CEM Lighting Systems 2 — Questions and Answers
Question 1: A warehouse currently uses 400W metal halide fixtures. Replacing them with 150W LED high-bays maintains light levels. What is the percentage energy reduction?
- 50%
- 62.5% (Correct answer)
- 37.5%
- 75%
Correct answer: 62.5%
Energy reduction = (400-150)/400 × 100 = 62.5%.
Question 2: Which lighting control strategy automatically reduces output based on available daylight near perimeter windows?
- Occupancy sensing
- Daylight harvesting (Correct answer)
- Demand response dimming
- Task tuning
Correct answer: Daylight harvesting
Daylight harvesting uses photosensors to dim electric lights as natural light increases.
Question 3: The Color Rendering Index (CRI) measures which lamp characteristic?
- Lamp lumen depreciation over time
- Accuracy of color appearance compared to a reference source (Correct answer)
- Correlated color temperature in Kelvin
- Luminous efficacy in lumens per watt
Correct answer: Accuracy of color appearance compared to a reference source
CRI rates how accurately a light source renders object colors relative to a reference illuminant on a 0–100 scale.
Question 4: An office space requires 50 foot-candles at the work plane. The room has an area of 2,000 sq ft and luminaires with 3,200 lumens each. Using a CU of 0.65 and LLF of 0.80, how many luminaires are needed?
- 48
- 60 (Correct answer)
- 54
- 72
Correct answer: 60
N = (50 × 2000) / (3200 × 0.65 × 0.80) = 100,000 / 1,664 ≈ 60 luminaires.
Question 5: Which term describes the fraction of lamp lumens that actually reach the work plane, accounting for fixture efficiency and room geometry?
- Light Loss Factor (LLF)
- Coefficient of Utilization (CU) (Correct answer)
- Luminous Efficacy
- Lamp Lumen Depreciation (LLD)
Correct answer: Coefficient of Utilization (CU)
The Coefficient of Utilization (CU) represents the ratio of lumens reaching the work plane to total lamp lumens.
Question 6: LED drivers with 0-10V dimming protocol dim a fixture to what minimum output level before the light turns off?
- 0%
- 1%
- 10% (Correct answer)
- 5%
Correct answer: 10%
In 0-10V dimming, 1V corresponds to the minimum dim level (typically ~10%) and 10V is full output; below 1V the fixture switches off.
Question 7: A facility manager wants to reduce lighting power density (LPD) to comply with ASHRAE 90.1. Which metric directly expresses LPD?
- Lumens per square foot
- Watts per square foot (Correct answer)
- Foot-candles at the task plane
- Candela per square meter
Correct answer: Watts per square foot
Lighting Power Density (LPD) is expressed in watts per square foot (W/ft²) and is the standard metric in ASHRAE 90.1.
CEM Lighting Systems 2
A warehouse currently uses 400W metal halide fixtures.
Replacing them with 150W LED high-bays maintains light levels.
What is the percentage energy reduction?