The light gun used by the arcade version of House of the Dead 2 (and I think Virtua Cop 3 and Ghost Squad) also worked the same way as the Wii Remote's pointer, using a camera in the controller to sense infrared LEDs. So the screen doesn't flash white when you pull the trigger on the arcade version of HotD2 like it does on the console version.

Instead of a single bar with two LEDs like on the Wii, there's a row of five LEDs above and below the screen. You can make them out in this video:

https://youtu.be/vmt-UAc28bo?t=192