I'd say its hard coz what do you see as intitial action? the date of the patent? the day the company was declared? or the day mr walker found this egg timer or whatever it was and decided to try and make this a lamp or hen the first prototype was done? did you ask mathmos? they sh/could know but they dont even know what lamps they used to make nowadays...cressida cranger would be the one to ask I'd say.