That's right; in the light example the total light on the book would be just a tiny bit higher in the small white room. In a sound measurement though, the strength of the reverberent sound is equal to the strength of the direct sound at the "critical distance"(the total sound is therefore 3dB higher than either at that point)and at longer distances, as the direct sound continues to fall off at 6dB per doubling of distance while the reverberent sound is essentially constant at home distances, the reverberent sound is the principal sound factor.
