First, I was actually surprised to learn that before religious celebrations became a part in the holiday season, there were actual celebrations long before. These celebrations were just that, celebrations on light and birth were very common during the winter darkness. It was actually during this time where the wreaths and mistletoe came to exist and became a tradition! The wreaths were used as decorative pieces much like how they're used today and those date back to being pagan customs. Mistletoe was also part of the pagan custom, having been said that they can have healing powers for anyone who went under one. In some societies in the past they also had a ritual significance.
As for why people put up lights outside their homes well the answer also goes back during Yule which is a festival celebrated by Norsemen. Originally they lit a log, called a Yule log during the festival and that tradition spread throughout Europe. And from there other countries and religions adopted the tradition as symbolizing light and warmth and to ward off evil spirits. Before electricity people also used candles near their windows to welcome travelers.
So overall that's how lots of traditions came to be, isn't that pretty cool? The fact that these iconic traditions actually came about thousands of years ago and how extremely similar their meanings are from then and now. So I hope this little bit of holiday trivia brought some cheer to you and don't forget to follow this quote from one of my favorite Christmas movies during this time of year, "the best way to spread Christmas cheer is singing loud for all to hear"!