yes
The word brightly is already an adverb.An example sentence with this word is: "the moon shone brightly that night".
the sun shone brightly
It is an adverb. The adjective is simply bright.
The adverb form of the word "bright" is "brightly." It describes an action that is done in a bright manner, such as shining or illuminating. For example, "The stars shone brightly in the night sky."
Comparative and Superlative forms are for Adjectives and brightly is an Adverb, therefore there is no comparative or superlative for brightly. The forms brighter and brightest exist as the comparative and superaltive forms of the adjective bright.
brilliantly
bright
Glow brightly
Glaring.
glow
The adjective bright has the adverb form brightly. The sun is bright. The sun shines brightly.
"The sun shines most brightly on a clear summer's day." Need another one?