Loi Krathong coincides with the Lanna (northern Thai) festival known as Yi Peng (Thai: ยี่เป็ง). Yi means "two" and peng means a "full moon day". Yi Peng refers to the full moon day in the second month according to the Lanna lunar calendar (the twelfth month according to the Thai lunar calendar).[3]
Swarms of Lanna-style sky lanterns (khom loi (Thai: โคมลอย), literally: "floating lanterns") are launched into the air where they resemble large flocks of giant fluorescent jellyfish gracefully floating through the sky. The festival is meant as a time for tham bun (Thai: ทำบุญ), to make merit. Khom loi are made from a thin fabric, such as rice paper, stretched over a bamboo or wire frame, to which a candle or fuel cell is attached. When the fuel cell is lit, the resulting hot air is trapped inside the lantern and creates enough lift for the khom loi to float up into the sky. People also decorate their houses, gardens, and temples with khom fai (Thai: โคมไฟ), intricately shaped paper lanterns which take on different forms