CLD Controls and Dimming 5 — Questions and Answers
Question 1: What is a 'tunable white' lighting system, and which control parameter does it add beyond dimming?
- A system that dims to a warm white only, controlled by a single 0-10V signal
- A system that adjusts both intensity and correlated color temperature (CCT) using separate or combined control channels (Correct answer)
- A system that changes hue across the full RGB spectrum
- A system with fixed CCT that uses dimming to simulate color change
Correct answer: A system that adjusts both intensity and correlated color temperature (CCT) using separate or combined control channels
Tunable white systems independently control intensity and CCT—often via two channels or a specialized protocol—allowing the designer to adjust both how bright and how warm or cool the light appears.
Question 2: In a DALI system, what is a 'group' and how does it differ from an 'address'?
- A group is a single fixture's unique identifier; an address is a collection of fixtures
- A group assigns multiple DALI devices to respond together to a single command, while an address targets one individual device (Correct answer)
- Groups are used only for emergency lighting; addresses are for general lighting
- Groups require a separate DALI power supply; addresses do not
Correct answer: A group assigns multiple DALI devices to respond together to a single command, while an address targets one individual device
DALI allows up to 16 groups per segment; a group command dims all member devices simultaneously, while an individual address command targets only one of the 64 possible devices.
Question 3: An occupancy sensor fails to turn off lights after occupants leave. Which sensor setting should the designer adjust first?
- Sensitivity (detection range)
- Time delay (hold time) (Correct answer)
- Dimming ramp rate
- Load wattage rating
Correct answer: Time delay (hold time)
The time delay (or hold time) setting determines how long the sensor waits after the last detected motion before switching off the lights; increasing it causes lights to stay on longer.
Question 4: What is the function of a 'vacancy sensor' as opposed to a standard 'occupancy sensor'?
- A vacancy sensor dims lights automatically; an occupancy sensor only switches them off
- A vacancy sensor requires manual activation to turn lights on but turns them off automatically when the space is vacant (Correct answer)
- A vacancy sensor uses ultrasonic technology; an occupancy sensor uses passive infrared
- A vacancy sensor is required only in restrooms under energy codes
Correct answer: A vacancy sensor requires manual activation to turn lights on but turns them off automatically when the space is vacant
A vacancy sensor (manual-on/auto-off) requires a person to manually turn on lights but switches them off automatically after vacancy, offering more energy savings and user control than auto-on occupancy sensors.
Question 5: Which energy code provision requires lighting controls to allow occupants to reduce lighting power by at least 50% in open office areas?
- Automatic daylighting control
- Occupant override (bi-level switching or dimming) (Correct answer)
- Demand response load shed
- Emergency egress lighting requirement
Correct answer: Occupant override (bi-level switching or dimming)
ASHRAE 90.1 and IECC require occupant-accessible controls (bi-level switching, dimming, or partial-off switching) that allow at least a 50% reduction in lighting power in open offices and similar spaces.
Question 6: A controls integrator programs a 'ramp-to-off' fade instead of an instant switch-off. What is the human-factors justification for this approach?
- It reduces harmonic distortion on the electrical system
- A gradual fade warns occupants that lights are about to turn off, avoiding sudden darkness that causes disorientation (Correct answer)
- It extends LED driver lifetime by reducing thermal cycling
- It satisfies code requirements for emergency egress lighting
Correct answer: A gradual fade warns occupants that lights are about to turn off, avoiding sudden darkness that causes disorientation
A slow fade to off gives occupants a visual cue that lights will extinguish, allowing them time to respond (e.g., wave to reset the sensor) and avoiding the safety hazard of sudden darkness.
Question 7: When integrating a lighting control system with a building's circadian or human-centric lighting strategy, which parameter is most important to schedule throughout the day?
- Fixture lumen output depreciation rate
- Correlated color temperature (CCT) in addition to illuminance level (Correct answer)
- Dimmer curve shape (linear vs. logarithmic)
- Number of DMX universes allocated
Correct answer: Correlated color temperature (CCT) in addition to illuminance level
Circadian (human-centric) lighting strategies adjust CCT—warmer in morning/evening, cooler at midday—alongside illuminance levels to support the body's natural circadian rhythm.
CLD Controls and Dimming 5
What is a 'tunable white' lighting system, and which control parameter does it add beyond dimming?