical engineering at my university (not claiming him as an expert by any means but he brings up valid points) and after showing him the concept pics he says:
"Here is the key to that look:
The inner circle of the lighting fixture needs to be blacked out or tinted so little (but enough to be legal) light passes through. This will give the darkened center appearance.
The light needs to come from behind this blacked out center in a way that it shines around the perimeter of the light fixture. But some light needs to pass through the darmened center as well but much less than what comes out the sides. This can be done by using a smaller halo light with a softer (no brakes applied) glow. The smaller halo should be fixed behind the darkened center so you cant "see" the halo directly but only the glow it emits.
The sides of the lighting fixture needs to be highly reflective so the light can gleam off it forming streak patterns that mimic a soft glowing flame.
Also the darkened center should have notches cut out along the egdes where light shines through. This allows the light passing through them to have a broken up edge/definition to enhance the soft glowing flame look."
Basically what I got from this and the drawings, you lighting experts can debate this, is the middle of the lamp needs to be tinted or blacked out enough so barely any light comes out when the brake are not
applied. The afterburner effect comes from having the light source be behind this tinted middle so the light shines from behind it onto the sides.
Heres some drawing he did that I photo'd on the iPhone: