Subject: how do videogame 'guns' work?

i have always wondered how those video game "guns" worked. an example 
could be Konami's GUNCON, or those "guns" in some of those arcade games 
like Virtuacop or lethal enforcers, of for those old school nintendo kids, 
the gun used in Duckhunt or Hogan's Alley.

my theory is, that the computer accepts only pre-programmed lightwaves or 
certain frequencies-->colors on the screen of the certain targets. once 
the trigger is pulled, the opto-electronic device is connected to the 
circuit, and it acts like a photo diode, responding to the 
colors/lightwaves that the things you should be shooting on the screen 
have. once it recieves a matching fqcy of light, the diode acts as a 
closed switch, then the corresponding response from the computer gives you 
the points (and the dead duck). 

is my theory even close?    

Re: how do videogame 'guns' work?