Sunlight filtered through the louvers into the room.
Tips
usage
Almost always met as part of 百叶窗 (bǎiyèchuāng, 'hundred-leaf window' = Venetian blind / louvered shutter). Plain 叶窗 is rarer and treats 叶 'leaf' as the slat metaphor — each slat is one 'leaf'.
memory
叶 (leaf) + 窗 (window) — a window with rows of leaf-like slats.
