South-facing lamp lit on Trayodashi evening to Yama, praying for protection from untimely death

Yama Deepam, or Yamadeepdaan, is the offering of a lamp to Yama, the lord of death, on the evening of Kartika Krishna Trayodashi, the day of Dhanteras. The Skanda Purana and Padma Purana say that one who offers a lamp to Yama at the entrance of the home on this evening is not troubled by untimely death (akal mrityu). The rite is linked to the story of King Hima's son, whose bride saved him from the fated serpent by lighting the house with lamps and heaping her ornaments at the door. In another account, Yama's messengers told him they felt pity when taking a young life, and Yama declared that households lighting a lamp for him on this Trayodashi would be spared. A lamp of wheat flour with four wicks is filled with mustard or sesame oil and placed facing south — the direction of Yama — on a heap of grain outside the main door. It is the only day of the year when a lamp is intentionally placed facing south. In South India, Yama Deepam is also lit on Naraka Chaturdashi eve, and it marks the start of the five-day Yama Panchaka.

No fast is required; it is a lamp offering done along with Dhanteras puja.