CEM Lighting Systems and Controls 2 — Questions and Answers
Question 1: What is lumen depreciation?
- The reduction in lamp wattage over time
- The gradual decrease in light output as a lamp ages (Correct answer)
- The increase in color temperature as lamps age
- The decrease in power factor of aging ballasts
Correct answer: The gradual decrease in light output as a lamp ages
Lumen depreciation refers to the reduction in light output that occurs over a lamp's service life due to phosphor degradation and other aging factors.
Question 2: Which ballast type provides the greatest energy savings for fluorescent lamps?
- Magnetic (core-and-coil) ballast
- Electronic high-frequency ballast (Correct answer)
- Reactor ballast
- Autotransformer ballast
Correct answer: Electronic high-frequency ballast
Electronic high-frequency ballasts operate lamps at 20,000+ Hz, eliminating flicker losses and running more efficiently than magnetic ballasts.
Question 3: The Lighting Power Density (LPD) metric is expressed in:
- Lumens per square foot
- Watts per square foot (Correct answer)
- Footcandles per watt
- Candelas per square meter
Correct answer: Watts per square foot
LPD is expressed as watts per square foot (or W/m²) and is used in energy codes to limit installed lighting power in buildings.
Question 4: Task-ambient lighting design saves energy compared to uniform lighting by:
- Using higher-wattage lamps throughout
- Providing higher illuminance only at work surfaces and lower levels elsewhere (Correct answer)
- Eliminating all overhead lighting
- Using only natural daylight for task areas
Correct answer: Providing higher illuminance only at work surfaces and lower levels elsewhere
Task-ambient systems deliver high light levels where needed for visual tasks while maintaining lower ambient levels, reducing total installed wattage.
Question 5: In a lighting retrofit, the simple payback period is calculated as:
- Annual savings divided by installed cost
- Installed cost divided by annual savings (Correct answer)
- Installed cost multiplied by annual savings
- Annual savings multiplied by project lifetime
Correct answer: Installed cost divided by annual savings
Simple payback is the initial investment divided by annual energy and maintenance savings, expressing how many years it takes to recover the cost.
Question 6: High-pressure sodium (HPS) lamps are commonly used in street lighting because they offer:
- Excellent color rendering above CRI 90
- High efficacy and long lamp life (Correct answer)
- Instant restrike capability
- Cool color temperature near 5000 K
Correct answer: High efficacy and long lamp life
HPS lamps deliver 80-150 lm/W efficacy and lifespans of 24,000+ hours, making them cost-effective for outdoor and industrial applications despite poor CRI.
CEM Lighting Systems and Controls 2
What is lumen depreciation?