Here are many origin of Lohri: all that are part of the folklore. The main theme of Lohri, however, is the belief that the cultural celebration of the winter solstice is Lohri. Lohri is meant to be celebrated on the shortest day of the year. An important feature of Lohri is the bonfire. Lighting of the fire is common in the winter solstice festivals in time and the world: it means the return of longer days. For some, the fire has a religious significance, a remnant of ancient origins, perhaps? For others it’s not fire more than a tradition.
Going forward, instead of celebrating Lohri Punjabis celebrate winter solstice occurs on the day, on the last day of the month in which winter solstice takes place. This is due to Lohri Bikrami calendar and creating a link between the twinning of the festival of Makar Sankranti which is celebrated in the Punjab region as Maghi Sangrand.
According to folk lore, in ancient times was Lohri on winter solstice day is celebrated. It is for this reason that people believe that Lohri of night is meant to be the longest night of the year and on the day after Lohri, daylight is meant to increase. The day after Lohri is celebrated as Maghi Sangrand when the days are meant to start getting longer.
However, scientifically, the shortest day of the year around 21-22 December, after which the days start getting longer. Accordingly, winter solstice starts on 21 December or 22 December and Lohri should be celebrated on the day of the winter solstice followed by Maghi Sangrand (Makar) the next day.