Original sentence: In practice, a certain amount of visibility is acceptable, as noted above.It would appear that achieving a perfectly concealed (100%) hole, where an object could be placed and concealed, is not probable.The goal then is to create no discernible difference between a concealment volume of space and the propagation of electromagnetic waves through empty space.The problem is the following: in order to carry images, light propagates with a continuous range of directions.The range of the refractive index of the dielectric needs to be across a wide spectrum to achieve concealment with the illusion created by wave propagation across empty space
Edited sentence: In practice, a certain amount of acceptable visibility occurs, as noted above.It would appear that achieving a perfectly concealed (100%) hole, where an object could be placed and hidden from view, is not probable.The goal then is to create no discernible difference between a concealed volume of space and the propagation of electromagnetic waves through empty space.The problem is the following: in order to carry images, light propagates in a continuous range of directions.The range of the refractive index of the dielectric (optical material) needs to be across a wide spectrum to achieve concealment, with the illusion created by wave propagation across empty space