Just a side not that light in other medium than air travels slower. It's not 300k km/h but ~200k km/h in FR4 microstrip (6"/ns where 1ns is equivalent to 1GHz clock).
translated: "Just an aside: note that the speed that light travels in any medium is slower than it travels in vacuum. Its speed is no longer 3e8 m/s, but a third less in, for example, FR-4 microstrip (a popular prototype board dielectric). The effective speed is about 6 inches per ns, or at least, 6 inches per cycle of a 1 GHz clock."