Lit fiber

Lit fiber is a fiber-optic connection delivered with the provider's own transmission equipment already active on it, so the customer buys bandwidth — typically a 10G, 100G or 400G wavelength or Ethernet circuit — rather than the physical glass strands themselves. It is the opposite of dark fiber, where the customer leases unlit strands and installs its own optronics to light them. Lit fiber suits tenants who want capacity running quickly without owning transmission gear, and is usually billed as a recurring monthly service; dark fiber suits carriers and hyperscalers who need guaranteed, exclusive capacity for years and will operate their own equipment, often under a long-term indefeasible right of use (IRU). Inside a data center, lit-fiber cross-connects are the default way most tenants reach carriers and cloud on-ramps in the meet-me room, while dark fiber is more common for hyperscaler campus-to-campus links.