Sefer HaBahir 13

1And Rabbi Bun sat and expounded more, "Why is it written, '[God] forms light and creates darkness' (Isaiah 45:7)? [Since] there is substance in light, it is written, as ‘formation.’ [Since] there is not substance in darkness, it is written as ‘creation.’ As you say, '[God] forms mountains and creates wind' (Amos 4:13). And if you want, say, that light has existence in it, as it is written, 'And Elohim said, ‘Let there be light,’ and there is no existence except by making, [therefore] call it 'formation.' Darkness, since it does not involve making, only separation and setting aside, it is called ‘creation’ [בריאה], as it is said, 'So-and-so became healthy [הבריא].'"