The way I understand it - say, I'm reading a book using a desk lamp as a light source. Well, I will see the pages almost equally well whether I'm sitting in a small room or in a huge dark castle. The lamp is right here, it does not need to 'fill' the castle.

Again, theoretically the light intensity will be a bit higher in a small room with white ceiling and walls but, by no meas, not even by a factor 2.

regards,
Gena