Lighting Upgrades

Lighting upgrades represent one of the most cost-effective energy efficiency improvements in commercial buildings, offering direct electrical savings and significant reductions in cooling loads. Modern lighting technologies deliver superior light quality while consuming 50-90% less energy than legacy systems.

LED Retrofits

LED technology has fundamentally transformed lighting efficiency and performance characteristics.

Performance Advantages

LED systems provide multiple benefits over traditional lighting:

Efficacy Improvements:

Incandescent lamps: 10-17 lumens/watt
T12 fluorescent: 60-70 lumens/watt
T8 fluorescent: 85-100 lumens/watt
LED systems: 100-150 lumens/watt (current)
Advanced LED: 150-200 lumens/watt (available)

Heat Generation: LED fixtures convert approximately 95% of input energy to light, with only 5% as heat. This contrasts sharply with incandescent lamps (90% heat) and fluorescent systems (60% heat). Reduced heat output directly decreases cooling loads.

Service Life:

LED rated life: 50,000-100,000 hours
T8 fluorescent: 20,000-30,000 hours
Incandescent: 1,000-2,000 hours

Extended life reduces maintenance labor and material costs.

Retrofit Strategies

Type A: Direct Replacement LED lamps replace existing fluorescent tubes without ballast modification. The existing fluorescent ballast remains energized. This approach minimizes installation cost but sacrifices some efficiency due to ballast losses (5-10%).

Type B: Ballast Bypass LED lamps connect directly to line voltage after ballast removal. This configuration eliminates ballast losses and future ballast failures. Requires electrical modification by licensed electrician.

Type C: External Driver LED system uses dedicated LED driver replacing fluorescent ballast. Provides optimal performance and control compatibility. Most expensive initial cost with highest long-term efficiency.

Complete Fixture Replacement New LED fixtures replace entire legacy system. Allows improved optical design, integrated controls, and superior performance. Highest initial cost with maximum energy savings and light quality.

Color Quality Considerations

Correlated Color Temperature (CCT):

2700-3000K: Warm white (hospitality, residential)
3500-4100K: Neutral white (offices, retail)
5000-6500K: Cool white (industrial, healthcare)

Color Rendering Index (CRI): Minimum CRI of 80 required for most commercial applications. CRI >90 recommended for retail, healthcare, and applications requiring accurate color perception.

Lighting Controls

Advanced controls maximize energy savings by matching lighting output to actual occupancy and daylighting conditions.

Occupancy Sensors

Passive Infrared (PIR): Detect heat signatures from occupant movement. Effective in small enclosed spaces (private offices, restrooms, storage rooms). Require direct line-of-sight to occupants.

Coverage: 500-1,000 sq ft typical Response time: 1-3 seconds False-off rate: <1% in proper applications

Ultrasonic Sensors: Emit high-frequency sound waves and detect Doppler shift from moving objects. Function without line-of-sight, suitable for partitioned spaces. Higher false-on rate than PIR.

Coverage: 600-1,200 sq ft typical Sensitivity adjustable for application

Dual-Technology Sensors: Combine PIR and ultrasonic detection. Light turns ON when either technology detects occupancy. Light turns OFF only when both technologies confirm vacancy. Minimizes both false-on and false-off events.

Time Delay Settings:

Offices: 10-15 minutes
Conference rooms: 10-15 minutes
Restrooms: 5-10 minutes
Storage areas: 5-10 minutes
Warehouses: 15-30 minutes

Longer delays reduce lamp cycling in spaces with intermittent occupancy.

Daylight Harvesting

Photosensors measure available daylight and automatically dim electric lighting to maintain target illuminance levels.

Open-Loop Systems: Sensor faces window or skylight, measuring incident daylight but not total workplane illuminance. Lower cost but requires calibration and may not account for interior reflections.

Closed-Loop Systems: Sensor measures total workplane illuminance including both daylight and electric light. Self-calibrating and more accurate. Higher installed cost.

Dimming Response: Continuous dimming provides smooth transitions and maximum energy savings. Step dimming (2-4 levels) offers lower cost with slightly reduced savings.

