CLD Sustainable & Energy-Efficient Lighting Solutions 4 — Questions and Answers
Question 1: Which color temperature range (CCT) is generally recommended for outdoor street lighting to minimize impact on wildlife and nocturnal ecosystems?
- 6500K (cool white)
- 5000K (neutral white)
- 4000K (neutral white)
- Below 3000K (warm white or amber) (Correct answer)
Correct answer: Below 3000K (warm white or amber)
Warm-white or amber LEDs (≤3000K, ideally narrowband amber) emit less short-wavelength blue light, which is most disruptive to circadian rhythms of wildlife and humans.
Question 2: What does 'lighting power density' (LPD) express, and how is it used in energy compliance?
- Total lumens per square foot; compared against IES footcandle tables
- Installed watts per square foot; compared against ASHRAE 90.1 allowances (Correct answer)
- Lamp efficacy in lm/W; compared against DOE minimum standards
- Fixture spacing-to-mounting-height ratio; used in uniformity calculations
Correct answer: Installed watts per square foot; compared against ASHRAE 90.1 allowances
LPD (W/ft²) measures installed lighting wattage relative to floor area and must not exceed ASHRAE 90.1 space-by-space or whole-building allowances for energy code compliance.
Question 3: A CLD proposes replacing 400W metal halide high-bay fixtures with LED high-bays in a warehouse. Which calculation confirms the energy savings are real and not offset by overlighting?
- Verify the new LPD is below code maximum and illuminance levels match the IES RP target (Correct answer)
- Confirm the LED CCT matches the original metal halide CCT
- Calculate that total lumen output of new fixtures exceeds the original system
- Ensure the LED fixtures have the same beam angle as the metal halide reflectors
Correct answer: Verify the new LPD is below code maximum and illuminance levels match the IES RP target
Comparing the new LPD to code limits and the resulting illuminance to IES recommended levels confirms energy reduction without sacrificing or exceeding the required light levels.
Question 4: In sustainable lighting design, 'adaptive lighting' in a smart city context most commonly refers to:
- Automatically adjusting street light levels based on real-time traffic, pedestrian presence, or time of night (Correct answer)
- Changing fixture color temperature with the seasons
- Replacing fixtures on a fixed schedule regardless of actual condition
- Using manual dimmer controls operated by city maintenance staff
Correct answer: Automatically adjusting street light levels based on real-time traffic, pedestrian presence, or time of night
Adaptive street lighting uses sensors or networked control to dim or brighten luminaires in response to actual activity, reducing energy use during low-traffic periods.
Question 5: What is the purpose of an 'occupancy sensor dead band' setting in an energy-efficient lighting control system?
- A time delay before lights turn off after the last detected motion, preventing nuisance switching (Correct answer)
- The minimum wattage the dimmer can reach before switching off
- A zone around the sensor where detection is intentionally disabled
- The frequency range filtered from the sensor to avoid false triggers from HVAC
Correct answer: A time delay before lights turn off after the last detected motion, preventing nuisance switching
The time-delay (dead band) after last detection prevents lights from cycling off and on rapidly when occupants are briefly still, balancing comfort and energy savings.
Question 6: Which certification program specifically evaluates and labels LED luminaires for energy performance, with data verified by accredited labs?
- ENERGY STAR for Luminaires
- DLC (DesignLights Consortium) Qualified Products List
- UL 1598 listing
- Both A and B, as they serve different market segments (Correct answer)
Correct answer: Both A and B, as they serve different market segments
ENERGY STAR targets residential and light commercial fixtures while the DLC QPL focuses on commercial and industrial products; both require third-party lab testing for listed efficacy and performance claims.
Question 7: A retail store uses track lighting set to 100% output. A sensor-based system is proposed to dim fixtures to 60% during low-traffic hours. Approximately what percentage of lighting energy is saved during those hours?
- 10%
- 25%
- 40% (Correct answer)
- 60%
Correct answer: 40%
Dimming LED drivers to 60% of full output typically reduces power consumption by approximately 40%, since LED systems reduce wattage nearly proportionally to output level.
CLD Sustainable & Energy-Efficient Lighting Solutions 4
Which color temperature range (CCT) is generally recommended for outdoor street lighting to minimize impact on wildlife and nocturnal ecosystems?