Energy Efficiency & Sustainability Flashcards

Which lighting control strategy saves the most energy in a private office with an occupant who frequently leaves for meetings?

Answer: Occupancy sensor with auto-off

Occupancy sensors automatically turn off lights when the space is unoccupied, directly eliminating waste from forgotten lights.

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?

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.

What does the term 'lighting power density' (LPD) express?

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.

Which ASHRAE/IES standard specifically sets maximum lighting power densities for commercial buildings in the United States?

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.

A parking garage luminaire has an efficacy of 120 lm/W. If the fixture produces 12,000 lumens, what is its wattage?

Answer: 100W

Wattage = lumens ÷ efficacy = 12,000 ÷ 120 = 100W.

Which of the following best describes a 'whole-building energy model' in the context of lighting design?

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.

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?

Answer: $7,500

Rebate = 50,000 kWh × $0.15/kWh = $7,500 per year.