'adalah' is optional here, it's used as a copula (linking verb) to connect the two phrases.
You can omit 'adalah', then you'll get a sentence without a verb :
"Dari bumi, lampu jalan (adalah) lebih terang dari bintang-bintang."

'adalah' is mostly used to connect two noun phrases, but it's not restricted to that.
It can also be used to connect with an adjective phrase (like the example above) or to connect with a prepositional phrase (see example below).
Example:
"Satu-satunya cahaya yang ada adalah dari lampu jalan."
"The only light there is, is from the street lights"

'dari lampu jalan' = 'from the street lights" = prepositional phrase.

You’re right.