Self-luminous refers to objects that emit their own light without needing an external light source. This phenomenon is commonly seen in certain materials, such as phosphorescent or fluorescent substances, which can glow in the dark after being exposed to light. Examples include glow-in-the-dark stars and some types of jellyfish. In nature, some organisms, like fireflies and certain species of deep-sea fish, are self-luminous due to biochemical processes. These creatures produce light through chemical reactions in their bodies, which can serve various purposes, such as attracting mates or deterring predators.