Loi Krathong coincides with the Lanna (northern Thai) festival known as "Yi Peng" (Thai: ยี่เป็ง). Due to a difference between the old Lanna calendar and the Thai calendar, Yi Peng is held on a full moon of the 2nd month of the Lanna calendar ("Yi" meaning "2nd" and "Peng" meaning "month" in the Lanna language). A multitude 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 by through the sky. The festival is meant as a time for tham bun (Thai: ทำบุญ), to make merit. People usually make khom loi from a thin fabric, such as rice paper, to which a candle or fuel cell is attached. When the fuel cell is lit, the resulting hot air which is trapped inside the lantern creates enough lift for the khom loi to float up into the sky.