CEM Lighting Systems 5 — Questions and Answers
Question 1: A facility has 500 luminaires each with two 32W T8 lamps and a ballast consuming 6W. What is the total connected lighting load in kW?
- 32 kW
- 35 kW (Correct answer)
- 17.5 kW
- 70 kW
Correct answer: 35 kW
Power per luminaire = 2×32 + 6 = 70W; total = 500 × 70W = 35,000W = 35 kW.
Question 2: Which photometric measurement describes luminous intensity distribution in a plane containing the luminaire's axis, used to generate isolux diagrams?
- Luminance (cd/m²)
- Candlepower distribution curve (Correct answer)
- Exitance (lm/m²)
- Illuminance (lux)
Correct answer: Candlepower distribution curve
Candlepower distribution curves (polar intensity plots) show how a luminaire distributes light in specific planes, enabling isolux calculations.
Question 3: Stroboscopic effect in lighting is a concern primarily because:
- It increases lamp operating temperature
- It can make rotating machinery appear stationary, creating safety hazards (Correct answer)
- It causes lamp lumen depreciation to accelerate
- It reduces the power factor of ballasts
Correct answer: It can make rotating machinery appear stationary, creating safety hazards
When light flickers at frequencies matching the rotation speed of machinery, equipment can appear stationary, posing serious workplace safety risks.
Question 4: A lighting energy audit reveals that a building operates lights 24/7 in spaces unoccupied at night. Installing occupancy sensors reduces operating hours from 8,760 to 5,000 hours/year. If lighting uses 50 kW, what is the annual energy savings at $0.10/kWh?
- $17,600
- $18,800 (Correct answer)
- $25,000
- $43,800
Correct answer: $18,800
Hours saved = 8,760 – 5,000 = 3,760 h; savings = 50 kW × 3,760 h × $0.10 = $18,800.
Question 5: Which commissioning activity verifies that installed lighting controls perform as specified after construction is complete?
- Design-phase load calculation review
- Functional performance testing (Correct answer)
- Lamp photometric testing
- Electrical panel load balancing
Correct answer: Functional performance testing
Functional performance testing (a commissioning process) verifies that sensors, dimmers, and scheduling controls operate correctly under real conditions.
Question 6: When comparing LED to high-pressure sodium (HPS) for outdoor area lighting, LED provides an advantage in:
- Lower initial capital cost
- Instant restrike capability and better color rendering (Correct answer)
- Higher tolerance to extreme cold temperatures
- Longer rated lamp life in all conditions
Correct answer: Instant restrike capability and better color rendering
LEDs strike instantly with no warm-up and offer CRI 70–90+, while HPS requires minutes to restrike after outage and has CRI ~20–25.
Question 7: In the context of energy auditing, a Lighting Power Density (LPD) calculation for a classroom that is 900 sq ft with 14 fixtures at 54W each yields approximately:
- 0.72 W/ft²
- 0.84 W/ft² (Correct answer)
- 1.50 W/ft²
- 0.60 W/ft²
Correct answer: 0.84 W/ft²
LPD = (14 × 54W) / 900 ft² = 756 / 900 = 0.84 W/ft².
CEM Lighting Systems 5
A facility has 500 luminaires each with two 32W T8 lamps and a ballast consuming 6W.
What is the total connected lighting load in kW?