Feast of Lights is a two day holiday that occurs on the last day of the old year (the 28th of Danu) and the first day of the new year (the 1st of Taisham.) Danu 28th is the winter solstice, the shortest day of the year.
The Feast of Lights is celebrated in every nation with lamps and candles filling windows, homes, even anchored ships. There are sometimes parades of people carrying lanterns through the streets and always, everywhere, are there joyous celebrations.
Cairhien has a unique way to celebrate, for this is the only time the people of Cairhien are given breaks. For two days, all social barriers are broken, and everyone goes wild while music and dancing flow through the streets. One of the tenets of the holiday is that any man can kiss any woman, and any woman can kiss any man, and nobles and commoners alike are seen in states of undress from the waist up. At the end of the feast, everyone returns to their normal classes and duties, with no acknowledgment that anything occurred.
The second day of Feast of Lights is called Firstday, on which it is traditional to give alms generously.
Another name for the holiday of Hanukkah is the Festival of Lights. Similarly the holiday Diwali is also known as the Festival of Lights.
Many, if not most, cultures have celebrations of rebirth, triumph of light over darkness, or another theme that ties into observance of the winter solstice.