What does the 'Design object' checkbox do?
If an object is classed as a 'design object', calculation results ignore the presence of the object.
If an object is not classed as a 'design object' it is treated as a 'real object', calculation results will show the effect of the object with resultant lower illuminance levels due to shadowing.
The 3D luminance view will be the same regardless of the state of the checkbox.