However, it's important to note that "shiner" is often used in a more informal context, usually referring to a bruise or a black eye.
For a more general comparison of brightness or brilliance, you would typically use more shining or brighter.
For example:
* "The sun is shinier today than it was yesterday." (Informal)
* "The new lamp is more shining than the old one." (Formal)
* "The diamonds in her necklace were brighter than the stars." (General comparison)