It is often used in scientific and medical contexts to refer to light or illumination. Here are some examples:
* Luminescence: The emission of light by a substance, not caused by heat.
* Luminous: Emitting or reflecting light.
* Luminary: A person who is highly respected or influential.
* Lumen: A unit of measurement for luminous flux, the amount of light emitted by a source.
Therefore, when you see the prefix "lum," it's a good indication that the word relates to light or brightness.