The characters combine to create a vivid image: “The face (面) is full (满) of a red (红) glow (光).” This isn't just a red face from exertion or embarrassment, but an inner radiance that shines outward, signifying a person who is thriving.
In traditional and modern Chinese culture, one's outward appearance, especially the face's complexion (气色, qìsè), is seen as a direct reflection of their internal health. A ruddy, glowing face is the ultimate sign of good health, strong blood circulation, and abundant energy. A useful Western comparison is the phrase “in the pink” or “glowing with health.” However, a key cultural difference lies in the perception of the color red. In the West, a “red face” can often carry negative connotations of anger (“seeing red”), embarrassment (blushing), or a medical issue like high blood pressure. In the context of 红光满面, the “red glow” (红光) is unambiguously positive, tied to the auspicious cultural symbolism of the color red and the traditional Chinese medicine concept of healthy blood flow and qi. Complimenting someone, especially an elder, on being 红光满面 is to compliment their fundamental vitality.
This idiom is widely used in daily conversation and is considered a warm and positive compliment.