CLD Electrical Systems & Lighting Control 5 — Questions and Answers
Question 1: A lighting designer is coordinating with an electrical engineer on harmonic distortion. Which type of luminaire driver is most likely to introduce significant harmonics into the distribution system?
- Magnetic ballast with power factor correction capacitor
- High-quality LED driver with active power factor correction (PFC)
- LED driver with no PFC and high total harmonic distortion (THD) (Correct answer)
- Incandescent lamp on a resistive circuit
Correct answer: LED driver with no PFC and high total harmonic distortion (THD)
LED drivers without active PFC can exhibit high THD (>20%), injecting harmonic currents that overheat neutrals and transformers in a distribution system.
Question 2: Which ASHRAE 90.1 control requirement mandates automatic shutoff of lighting in most commercial spaces?
- Daylighting controls in all perimeter zones
- Occupant sensor or time-of-day schedule shutoff for interior spaces (Correct answer)
- Demand response interface at the main panel
- Manual-on switching for all exterior luminaires
Correct answer: Occupant sensor or time-of-day schedule shutoff for interior spaces
ASHRAE 90.1 requires automatic shutoff controls (occupancy sensors or scheduling) for interior lighting in most commercial occupancy types.
Question 3: In a DMX512 lighting control system, what is the maximum number of individual channels (slots) addressable on one universe?
- 128
- 256
- 512 (Correct answer)
- 1024
Correct answer: 512
A single DMX512 universe carries exactly 512 channels (slots), each carrying an 8-bit value from 0–255.
Question 4: A lighting control specification calls for 'bi-level switching' in a warehouse. What does this control strategy accomplish?
- It switches the space between full ON and full OFF only
- It allows the space to operate at two preset levels (e.g., 100% occupied, 30% unoccupied) rather than just on or off (Correct answer)
- It independently controls warm and cool LED channels
- It divides the space into two separately switched circuits
Correct answer: It allows the space to operate at two preset levels (e.g., 100% occupied, 30% unoccupied) rather than just on or off
Bi-level switching provides two pre-set light levels — typically full output when occupied and a reduced level during low-occupancy periods — satisfying energy codes with a simple relay-based approach.
Question 5: What is the purpose of a 'neutral conductor' in a modern electronic dimmer installation?
- It provides the ground fault return path only
- It supplies the low-voltage power needed by the dimmer's electronics without drawing it through the load (Correct answer)
- It carries the dimming signal to the driver
- It is not required for electronic dimmers
Correct answer: It supplies the low-voltage power needed by the dimmer's electronics without drawing it through the load
Modern electronic dimmers require a neutral to power their internal circuitry, preventing flicker or buzzing that occurs when the dimmer steals power through the load at low dim levels.
Question 6: A photosensor used for daylighting control is described as 'closed-loop.' What does this mean operationally?
- The sensor measures only daylight without regard to electric light contribution
- The sensor measures the combined daylight and electric light at the workplane and adjusts electric light to maintain a target illuminance (Correct answer)
- The sensor shuts off all electric light when daylight exceeds a threshold
- The sensor only responds to changes in outdoor illuminance levels
Correct answer: The sensor measures the combined daylight and electric light at the workplane and adjusts electric light to maintain a target illuminance
A closed-loop photosensor measures total light at the work surface (daylight + electric) and continuously dims or brightens electric lighting to maintain a set point regardless of external conditions.
Question 7: Which NEC article governs the installation of lighting track and specifies that it must not be used in certain hazardous locations or where subject to physical damage?
- Article 410 (Correct answer)
- Article 490
- Article 517
- Article 600
Correct answer: Article 410
NEC Article 410 covers luminaires, lampholders, and lighting track, including prohibitions on track use in wet or damp locations, hazardous locations, and areas subject to physical damage.
CLD Electrical Systems & Lighting Control 5
A lighting designer is coordinating with an electrical engineer on harmonic distortion.
Which type of luminaire driver is most likely to introduce significant harmonics into the distribution system?