The most common and most likely answer to this crossword clue is the 7 letter word NERDIER
I've seen this crossword clue in The Times
N
E
R
D
I
E
R
Buddy explains!

The straight part
We know that "less bright" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case less bright = nerdier.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NERDIER mean?
NERDIER adjective- (of a person) Being or like a nerd.
- (of a quality or interest) Of, pertaining to, in the style of, or appealing to nerds.