Red ring impact effect

In various levels, there are Halo control panels that activate things such as bridges, lifts, and doors. If you shoot at one with an assault rifle, you get a beautiful red ring impact effect. The first such panel is the one that activates the light-bridge in level 2.

You get a similar effect with a shotgun (e.g. you can see it in level 8), though it's not as dynamic. You also get the effect with a chain-gun, though you usually won't have one nearby.

The impact effect with a plasma weapon isn't bad either - quite different though. This makes me wonder what other impact effects I haven't seen. Note to self: must shoot more fixtures!