The Wii Zapper is not a Light gun:
This is how a light gun work: The "light gun" is so named because it uses light as its method of detecting where on screen the user is targeting. The name leads one to believe that the gun itself emits a beam of light, but in fact most light guns actually receive light through a photodiode in the gun barrel.
There are two versions of this technique that are commonly used, but the concept is the same: when the trigger of the gun is pulled, the screen is blanked out to black, and the diode begins reception. All or part of the screen is painted white in a way that allows the computer to judge where the gun is pointing, based on when the diode detects light. The user of the light gun notices little or nothing, because the period in which the screen is blank is usually only a fraction of a second.
The Wii Zapper will use the Wii mote which instead of sensing where the gun should be pointing, instead is the actual item that is sending the light to be sensed, if that makes sense. I am personally thrilled about the wii zapper and think it'll be much better than a light gun. Also the games coming out will be amazing for it. Umbrella Chronicles, Ghost Squad, Medal of Honor, then of course Duck Hunt, Wild Gunman, and Hogans Alley. I'm just crossing my fingers for Gumshoe.