This is the 690th most frequent Persian word.
روشن
"روشن" means "bright" or "clear" in English.
The word 'روشن' here means 'on', used to indicate the activation of a light source.
چراغ را روشن کن.
Turn on the light.
In this sentence, 'روشن' suggests becoming bright or glowing, here metaphorically referring to the face lighting up due to happiness.
صورتش روشن شد وقتی خبر خوب را شنید.
Her face brightened up when she heard the good news.
Here 'روشن' signifies clarity or understanding, applied metaphorically to concepts.