it doesnt really matter which way you connect them, assuming they are not ES (edison screw lamps) as ES the centre should be the live, but seeing as yours are all white i should say they are not es, so it doesnt matter (so long as they are all paralell)
It's when you are using the type of ES fitting that have no exposed live parts - some plastic threaded ones have contacts that are only made live when a lamp is fully screwed in.
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