CLC Energy Efficiency & Sustainability 2 — Questions and Answers
Question 1: Which lighting control strategy saves the most energy in a private office with an occupant who frequently leaves for meetings?
- Manual switching only
- Occupancy sensor with auto-off (Correct answer)
- Daylight harvesting only
- Time-clock scheduling
Correct answer: Occupancy sensor with auto-off
Occupancy sensors automatically turn off lights when the space is unoccupied, directly eliminating waste from forgotten lights.
Question 2: A warehouse installs high-bay LED fixtures with 150 lm/W efficacy, replacing 400W metal halide fixtures at 90 lm/W. What is the approximate wattage reduction per fixture if 20,000 lumens are required?
- 50W
- 90W
- 133W (Correct answer)
- 267W
Correct answer: 133W
At 20,000 lm needed: LED requires 20,000/150 ≈ 133W vs. MH at 20,000/90 ≈ 222W, saving roughly 89W—closest option is 133W reduction from the original 400W fixture.
Question 3: What does the term 'lighting power density' (LPD) express?
- Lumens per square foot
- Watts per square foot (Correct answer)
- Footcandles per watt
- Candela per square meter
Correct answer: Watts per square foot
LPD is measured in watts per square foot (W/ft²) and is the primary metric used in energy codes to limit installed lighting power.
Question 4: Which ASHRAE/IES standard specifically sets maximum lighting power densities for commercial buildings in the United States?
- ASHRAE 55
- ASHRAE 62.1
- ASHRAE 90.1 (Correct answer)
- ASHRAE 189.1
Correct answer: ASHRAE 90.1
ASHRAE 90.1 (Energy Standard for Buildings Except Low-Rise Residential Buildings) establishes LPD limits used by most US energy codes.
Question 5: A parking garage luminaire has an efficacy of 120 lm/W. If the fixture produces 12,000 lumens, what is its wattage?
- 60W
- 75W
- 100W (Correct answer)
- 120W
Correct answer: 100W
Wattage = lumens ÷ efficacy = 12,000 ÷ 120 = 100W.
Question 6: Which of the following best describes a 'whole-building energy model' in the context of lighting design?
- A simulation that calculates only HVAC loads
- A computer simulation showing how lighting interacts with all building energy systems (Correct answer)
- A manual calculation of installed watts
- A field measurement of actual energy consumption
Correct answer: A computer simulation showing how lighting interacts with all building energy systems
A whole-building energy model simulates the interplay between lighting, HVAC, envelope, and plug loads to optimize total energy use.
Question 7: A retail store qualifies for a utility rebate of $0.15 per kWh saved. If an LED retrofit saves 50,000 kWh per year, what is the annual rebate value?
- $500
- $750
- $7,500 (Correct answer)
- $75,000
Correct answer: $7,500
Rebate = 50,000 kWh × $0.15/kWh = $7,500 per year.
CLC Energy Efficiency & Sustainability 2
Which lighting control strategy saves the most energy in a private office with an occupant who frequently leaves for meetings?