What part of speech is brightness?

"Brightness" can be a few different parts of speech, depending on how it's used:

* Noun: When referring to the quality or intensity of light. Example: "The brightness of the sun was blinding."

* Adjective: When describing something as bright. Example: "The room was filled with bright, cheerful colors."

It's important to look at the context to determine which part of speech it is.