Speed of light fibre optic signals which travel 30–40% slower at the speed of light through glass. There are different ways to determine the value of "c". One way is to measure the actual speed at which light waves propagate, which can be done in various astronomical and earth-based setups. However, it is also possible to determine "c" from other physical laws where it appears, for example, by determining the values of the electromagnetic constants "ε" and "μ" and using their relation to "c". Historically, the most accurate results have been obtained by separately determining the frequency and wavelength of a light beam,
Max Planck Institute for the Science of Light Max Planck Institute for the Science of Light The Max Planck Institute for the Science of Light (MPL) performs basic research in optical metrology, optical communication, new optical materials, plasmonics and nanophotonics and optical applications in biology and medicine. It is part of the Max Planck Society and was founded on January 1, 2009 in Erlangen near Nuremberg. The Institute is based on the Max Planck Research Group "Optics, Information and Photonics", which was founded in 2004 at the University of Erlangen-Nuremberg, as a precursor. The institute currently comprises five divisions. The institute currently is organized in five divisions, each