CLD Interior Lighting 5 — Questions and Answers
Question 1: A specifier notes that a LED driver has a Power Factor (PF) of 0.55. What is the primary concern with this specification?
- The driver will produce excessive heat
- The driver draws more apparent power from the electrical system than real power, increasing utility demand charges (Correct answer)
- The lamp will flicker noticeably at 60 Hz
- The color temperature will shift over time
Correct answer: The driver draws more apparent power from the electrical system than real power, increasing utility demand charges
A low power factor means the driver draws significant reactive power from the grid, increasing apparent power (kVA) demand and potentially raising utility costs and requiring larger electrical infrastructure.
Question 2: In stairwell and egress lighting design per NFPA 101 Life Safety Code, the minimum average illuminance at the tread surface during normal operation is:
- 1 fc (10 lux) (Correct answer)
- 10 fc (100 lux)
- 5 fc (50 lux)
- 0.5 fc (5 lux)
Correct answer: 1 fc (10 lux)
NFPA 101 requires a minimum of 1 fc (10 lux) at the walking surface along egress paths during normal occupied use.
Question 3: A designer is selecting a luminaire for a space with a very low ceiling (8 ft) and wants to avoid hot spots. Which aperture size is preferable for a recessed downlight?
- 2-inch aperture
- 4-inch aperture
- 6-inch aperture (Correct answer)
- 8-inch aperture
Correct answer: 6-inch aperture
In low-ceiling spaces, a larger aperture (6-inch) distributes light more broadly with lower peak luminance at the aperture, reducing perceptible bright spots and glare at close viewing angles.
Question 4: The term 'efficacy' as applied to a luminaire (system efficacy) is expressed as:
- Lumens per watt (lm/W) of the complete luminaire system including driver (Correct answer)
- Candelas per square meter of the fixture aperture
- Watts per square foot of the illuminated space
- Color rendering index divided by correlated color temperature
Correct answer: Lumens per watt (lm/W) of the complete luminaire system including driver
System efficacy (lm/W) is the total luminous flux delivered by the luminaire divided by the total input power consumed by the complete system, including the driver.
Question 5: In a high-end residential kitchen, a designer wants to prevent shadows on the countertop work surface from overhead cabinet doors. The best solution is to:
- Increase the wattage of the ceiling recessed downlights
- Install under-cabinet task lighting beneath the overhead cabinets (Correct answer)
- Use a single large pendant over the island only
- Switch to a cooler CCT of 5000K for better visibility
Correct answer: Install under-cabinet task lighting beneath the overhead cabinets
Under-cabinet lighting positioned beneath overhead cabinets illuminates the countertop directly, eliminating shadow cast by cabinets that overhead fixtures would otherwise cause.
Question 6: What is the recommended maintained illuminance level for a general open-plan office task area per IESNA RP-1?
- 10 fc (100 lux)
- 30 fc (300 lux) (Correct answer)
- 100 fc (1,000 lux)
- 5 fc (50 lux)
Correct answer: 30 fc (300 lux)
IESNA RP-1 recommends approximately 30 fc (300 lux) as the maintained average illuminance for general office tasks on the horizontal work plane.
Question 7: Which of the following describes the primary function of a 'ballast factor' (BF) when applied to fluorescent luminaires still in service?
- It adjusts the fixture's color rendering index based on ambient temperature
- It is a multiplier expressing actual lamp lumen output relative to rated output when used with a specific ballast (Correct answer)
- It measures the ratio of UV to visible light output
- It quantifies flicker percentage at line frequency
Correct answer: It is a multiplier expressing actual lamp lumen output relative to rated output when used with a specific ballast
Ballast factor is the ratio of the lamp's actual lumen output when operated on a specific ballast to its rated output on a standard reference ballast, used to adjust photometric calculations.
CLD Interior Lighting 5
A specifier notes that a LED driver has a Power Factor (PF) of 0.55.
What is the primary concern with this specification?