Yi Peng, a significant Lanna festival, aligns with the Thai Loy Krathong and transforms northern Thailand with vibrant lights and unique customs. Rooted in Buddhist and local traditions from the 14th century, Yi Peng celebrates the "second full moon" of the Lanna calendar with three days of ceremonial activities. The festival’s origins, as described in ancient chronicles like the Yonok and Jamathewi legends, recount a centuries-old practice among the Mon people of Hariphunchai, who released floating lanterns or sapao on rivers to honor departed relatives after returning to their homeland following a plague. This ritual evolved into today’s Yi Peng tradition, with lantern releases symbolizing gratitude, remembrance, and new beginnings.

The three-day festival includes distinct observances: on the first day, villagers prepare offerings and essentials, followed by a second day of charity and temple offerings. The final day sees the release of krathongs, small floating baskets, on rivers. Yi Peng is also marked by lighting phang prathip (oil lamps), releasing floating lanterns, and decorating temple and home entrances with sum par tua pa, ornate natural gateways made from banana, palm, and sugarcane, often symbolizing the mythical Himavanta Forest. These gateways honor the Buddha's life and are believed to welcome blessings for the household.

The festival includes other customs, such as kite flying, firework displays, and community gatherings for meditation and sermons. Chiang Mai is particularly renowned for its colorful Yi Peng celebrations, drawing locals and visitors to witness the picturesque light displays that illuminate the night sky, making it a truly symbolic and visually stunning event in Thailand’s northern region.