How Fast Is Light in Fibre Optic?

Light in fibre optic cable travels at 200,000 km/s — two-thirds vacuum speed. The Internet's backbone runs on this; every webpage, every video call, every email crosses oceans on pulses of light through hair-thin glass.

A single subsea fibre-optic cable can carry over 250 terabits per second — enough to transmit the entire Library of Congress in under a second.

• The internet runs on this
• Slower than light in air, but easier to contain