CLD Sustainable & Energy-Efficient Lighting Solutions 2 — Questions and Answers
Question 1: Which lighting control strategy delivers the greatest energy savings in open-plan offices with variable occupancy?
- Scheduled on/off timers
- Daylight harvesting combined with occupancy sensing (Correct answer)
- Manual dimmer switches at each workstation
- High-frequency ballasts with fixed output
Correct answer: Daylight harvesting combined with occupancy sensing
Combining daylight harvesting with occupancy sensing addresses both unoccupied periods and available natural light, maximizing energy reduction.
Question 2: What does the term 'luminous efficacy' measure?
- Lumens output per watt of electrical power consumed (Correct answer)
- Color rendering index relative to a blackbody radiator
- The ratio of useful lumens to total lumens produced
- Foot-candles delivered at the task plane per fixture
Correct answer: Lumens output per watt of electrical power consumed
Luminous efficacy is expressed in lumens per watt (lm/W) and quantifies how efficiently a light source converts electrical energy into visible light.
Question 3: A CLD specifies LED luminaires with an L70 rating of 50,000 hours. What does this mean?
- The fixture will fail completely after 50,000 hours
- Lumen output will drop to 70% of initial output at 50,000 hours (Correct answer)
- The fixture uses 70% less energy than HID after 50,000 hours
- Color temperature shifts by 70K over 50,000 hours
Correct answer: Lumen output will drop to 70% of initial output at 50,000 hours
L70 is an industry-standard LED lumen maintenance metric indicating the point at which output depreciates to 70% of rated initial lumens.
Question 4: Which standard provides the primary energy use intensity (EUI) benchmarks for commercial lighting in US buildings?
- ANSI/IES RP-1
- ASHRAE 90.1 (Correct answer)
- NFPA 101
- IES LM-79
Correct answer: ASHRAE 90.1
ASHRAE 90.1 sets mandatory lighting power density (LPD) limits and controls requirements for commercial buildings in the US.
Question 5: In the context of sustainable design, what is the primary benefit of specifying fixtures with a high Optical System Efficiency (OSE)?
- Higher correlated color temperature output
- More lumens delivered to the task with less lamp wattage (Correct answer)
- Reduced lamp replacement frequency
- Improved thermal management of the LED driver
Correct answer: More lumens delivered to the task with less lamp wattage
High OSE means the optic wastes fewer lumens, so a lower-wattage source can meet the same illuminance target, reducing energy consumption.
Question 6: A lighting designer is evaluating two LED products: Product A is 130 lm/W and Product B is 110 lm/W. Both meet the photometric requirement. Which factor should most influence the sustainable choice?
- Product A, solely based on higher lm/W
- Product B if it carries a longer warranty and better lumen maintenance data (Correct answer)
- Product A only if it has a higher CRI
- Product B if it is manufactured domestically
Correct answer: Product B if it carries a longer warranty and better lumen maintenance data
A longer warranty and verified lumen maintenance (L70/L80 data) indicate real-world energy and replacement savings that can outweigh a modest efficacy gap.
Question 7: Which metric is used to quantify the light pollution impact of an outdoor luminaire on the night sky?
- Backlight-Uplight-Glare (BUG) rating (Correct answer)
- Color Rendering Index (CRI)
- Unified Glare Rating (UGR)
- Photopic-to-Scotopic (P/S) ratio
Correct answer: Backlight-Uplight-Glare (BUG) rating
The BUG rating classifies a luminaire's backlight, uplight, and glare distribution, with uplight being the component most directly linked to sky glow.
CLD Sustainable & Energy-Efficient Lighting Solutions 2
Which lighting control strategy delivers the greatest energy savings in open-plan offices with variable occupancy?