The word "光天化日" is formed by combining the characters 光 (light), 天 (sky), 化 (transform), and 日 (sun) into a fixed four-character idiom. Literally, "光天" means "bright sky" and "化日" means "transformed sun", which together depict a scene of broad daylight with intense sunlight. This literal combination metaphorically conveys the idea of an open, public, and fully visible environment, often used to describe actions occurring in plain sight without secrecy.