A Sun (Chinese: 陽光普照) is a 2019 Taiwanese drama film directed and co-written by Chung Mong-hong. The film stars Chen Yi-wen, Samantha Ko, Wu Chien-ho, Greg Hsu, and Liu Kuan-ting. Its story centres on Chen Jian Ho (Wu), a troubled teenager who has been arrested, and Hao (Hsu), Ho's accomplished brother who commits suicide due to familial pressure. It explores Ho's re-entry into society and his father's efforts to acknowledge his son, something he had never done. Juvenile delinquency and suicide are the film's main themes, with visual motifs including light and dark. The film, which incorporates many conventions of Asian cinema, also explores socioeconomic inequality in Taiwan.

The film was conceived after a high-school friend told Chung about a crime he had committed as a teenager. This became the opening sequence, which prefaces the narrative. Chang Yao-sheng was enlisted to co-write the screenplay with Chung, a process which took over a year. Filming began in 2018, with a tight 38-day schedule for budgetary reasons. Chung asked the cast not to consult him about their acting and rehearse on their own, although he would often direct them during filming. He was also the film's cinematographer under the pseudonym of Nagao Nakashima. Lai Hsiu-hsiung edited the film to a runtime of 155 minutes, Chung's longest film by far, and Lin Sheng-xiang composed the score.

A Sun premiered at the Toronto International Film Festival on 6 September 2019, before its theatrical release in Taiwan. The film under-performed financially, as did Chung's previous films. It was released on Netflix in 2020; poor marketing contributed to it not receiving much attention, before Peter Debruge of Variety called it the best film of 2020. The film received many positive reviews for its story, diversity of themes, audiovisual quality, and acting. It received a number of accolades, including 11 nominations at the 56th Golden Horse Awards; it received the Best Feature Film award and the Best Director award for Chung. The film was the Taiwanese entry for Best International Feature Film at the 93rd Academy Awards, where it made the 15-film shortlist.