This is controlled by the scripts. Take a look at the two scripts involved.
Light main script: light1.fpi
;Artificial Intelligence Script
;Header
desc = Light Toggle (On By Default)
;Triggers
:state=0:state=1
:state=1,activated=0:state=2,lighton
:state=2,activated=1:state=1,lightoff
;End of Script
Triggerzone main script: plrinzoneactivateused.fpi
;Artificial Intelligence Script
;Header
desc = Plr In Zone, activate entity specified in IF USED
;Triggers
:state=0,plrwithinzone=1:activateifused=1,sound=$0,state=1
:state=1,plrwithinzone=0:state=0
This simple modification to plrinzoneactivateused.fpi will make the light go out when your in the triggerzone and come back on when you leave.
;Artificial Intelligence Script
;Header
desc = Plr In Zone, activate entity specified in IF USED
;Triggers
:state=0,plrwithinzone=1:activateifused=1,sound=$0,state=1
:state=1,plrwithinzone=0:activateifused=0,sound=$0,state=0
Hope this helps.