Its pretty much what the title says, If you put a brick on the floor in real life, It has a shadow. In Blockland, The bricks don't. In real life, If you built a house with no windows (which would be kind of weird) it would get dark inside, Even on a sunny day! If you built a house with no windows (again kind of weird) you doesn't get dark.
Personally i think Blockland needs to be more like real life.