My father described Christmas lights as being at least two open circuits in series.
@james_s : Over here in Brexitland, we kinda gave up on the trauma of 'Dad' fixing the xmas lights the old fashioned way. Now every tree and house is strung with LEDs. PSUs are tiny switch mode boxes, not those solid brick transformers that will break concrete, and toes, when dropped. Compared with incandescent lamps, LEDs are so cheap there is no incentive to treasure and maintain lamps from year to year. And certainly no need to hold a mix of replacement bulbs at the correct rating. Some local councils recycle defunked lights to keep copper and plastic out of landfill. Furiously cold white LED's are in vogue this year.
btw, we have some very ancient festive lamps, made in China even back then! Sometimes we gently power these through a dimmer circuit. Pictured are 12 volt chinese lanterns from what we suspect is the mid 1930's. But if you guys have a more accurate date, then please do tell.
Season's Greetings EEVBlog.