Fiber optic cables transmit data as light signals, unlike copper wires which use electrical signals. The speed of an electrical signal propagating along a cable is usually more like 2/3 the speed of light, because of transmission-line effects. In this context, 'speed' refers to the amount of data that can be transmitted per unit of time. Sound waves in air, light waves in optical fiber or glass, electrical waves in a cable do possess certain bandwidth limitations arising from their medium of. Fiber-optic cables are better than copper wires for signal transmission because they have more bandwidth, they are less susceptible to interference, they are smaller and lighter, and they are more durable.