This is the 8701st most frequent Japanese word.
明るかっ
"明るかっ" is the stem form of "明るかった," meaning "was bright" or "was cheerful" in English.
In this sentence, "明るかった" is used to describe the brightness of the room, signifying a literal sense of physical light.
部屋が明るかったので読書が楽でした。
Since the room was bright, it was easy to read.
Here, "明るかった" is employed figuratively to describe someone's optimistic and lively personality.
彼女は性格が明るかったので人気者でした。
Because she had a cheerful personality, she was popular.
In this sentence, "明るかった" is used to describe the brightness of the sky, indicating clear and sunny conditions.