Bright
Cheerful
い adjective
This is a single kanji plus the hiragana るい. Words that end in い are usually adjectives, and this is no exception. What's the adjective form of bright? It's also bright.
This word has a similar reading to 明かり, but here the kanji is read as あか instead of just あ. Here's a mnemonic to help you remember this:
What's a bright color? 赤 (あか), aka "red," obviously. Think of a really bright あか color when you see 明るい.
今日は外が明るい。
It's bright outside today.
このチームは明るい人ばかりですね。
This team is full of cheerful people.
ジェニーは今日は休みだと分かると、一気に明るくなった。
When Jenny found out it was a holiday today, she lit up all at once.