CLD Luminaire Selection 5 — Questions and Answers
Question 1: A CLD is designing lighting for a library reading room with skylights. Which luminaire selection strategy best supports daylight integration?
- Fixed output high-wattage downlights at maximum lumen output
- Continuously dimmable luminaires compatible with daylight harvesting controls (Correct answer)
- Non-dimmable energy-efficient LED troffers
- High-color-temperature fluorescent for visual similarity to daylight
Correct answer: Continuously dimmable luminaires compatible with daylight harvesting controls
Continuously dimmable luminaires allow daylight harvesting systems to reduce electric light output proportionally as daylight levels increase, saving energy and maintaining consistent illuminance.
Question 2: For a stairwell egress lighting application under NFPA 101, which luminaire placement strategy meets average illuminance requirements on the tread surfaces?
- Ceiling-mounted luminaires only at the top landing
- Wall-mounted luminaires at intermediate landing heights positioned to illuminate treads (Correct answer)
- Luminaires mounted solely at the bottom of the stair run
- Skylights as the primary stair illumination source
Correct answer: Wall-mounted luminaires at intermediate landing heights positioned to illuminate treads
Wall-mounted luminaires at intermediate heights provide direct illumination on tread surfaces at angles that reveal step edges, meeting life-safety code requirements.
Question 3: A restaurant designer wants to create a candlelight effect using electric lighting. Which combination of luminaire characteristics best achieves this?
- High-CRI 5000K downlights at full brightness
- Low-lumen 1800K–2200K sources with warm-dim capability (Correct answer)
- Wide-distribution 3000K wall sconces at maximum output
- Tunable white luminaires set to 6500K for high contrast
Correct answer: Low-lumen 1800K–2200K sources with warm-dim capability
Warm-dim LED sources that shift toward amber at lower dim levels (1800K–2200K) closely replicate the spectral quality and ambiance of candlelight.
Question 4: A luminaire manufacturer's data lists a System Efficacy of 120 lm/W. How does this differ from LED chip efficacy?
- System efficacy includes driver losses, thermal losses, and optical losses; chip efficacy does not (Correct answer)
- System efficacy is always higher than chip efficacy
- System efficacy measures only the LED package output
- System efficacy excludes the driver power consumption
Correct answer: System efficacy includes driver losses, thermal losses, and optical losses; chip efficacy does not
System (luminaire) efficacy accounts for all losses including the LED driver, thermal derating, and optical elements, giving a real-world lm/W figure lower than bare LED chip efficacy.
Question 5: Which luminaire characteristic is most critical when specifying fixtures for a clean room environment (ISO Class 5) in a pharmaceutical facility?
- High CRI (>90) for color accuracy
- Smooth, non-particulate-trapping surfaces and sealed housing (Correct answer)
- Narrow beam distribution for task lighting
- Warm color temperature for worker comfort
Correct answer: Smooth, non-particulate-trapping surfaces and sealed housing
Clean room luminaires must have smooth, flush, sealed housings that prevent particulate accumulation and can withstand chemical cleaning agents without contaminating the environment.
Question 6: A designer is comparing two LED luminaires: Luminaire A has a higher initial lumen output but lower L70 rating, while Luminaire B has slightly lower initial lumens but an L70 of 100,000 hours. For a 24/7 commercial application, which is the better specification choice and why?
- Luminaire A; initial brightness is most important for customer perception
- Luminaire B; longer lumen maintenance reduces relamping costs over the installation life (Correct answer)
- Luminaire A; shorter life means newer technology sooner
- Luminaire B; lower initial output always indicates better quality
Correct answer: Luminaire B; longer lumen maintenance reduces relamping costs over the installation life
In 24/7 applications, longer lumen maintenance (L70 at 100,000 hours) significantly reduces maintenance labor and replacement costs, providing lower lifecycle cost despite slightly lower initial output.
Question 7: A CLD specifies luminaires with a minimum Scotopic/Photopic (S/P) ratio consideration for a roadway application. What is the primary benefit of selecting luminaires with a higher S/P ratio at mesopic light levels?
- Higher lumen output per fixture
- Improved perceived brightness and visibility at night with lower photopic lumens (Correct answer)
- Better color rendering of vehicle paint colors
- Reduced glare to oncoming drivers
Correct answer: Improved perceived brightness and visibility at night with lower photopic lumens
At mesopic (twilight/low-light) levels, the eye's scotopic response contributes to vision; luminaires with higher S/P ratios appear brighter to the dark-adapted eye, enabling lower installed wattage while maintaining perceived visibility.
CLD Luminaire Selection 5
A CLD is designing lighting for a library reading room with skylights.
Which luminaire selection strategy best supports daylight integration?