C7 bulbs or C9s? How Christmas lights became a nerdy obsession

Adorning trees with electric lights has been common since the early 1900s. Whether you love them – or love complaining about your neighbours’ – this year their ubiquity and inventiveness has become undeniable
I love Christmas lights. I am writing this in my living room, with no overhead lights on. All the illumination is coming from seven strands of lights – one on the tree, six more around the walls; several hundred bulbs. I love them so much that the ones that aren&rsqu