A nav light is so designed as to be visible only from certain directions.
Specifically, you can see the problem should that green, starboard nav light be visible from left of the aircraft!
Nav lights are arranged so that when they can be seen from another aircraft, they convey certain positional info on the aircraft showing them.
From memory is it 140 degrees from parallel to the centreline?
That wee 'fence like' thing is to make sure you can't see the nav light from the 'wrong' side.
Last edited by AtomKraft; 16th Apr 2013 at 20:27.