Sky lanterns, also known as Kongming Lantern or Chinese lanterns are airborne paper lanterns that are best known as a tradition found in some Asian cultures. They are traditionally constructed from oiled rice paper on a bamboo frame, and contain a small candle or fuel cell composed of a waxy flammable material. When lit, the flame heats the air inside the lantern, thus lowering its density and causing the lantern to rise into the air. The sky lantern is only airborne for as long as the flame stays alight, after which the lantern sinks back to the ground.
In ancient China, sky lanterns were strategically used in wars. However later on, non-military applications were employed as they became popular with children at carnivals. These lanterns were subsequently incorporated into festivals like the Chinese Mid-Autumn and Lantern Festivals.
Lanna (Northern Thai) people use sky lanterns all year round, for celebrations and other special occasions. One very important festival in which sky lanterns are used is the Lanna festival known as "Yi Peng" which 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). Due to a difference between the old Lanna calendar and the traditional central Thai calendar it coincides with Loi Krathong which is held on the full moon of the 12th month in the traditional Thai lunar calendar. During the Yi Peng festival, a multitude of 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 most elaborate Yi Peng celebrations can be seen in Chiang Mai the ancient capital of the former Lanna kingdom. 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 in to the sky. In addition, people will also decorate their houses, gardens and temples with khom fai intricately shaped paper lanterns which take on different forms.
It is considered good luck to release a sky lantern, and many Thais believe they are symbolic of problems and worries floating away. In recent times, khom loi have become so popular with all Thai people that they have become integrated into the Loi Krathong festival in the rest of country.