"Scotty" wrote in message
...
''lights change characteristics''

how so?

Well ,around here there are lighthouses that were built on convenient
islands but have more recently been replaced with lights on concrete pillars
placed somewhat nearer to the channel. These can have different
characteristics to the disused ones.
But lighted buoys are more likely to be shifted and changed. There was a big
change of light characteristics in most of the world many years ago now when
the IALA system of buoyage was introduced internationally.
The USA did not sign up to this so all your channel buoys are opposite hand
to the rest of the world and AFAIK you do not use the same cardinal light
system to mark offshore obstructions that are familiar elsewhere. :-(