A dim place is rather dark because there is not much light in it.
黑暗的 • The room was dim and cool and quiet. 这房间昏暗、阴冷且安静。
If you dim a light or if it dims, it becomes less bright.
使变暗; 变暗 • Dim the lighting – it is unpleasant to lie with a bright light shining in your eyes. 把灯光调暗–在刺眼的灯光下躺着不舒服。