Two architectures for emergency lighting in a commercial building: each fixture has its own battery, or all emergency lighting runs from one centralized DC battery system. Each has trade-offs.
Unit equipment
Each emergency fixture has its own integral battery. When AC power fails, the fixture switches to its battery and operates for 90 minutes. Common in retrofits and small installations.
Pros
- Simple installation — no central infrastructure needed
- Failure of one fixture doesn't affect others
- Lower upfront cost for small applications
Cons
- Battery replacement is per-fixture maintenance, often at ladder height
- Inconsistent battery performance across the building over time
- No centralized monitoring of system health
- Higher long-term cost (every fixture has its own battery to replace every 3-7 years)
Central battery
One central DC battery system powers all emergency lighting throughout the building via low-voltage wiring. When AC fails, the central system supplies emergency power to every connected fixture, exit sign, and ELC-equipped general lighting fixture.
Pros
- Centralized maintenance — replace batteries in one location, accessible at floor level
- Consistent emergency performance across the building
- Cloud monitoring (Sage Live™) gives real-time status and fault alerts
- Lower long-term cost — fewer batteries to replace, fewer points of failure
- Aesthetic — emergency fixtures don't need bulky integral battery housings
Cons
- Higher upfront infrastructure cost
- Wiring requires planning during initial design
- A failure at the central system can affect more fixtures (mitigated by sizing and redundancy)
When to spec central battery
Central battery is the right answer for: multi-floor commercial buildings, projects where long-term maintenance cost matters, applications where centralized monitoring is required (data centers, hospitals, federal facilities), and any project where the architect wants emergency lighting that's visually consistent with the design.
When to spec unit equipment
Unit equipment makes sense for: small retrofits, short-term installations, single-room applications, and locations where running new low-voltage infrastructure isn't feasible.
Sage's approach
Sage's central battery line (Keystone, Volta, Olympus) is the anchor of the product line. Most Sage Luminaires, SCB Fixtures, and Exits operate as remote (RE) units off the central battery — though battery-backup (BB) variants exist for unit equipment retrofits.