This is the 4534th most frequent French word.
lumineux
Bright or luminous.
In this sentence, "lumineuse" is used to describe the room being bright and filled with light, which comes from the large windows.
La pièce est lumineuse grâce aux grandes fenêtres.
The room is bright thanks to the large windows.
Here, "lumineux" describes the smile as being bright and radiant, both literally and figuratively evoking positivity.
Son sourire lumineux illuminait toute la pièce.
Her bright smile lit up the whole room.
In this case, "lumineux" is used metaphorically to describe the concept as being enlightened or exceptionally clear and creative.