Just to add on for others reading your comment: Although metals are opaque, conductors can still be transparent. A few techniques: - Very thin layers (like gra

Just to add on for others reading your comment: Although metals are opaque, conductors can still be transparent. A few techniques: - Very thin layers (like graphene) such that absorption is on the order of a percent - Narrow bandwidth materials that are opaque to infrared but transparent to visible - Bad metals and non-band conductors that have correlated electron hopping from site to site Transparent conductors like ITO are critical materials for displays and solar cells, since light needs to enter/exit one side of the device.