Energy Savings Potential:

Perimeter zones (15 ft from windows): 30-60% lighting energy reduction
Top-floor zones (skylights): 40-70% lighting energy reduction
Interior zones: Minimal benefit from daylighting

Scheduling and Time Controls

Time Clock Controls: Simple ON/OFF scheduling based on time of day and day of week. Appropriate for spaces with predictable occupancy patterns.

Astronomical Time Clocks: Automatically adjust switching times based on sunrise/sunset calculations. Eliminate seasonal manual adjustments for exterior lighting.

Sweep Controls: Gradual dimming or flashing warning before automatic shut-off. Allows occupants to override scheduled OFF events. Typical warning: 30-60 seconds before shut-off.

Personal Tuning and Task Lighting

Individual Dimming Control: Allow occupants to adjust lighting levels at workstations. Studies show 20-30% energy reduction when occupants can select preferred light levels, as many choose less than design maximum.

Task/Ambient Lighting: Provide high illumination only where needed (task lighting) while maintaining lower ambient levels. Reduces total lighting power density.

Typical implementation:

Ambient lighting: 200-300 lux
Task lighting: 500-750 lux (additional)

Daylighting Integration

Daylighting reduces electric lighting demand while providing psychological benefits and improving occupant satisfaction.

Daylighting Metrics

Daylight Factor (DF): DF = (Interior illuminance / Exterior illuminance) × 100%

Target values:

2-5% DF: Adequate daylighting for most tasks
5% DF: Excellent daylighting, potential for glare

Spatial Daylight Autonomy (sDA): Percentage of floor area receiving ≥300 lux for ≥50% of occupied hours from daylight alone.

Target: sDA₃₀₀,₅₀% ≥ 55% (LEED v4 requirement)

Annual Sunlight Exposure (ASE): Percentage of floor area receiving ≥1,000 lux for ≥250 occupied hours per year. Metric for glare potential.

Target: ASE₁₀₀₀,₂₅₀ ≤ 10%

Daylighting Strategies

Sidelighting: Windows provide daylight penetration approximately 1.5-2.0 times the head height of the window. For 9 ft ceiling, effective daylight zone extends 13-18 ft from window wall.

Toplighting: Skylights distribute daylight more uniformly than sidelighting. Effective for single-story buildings and top floors of multi-story buildings. Potential for excessive heat gain requires careful glazing selection.

Light Shelves: Horizontal surfaces at window mid-height reflect daylight to ceiling, improving penetration depth. Exterior shelves provide shading for lower window portion. Interior shelves enhance distribution without weather exposure.

Glazing Selection: Visible light transmittance (VLT) versus solar heat gain coefficient (SHGC) balance determines daylight delivery and thermal performance.

High-performance glazing:

VLT: 0.50-0.70
SHGC: 0.25-0.40
VLT/SHGC ratio: >1.5 (daylight efficiency)

Cooling Load Reduction

Lighting system efficiency improvements directly reduce building cooling loads.

Heat Gain Calculations

Instantaneous Heat Gain: q = W × Ful × Fsa

Where:

q = heat gain (Btu/hr)
W = installed lighting power (watts)
Ful = lighting use factor (fraction of lights operating)
Fsa = special allowance factor (1.0 for recessed/vented fixtures)

Conversion: 1 watt = 3.41 Btu/hr

Cooling Load from Lighting: Lighting heat gain does not immediately become cooling load. Radiant fraction absorbs into building mass, releasing heat over time. Cooling load calculation requires radiant time series method or equivalent.

Typical split:

Fluorescent/LED: 40-60% radiant, 40-60% convective
Incandescent: 80% radiant, 20% convective

Savings Example

Baseline System:

2W/sq ft fluorescent lighting
50,000 sq ft office space
Total lighting load: 100 kW
Heat gain: 341,200 Btu/hr
Operating hours: 3,500 hr/year

LED Retrofit:

0.8 W/sq ft LED lighting
Total lighting load: 40 kW
Heat gain: 136,480 Btu/hr
Heat gain reduction: 204,720 Btu/hr (17 tons)

Energy Savings: Lighting energy: 60 kW × 3,500 hr = 210,000 kWh/year Cooling energy: 17 tons × 0.8 kW/ton × 1,200 equivalent full-load hours = 16,320 kWh/year Total savings: 226,320 kWh/year

At $0.12/kWh: $27,160/year

HVAC System Interaction

Cooling System Downsizing: New construction projects incorporating efficient lighting can reduce chiller capacity requirements. Each 12,000 Btu/hr lighting load reduction eliminates 1 ton of cooling capacity.

