CLD Controls and Dimming 2 — Questions and Answers
Question 1: Which dimming protocol uses a two-wire digital bus to individually address up to 64 devices per segment?
- DMX512
- DALI (Correct answer)
- 0-10V analog
- Phase-cut dimming
Correct answer: DALI
DALI (Digital Addressable Lighting Interface) supports up to 64 individually addressable devices on a single two-wire bus segment.
Question 2: Forward-phase (leading-edge) dimming is best suited for which type of load?
- Electronic LED drivers
- Magnetic low-voltage transformers (Correct answer)
- Capacitive loads
- DALI-controlled fixtures
Correct answer: Magnetic low-voltage transformers
Forward-phase (leading-edge) dimming was designed for magnetic low-voltage transformers and resistive loads, not electronic or capacitive loads.
Question 3: In a 0-10V dimming system, what light output does a 0V control signal typically produce?
- Full output (100%)
- Minimum dimmed output (≈1-10%) (Correct answer)
- The fixture turns completely off
- 50% output
Correct answer: Minimum dimmed output (≈1-10%)
A 0V signal in a 0-10V system drives the fixture to its minimum dim level, not completely off; a separate switch is needed to cut power.
Question 4: What is the primary advantage of reverse-phase (trailing-edge) dimming over forward-phase dimming for LED loads?
- Higher maximum wattage capacity
- Softer turn-on reduces inrush current and audible noise (Correct answer)
- Eliminates the need for a neutral wire
- Supports wireless communication
Correct answer: Softer turn-on reduces inrush current and audible noise
Reverse-phase (trailing-edge) dimming cuts power at the end of each half-cycle, reducing inrush current and minimizing audible buzz common with LED and electronic drivers.
Question 5: A lighting designer specifies a scene-based control system. Which feature distinguishes a 'scene' from a simple on/off switch?
- Scenes require wired connections only
- Scenes store preset level combinations for multiple zones simultaneously (Correct answer)
- Scenes can only control incandescent sources
- Scenes bypass dimmer electronics
Correct answer: Scenes store preset level combinations for multiple zones simultaneously
A scene stores and recalls preset dimming levels for multiple zones at once, allowing complex lighting environments to be activated with a single button press.
Question 6: When installing dimmers on a shared neutral (multi-wire branch circuit), what critical issue can arise?
- Voltage drop on the hot conductors
- Neutral conductor overload due to additive harmonic currents (Correct answer)
- Reduced dimming range on all fixtures
- Ground fault circuit interruption
Correct answer: Neutral conductor overload due to additive harmonic currents
On multi-wire branch circuits, harmonics from multiple phase-cut dimmers can add on the shared neutral rather than cancel, potentially overloading it.
Question 7: Which dimming curve provides a perceptually linear change in apparent brightness as the control signal changes linearly?
- Linear (arithmetic) curve
- Square-law (logarithmic) curve (Correct answer)
- Stepped curve
- Sine-wave curve
Correct answer: Square-law (logarithmic) curve
A square-law or logarithmic dimming curve compensates for the eye's non-linear sensitivity, making equal control-signal steps appear as equal steps in perceived brightness.
CLD Controls and Dimming 2
Which dimming protocol uses a two-wire digital bus to individually address up to 64 devices per segment?