Your example applies to fast vehicles and for a brief moment to signal a change in speed and direction. You do not have constant flashing lights on the car do you? This discussion is a bout a much slower bicycle and for this reason flashing lights is only allowed In EU at a interval of 200/min and ONLY in the rear and ONLY because they've tried to harmonise various different national rules! If you've ever been riding behind a bike with flashing light for any length of time you'd know how frustrating it is! Any rider using flashing light during a brevé/century are either thrown out of the pack or bullied until he either change settings or ride in the back and for very good reason! Meeting a cyclist with flashing front lights is even more of a nightmare and illegal in the EU. The reason is the same, the eye cant adjust and therefore unable make out the space in front of you as well as the position of the oncoming cyclist. I had a very near miss just the other week and made sure that 'plunker' got the message!