Emperor Guangzong 明光宗, personal name Zhu Changluo 朱常洛 (1585-1620, r. 1620), the Taichang Emperor 泰昌, was one of the last emperors of the Ming dynasty 明 (1368-1644). He was the oldest son of Emperor Shenzong 明神宗 (the Wanli Emperor 萬曆, r. 1572-1619) and Lady Wang 王恭妃, but Lady Zheng 鄭貴妃, the favourite concubine of Emperor Guangzong, shortly after Changluo's birth drew away the Emperor's attention to Prince Zhu Changxun 朱常洵, whom the emperor esteemed higher than his oldest son, and wished to make heir apparent. There arose a long-lasting struggle among the court ministers whether it was justified to make the younger son heir apparent or not. This quarrel is known as "strife for the root of the dynasty" (zheng guo ben 爭國本). In 1600 finally, Emperor Shenzong made Prince Changluo his heir apparent. In 1615 a certain Zhang Cha 張差 penetrated the compounds of the crown prince's palace, the Ciqing Palace 慈慶宮, with a club in his hand, and killed the eunuch gate attendant of the Heir Apparent. The case was brought to trial and was known in history as the "club-hit case" (tingji an 梃擊案). It was believed that Lady Zheng had attempted to kill the rival of her son. When Emperor Shenzong died, Prince Changluo was enthroned and chose the reign motto Taichang 泰昌 "Grand Brilliance".
Lady Zheng again tried interfering into state affairs and claimed the title of Empress Dowager, which was denied, after severe disputations among the court ministers. Yet her ambitions were not cooled down. She dwelled in the Qianqing Palace 乾清宮, together with Chosen Attendant Li 李選侍.
The only important edict of the Taichang Emperor was the abolition of the court eunuchs' supervision of the mining (kuangshui 礦稅) and trade (queshui 榷稅) tax.
When Emperor Guangzong fell ill, barely a month after his accession to the throne, the Lady sent the eunuch Directorate of Ceremonial (司禮監秉筆兼掌御藥房) Cui Wensheng 崔文昇 with a medicine to cure the illness of the emperor, but his situation aggravated. Shortly after XXX 鴻臚寺丞, Li Kezhuo 李可灼, presented to the emperor a red pill, allegedly rendering immortality, that immediately killed him. The ensuing trial is known as the Red Pill Affair (hongwan an 紅丸案).
Emperor Guangzong was buried in the tomb mound Qingling 明慶陵. His posthumous honorific title is Emperor Xiaozhen 孝貞皇帝, his temple name Guangzong 明光宗. He was succeeded by his oldest son, Prince Youxiao 朱由校, who is known as Emperor Xizong 明熹宗 (the Tianqi Emperor 天啟, r. 1621-1627).