The HPS do have very typical action when the bulb get near end of the life they will cycle on / off due the arc voltage requirement.
over the time the arc voltage rise and when get to the point where the ballast can not able keep the arc on it will go out when cool off it will relit with high voltage starter.
There are few non cycling HPS on market so when they get near burn out useally what they will do is change colour itself going from orange to white-bleuish colour or complety disabled the bulb interally one of the two way.
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)