Hi. I helped my neighbour putting up (quite old, no LEDs) strings of Christmas lights and noted that some of them (different brands) are connected in parallel, others in series. Inevitably, we found several of the serial strings not working due to defective bulbs. We replaced the visibly broken ones and thus were able to fix some of the strings, but my neighbour trashed most of the non-working ones with 50+ bulbs, heavily swearing and promising to replace them with LED next year. I wonder why light strings in series even exist. Is there some essential advantage to this kind of wiring that makes up for the fact that one broken bulb interrupts the total current? I also found that apparently there exist newer products with bulbs in series that still work if some of them break. How does this work?