Dark Fiber vs Lit Services: A Cost Comparison for Data-Heavy Enterprises

SpendWire Team•3 min read•November 11, 2026

Dark fiber costs more upfront but saves 40-70% over 10 years for bandwidth-intensive organizations. Here is the full analysis.

For enterprises moving large amounts of data between locations, the choice between dark fiber and lit services significantly impacts long-term costs. Dark fiber (unlit, customer-owned wavelengths) requires more upfront investment but delivers dramatically lower per-megabit costs at scale.

Understanding the Options

Dark Fiber

You lease the raw fiber optic strand from a provider. You supply and manage your own optical networking equipment. You control the bandwidth, the protocol, and the upgrade path. The fiber provider simply maintains the physical cable.

Lit Services

The carrier provides a complete, managed circuit with a specific bandwidth. They own and manage the optical equipment at both ends. You get a port at a guaranteed speed with an SLA. Examples include MPLS, dedicated Ethernet, and wavelength services.

Cost Comparison: 10 Gbps Connection Between Two Sites

Lit 10 Gbps Ethernet

Monthly recurring: $4,000-12,000 depending on distance and carrier

Installation: $2,000-10,000

Equipment: included (carrier-managed)

5-year cost: $252,000-730,000

10-year cost: $492,000-1,450,000

Dark Fiber (same route)

Monthly recurring: $1,000-3,000 per strand pair

Construction/IRU (if new build): $15,000-50,000 per mile

Optical equipment (both ends): $15,000-40,000

5-year cost: $90,000-230,000

10-year cost: $150,000-410,000

The Multiplier Effect

The real power of dark fiber is scalability. Once you have the fiber, upgrading from 10 Gbps to 100 Gbps only requires upgrading the optical equipment at each end (roughly $30,000-60,000). With lit services, 100 Gbps means a new contract at 5-10x the monthly cost.

When Dark Fiber Makes Sense

Data center interconnects moving 10+ Gbps

Healthcare or financial organizations with massive data transfer requirements

Organizations planning to scale bandwidth significantly over 5-10 years

Metro-area connections (under 50 miles) where fiber is available

Situations requiring complete control over security and encryption

When Lit Services Win

Low bandwidth needs (under 1 Gbps)

Short contract terms (under 3 years)

Locations without existing dark fiber routes (construction costs change the math)

Limited IT staff to manage optical networking equipment

Need for carrier-managed SLAs with guaranteed uptime

Finding Dark Fiber

Dark fiber availability varies dramatically by geography. Major metro areas like New York, Chicago, Dallas, and Los Angeles have extensive dark fiber networks. Suburban and rural areas may have limited or no options. Providers to evaluate:

Zayo: largest dark fiber network in the US

Crown Castle Fiber: strong in metro areas

Windstream: regional availability

Local CLECs and utility companies: often have fiber assets from decades of infrastructure investment

The SpendWire Angle

Before committing to dark fiber or lit services, audit your current WAN costs across all locations. SpendWire identifies circuits where you are paying lit-service premiums for bandwidth you could deliver more cost-effectively on dark fiber, and vice versa. The optimal strategy is usually a mix of both, with dark fiber for high-bandwidth routes and lit services for lower-bandwidth or shorter-term needs.

dark fiberlit servicesbandwidthnetworkingdata center