It is often reflected by the books of Physics in the longest chapters of Light and Optics under the article of "Opacity and Reflection" that: if you do not want to transmit the beams of lights through any medium --just increase its opacity." Application: If you are irritated by someone in the world of digitalized society and wish to do something to get rid of just use the " block " option--their lights won't transmit to causes interference.(yeah physics wala interfence h)