1. The streets are brightly lit.

2. These are brightly-lit streets.

Are both the sentences correct?

Why "brightly lit" is not hyphenated in (1)?

Is "lit" in (1) an adjective or past participal used as passive?

I have a lot of confusion about hyphenation. Sometimes it is hyphenated and the same time not.

What are the exact rules?

Please help me.
#1 is correct.

Use the hyphens when the phrase is used to decribe a noun, but not generally after the verb. She attends school part time. (no hyphen). She is a part-time student.

The other style "rule" (and I use the quotations, because this is a style, not a grammar issue, and there are competing prominent style guides) is that you don't hyphenate with an adverb ending with -ly, like brightly lit, even when it does modify a noun.
Students: We have free audio pronunciation exercises.
Hello Grammer Geek!

There were some typing mistakes. I have correted it.

Please check it again.

Thanks for helping me.
I'm going to leave the parts of speech part to someone else - I'm terrible at that.

But the same comments I made about the hyphens still apply. The style guide I follow says to NOT hyphenate -ly words, and you don't do it (regardless of whether there is an -ly) when it does not come immediately before a noun.

1. The streets are brightly lit. ("lit" here an adjective?)
Site Hint: Check out our list of pronunciation videos.