The definition of a lighthouse varies from person to person, from lighthouse authority to lighthouse authority. Is a white box with a light on top a lighthouse? A skeletal tower with a light? Most people, I feel, appreciate the classical tower lighthouse and regard anything else as 'not a proper lighthouse.'
I agree with Russ Rowlett in his Lighthouse Directory that a lighthouse ought to be substantial. He suggests minimum dimensions and I can't really argue. I would add though, that I believe one should be able to enter a lighthouse, as per the 'house' part of the word.
Thus, as can be seen in the wonderful photograph above, the Bangor Pier Head light should be considered a true lighthouse. I believe the guy inside is Peter Scott, who is, or at least was, Duty Berthing Master at Bangor Marina and also the man responsible for servicing the light.
I use this post as an excuse to show some more photographs of one of Ireland's two truly red lighthouses!