Brightness or radiance; the quality of shining or glittering. Can also be used figuratively for sparkle in someone's eyes or expression.
夜空の星の輝きがとてもきれいだった。
The brightness of the stars in the night sky was very beautiful.
彼女の笑顔には特別な輝きがある。
There is a special sparkle in her smile.
宝石の輝きが光を反射した。
The jewel's brilliance reflected the light.