How do lighting upgrades affect electrical load in Charleston, SC?

Answered by the Nextech team · November 6, 2026

How lighting upgrades change electrical load (connected load vs peak demand)

Most commercial lighting upgrades reduce connected load because LED fixtures usually deliver similar usable light with fewer watts than older HID, fluorescent, or incandescent systems. Controls—like occupancy sensors, scheduling, and daylight dimming—often reduce coincident peak demand by ensuring fewer fixtures are at full output at the same time.

The load impact is not always a straight reduction. It can increase if the project adds fixtures, raises light levels substantially, adds illuminated signage, or includes drivers/controls and emergency lighting components that weren’t previously present. The most defensible way to quantify the change is a before/after takeoff (fixture count × watts) plus field measurements of amperage on representative circuits.

Worked example (watts kW amps at 277V/120V) + controls

Example (typical math): A sales floor has 80 fixtures.

• Before: 80 150W = 12,000W 1,000 = 12.0 kW
• After LED: 80 60W = 4,800W 1,000 = 4.8 kW

Approximate current (single-phase equivalent): amps watts volts.

• At 277V: 12,000W 277V 43A (before) vs 4,800W 277V 17A (after)
• At 120V: 12,000W 120V 100A (before) vs 4,800W 120V 40A (after)

Controls effect (peak vs connected): Connected load after the retrofit is still 4.8 kW if every fixture can be on at once. But if occupancy/daylight controls mean only ~70% of fixtures are typically at full output during the utility peak window, the coincident lighting demand could be about 4.8 kW 0.70 = 3.4 kW during that period. That difference matters for demand (kW) even though the connected load (kW) on paper is unchanged.

Notes: This is simplified arithmetic to illustrate order-of-magnitude. Real circuits may be multi-phase, have power factor/driver characteristics, and include multiple lighting zones.

Charleston-specific electrical considerations (typical, not guaranteed)

Charleston-area commercial buildings often have electrical and operating realities that make the details of a lighting upgrade matter:

• Demand/peak kW exposure: Many commercial utility rate structures (typical for larger accounts) include demand charges based on the highest measured kW during a billing period. Controls that reduce coincident lighting load during peak hours can help reduce that peak, not just total kWh.
• 277V lighting is common: In many commercial spaces, lighting is served at 277V from 480Y/277V systems. Lower watts reduces amps, which can free capacity on existing breakers and conductors—but voltage compatibility, dimming method, and driver specs still need to match the existing distribution.
• Coastal humidity/corrosion: In coastal South Carolina, humidity and salt air can accelerate corrosion on fixtures, housings, fasteners, and control enclosures (especially in exterior, canopy, loading, or semi-conditioned areas). Specifying appropriate fixture ratings, gasketing, and materials is often important for longevity and reliability.
• Permitting/documentation workflow: Lighting changes that touch branch circuits, emergency/egress lighting, or control systems may require permits/inspections. Having clear fixture schedules, cut sheets, and as-builts helps operations and future troubleshooting.

Checklist to hand to your electrician (load verification + documentation)

• Panel schedule review: Confirm which panels/circuits feed lighting, breaker sizes, conductor sizes, and available capacity.
• Measured load vs nameplate: Take clamp-meter readings on representative lighting circuits (before/after) and compare to fixture/driver nameplate watts and expected diversity.
• Driver/inrush specs: Verify LED driver inrush current, steady-state current, dimming type (010V, phase-cut, DALI, etc.), and compatibility with existing controls.
• Emergency/egress loads: Identify emergency fixtures, battery backup drivers, exit signs, and any required runtime; confirm how they are fed and how they affect circuit loading.
• Controls sequence of operation: Document schedules, occupancy zones, daylight setpoints, and any demand-response or load-shed settings so peak behavior is predictable.
• Permitting/operations package: Provide fixture counts/wattage, one-line or riser notes as applicable, cut sheets, and updated as-builts for maintenance.

Next step: Fort Mill Commercial HVAC & Refrigeration