how to find circuit breaker for exterior light
Turn off half the panel

And go see if the light is still on.  You now know which half of the panel it is.

Turn off half those breakers.   You now know which quarter of the panel it is.  

Note that you do not need to see the light go out.  If it remains on, that tells you it's in the "unturned off" half of the breakers you are testing. 

Now turn off half of the quarter.  Still on? That means it's in the half of the quarter (1/8)  you did not turn off.  Divide that in two (1/16) and go again. 

You should be able to get there in five, maybe six on a big panel.