Radiance is a type of glowing: either from a light source like the sun or a healthy, beaming person.
The sun radiates lights, and bright objects that give off light rays have a quality called radiance. The sun's radiance can be felt the strongest in the afternoon. We use lights for their radiance: they brighten rooms and streets. Also, if someone is happy and healthy, we can talk about their radiance. A sign of radiance in a person is a wide smile, and pregnant women are often said to have a glow or radiance because they’re full of life.