What festival did the ancient Shangyuan Festival refer to?

"Shangyuan Festival" is a traditional festival in China, which originated from Taoism's "Sanyuan Theory". It refers to the Shangyuan Festival (Tianguan Festival and Lantern Festival) on the fifteenth day of the first lunar month, the Zhongyuan Festival (Diguan Festival and Menglan Basin Festival) on the fifteenth day of the seventh lunar month, and the Xiayuan Festival (Shuiguan Festival) on the fifteenth day of the tenth lunar month. The three officials in charge of the upper, middle and lower elements are heaven, earth and man. The "yuan" here refers to the fifteenth day of the lunar calendar.

"Shangyuan Festival" began in the Han Dynasty more than 2000 years ago. During the period of Emperor Wu of the Han Dynasty, the activity of offering sacrifices to "Taiyi God" was scheduled on the 15th day of the first month of the lunar calendar (the birthday of Tianguan Taiyi God). The "One God" is regarded as the supreme god, the god who dominates all things in the universe.

Wu in the Southern Song Dynasty said in Liang Lumeng: "The fifteenth day of the first month is the day when the Shang Dynasty blessed the people." It is said that God bless the people and the county magistrate forgives the sins. And make full use of the first full moon night of the New Year, the bright moon in the sky and the bright lights in special time periods to express good wishes for life. People happily post couplets, one of which is "Many blessings and many celebrations" and the other is "God bless the people" or "The Millennium is from heaven". Because the celestial officials are beaming, the Lantern Festival is to be lit.