|Christ Church Cathedral in Dublin|
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In Ireland it's traditional to put a lit candle (one) in a window to welcome the holy family. Here are some more traditions from Holidays Kaboose.
In many areas, on Christmas Eve, a lit candle is placed in a window (nowadays it can be an electric light!). This goes back to traditions of hospitality in ancient times. The idea is to help light the way of the Holy Family or any other poor traveller who is out on that night. There can be a White Christmas, but snowfalls are rarely heavy. As in many countries, it is very important for family members to be together for Christmas Eve and Christmas Day.