Obstruction lights on Tornado

Hi,

This is my first post here, been a avid reader of AFM for years now.

Recently I have been looking at the Tornado in great detail and noticed that some aircraft have what is labelled as an obstruction light just underneath the RWR antenna on the fin. I can see no pattern as to which aircraft have this feature and am no wiser as to its function. Can anyone explain the function of these things.

You can see it on this aircraft whilst other don’t have it.
http://www.airliners.net/open.file/1246216/M/

Regards