Typical savings: $800-1,200 per ton eliminated

Heating Season Impact: Reduced lighting heat gain increases heating loads during winter. In most climates, cooling savings exceed heating penalties due to:

Lower cost of heating energy versus cooling energy
Reduced operating hours in heating mode versus cooling mode
Alternative heat sources available (perimeter heating systems)

Lighting Power Density (LPD)

LPD quantifies installed lighting power relative to floor area, providing metric for energy code compliance and efficiency comparison.

Calculation Methods

Building Area Method: LPD = Total interior lighting power (W) / Gross floor area (sq ft)

Simple calculation using whole-building allowance. Less accurate but easier to apply.

Space-by-Space Method: LPD calculated separately for each space type using specific allowances.

Total allowed power = Σ (Space area × Space LPD allowance)

More accurate, rewards efficient design in high-use spaces.

ASHRAE 90.1-2019 LPD Allowances

Building Area Method (W/sq ft):

Office: 0.82
Retail: 1.26
School: 0.87
Healthcare: 1.00
Warehouse: 0.48
Hotel/Motel: 0.82

Common Space Types (W/sq ft):

Corridor: 0.41
Office - enclosed: 0.98
Office - open: 0.61
Conference room: 1.16
Classroom: 1.07
Lobby: 0.82
Stairway: 0.49
Storage: 0.38

LPD Reduction Strategies

Efficient Sources: LED technology provides same illuminance with lower installed wattage compared to fluorescent or HID systems.

Optical Design: High-performance fixtures with superior light distribution reduce number of fixtures required to achieve target illuminance.

Zoning: Separate switching for perimeter zones, task areas, and circulation spaces allows selective operation.

Maintained Illuminance: Design for end-of-life lamp output rather than initial output. Most spaces are over-lit when using new lamps. Light loss factor (LLF) accounts for dirt accumulation and lamp depreciation.

Typical LLF: 0.70-0.85

Initial design at target illuminance with LLF consideration reduces installed power by 15-30%.

Economic Analysis

Lighting upgrades typically offer excellent return on investment with short payback periods.

Simple Payback Calculation

Payback = Initial cost / Annual savings

Typical Ranges:

LED lamp retrofits: 2-4 years
Complete fixture replacement: 4-8 years
Occupancy sensors: 1-3 years
Daylight harvesting: 5-10 years

Life Cycle Cost Analysis

Full economic evaluation includes:

Initial equipment and installation costs
Energy cost savings (electricity and cooling)
Maintenance cost savings (re-lamping, ballast replacement)
Utility rebates and incentives
Discount rate for present value calculation

Net present value (NPV) calculation over 15-20 year analysis period typically shows positive returns for comprehensive lighting upgrades.

Utility Incentives

Many utilities offer prescriptive rebates for lighting upgrades:

LED fixtures: $15-50 per fixture
Occupancy sensors: $20-40 per sensor
Daylight harvesting: $30-75 per controlled fixture

Custom incentive programs may provide $0.08-0.15 per kWh saved annually for comprehensive projects.

Implementation Considerations

Power Quality: LED drivers can introduce harmonic distortion. Specify drivers with <20% total harmonic distortion (THD) to minimize electrical system impact.

Flicker: Low-quality LED systems may exhibit visible flicker. Specify fixtures with <5% flicker for office environments and <1% for video/photography applications.

Dimming Compatibility: Verify dimming driver compatibility with control systems. 0-10V analog dimming most common for commercial applications. DALI (Digital Addressable Lighting Interface) provides advanced control capabilities.

Emergency Lighting: Ensure code-required emergency and egress lighting remains functional during lighting retrofits. Battery backup or emergency circuit separation required.

Components

Led Lighting Conversion
Occupancy Sensors Controls
Daylight Harvesting Controls
Task Lighting Strategies