Editing Light gun (section)

===Sequential targets===
The first detection method, used by the NES Zapper, involves drawing each target sequentially in white light after the screen blacks out. The computer knows that if the diode detects light as it is drawing a square (or after the screen refreshes), then that is the target at which the gun is pointed. Essentially, the diode tells the computer whether or not the player hit something, and for <var>n</var> objects, the sequence of the drawing of the targets tell the computer which target the player hit after 1 + ceil(log<sub>2</sub>(<var>n</var>)) refreshes (one refresh to determine if any target at all was hit and ceil(log<sub>2</sub>(<var>n</var>)) to do a [[Binary search algorithm|binary search]] for the object that was hit).<ref name="DuckFeedZapper">{{cite web|url=https://www.cs.columbia.edu/~sedwards/classes/2011/4840/reports/Duck-Hunt.pdf|title=DuckFeed: An Embedded Take on Duck Hunt Columbia University, Spring 2011 CSEE 4840: Embedded System Design|last1=Teger|first1=Daniel|last2=Rogowski|first2=Scott|date=May 13, 2011|page=5|url-status=dead|archive-url=https://web.archive.org/web/20180623220601/http://www1.cs.columbia.edu/~sedwards/classes/2011/4840/reports/Duck-Hunt.pdf|archive-date=June 23, 2018|access-date=Jan 21, 2015|last3=Dinerman|first3=Julie|last4=Ramkishun|first4=Kevin}}</ref>

A side effect of this is that in some games, a player can point the gun at a light bulb or other bright light source, pull the trigger, and cause the system to falsely detect a hit on the first target every time. Some games account for this either by detecting if all targets appear to match or by displaying a black screen and verifying that no targets match.<ref name="DuckFeedZapper"/>