Guide to Dimming Low-Voltage Lighting

Overview

This guide addresses common questions for Lutron Technical Assistance and Applications personnel regarding low-voltage dimming applications. Lutron offers low-voltage dimmers for fixtures using magnetic transformers. For electronic (solid-state) transformer-supplied low-voltage lighting, Lutron has developed specialized dimming circuitry, integrated into a series of dimmers for electronic low-voltage (ELV) transformer loads. Lutron provides dimmers for both magnetic and electronic transformer types across various product families.

Facts About Low-Voltage Lighting

Why Use Low-Voltage Lighting?

• Provides excellent illumination for precise, concentrated beams.
• Contributes to extended lamp life and increased safety.
• Small fixture sizes allow easy aiming and reconfiguration.
• Common applications include residences, display lighting, task lighting, and product highlighting.

What is Low-Voltage Lighting?

Low-voltage lighting uses a transformer to reduce standard 120 V~ line voltage to 12 V~ or 24 V~, powering incandescent low-voltage lamps. Examples include AR111, MR16, MR11, PAR36, T3-1/4, T5, and striplites. Many of these lamps are tungsten halogen.

Where is the Transformer Located?

Transformers can be mounted remotely or integrated into the fixture.

Does Dimming Affect Lamp Life?

Dimming generally increases the life expectancy of low-voltage lamps. If a low-voltage halogen lamp darkens, turning it on at 100% illumination for 10 minutes can eliminate the black residue caused by tungsten evaporation.

Dimming Low-Voltage Lighting

Dimming a low-voltage fixture involves the dimmer controlling the 120 V~ line voltage input to the transformer. Two main types of transformers are used:

• Magnetic (core and coil) low-voltage (MLV)
• Electronic (solid-state) low-voltage (ELV)

Important: It is crucial to identify the transformer type in the lighting fixture before selecting a dimmer, as their characteristics require different dimming considerations. Consult the fixture manufacturer's literature if unsure.

Note: Line voltage incandescent and low-voltage fixtures can share a circuit, provided the correct low-voltage dimmer is used and the total load does not exceed the dimmer's capacity. Magnetic and electronic transformers should not be mixed on the same dimming circuit. Some low-voltage fixtures are not dimmable; check manufacturer literature.

Differences Between Magnetic and Electronic Transformers

Magnetic Transformers

Magnetic transformers step down 120 V~ to 12 V~ or 24 V~ using a copper wound steel core, making them inductive. They are typically large and heavy, available in toroidal or laminated EI core construction. Lutron MLV dimmers are recommended for these. Products are rated in volt-ampere (VA). A primary fuse is recommended for overheating protection.

Electronic Transformers

Electronic transformers also step down 120 V~ to 12 V~ or 24 V~, but use electronic circuitry that is capacitive. They are compact and lightweight. Due to higher efficiency, Lutron ELV dimmers are rated in watts (W), corresponding to the connected lamp load.

Differences Between MLV and ELV Dimmers

MLV dimmers use standard phase control ("leading edge"), while ELV dimmers use reverse phase control ("trailing edge"). Standard phase control is suitable for inductive (MLV, fans) and resistive (incandescent) loads. Reverse phase control is for capacitive (ELV) and resistive loads.

Standard Phase Control ("Leading Edge")

With standard phase control, the dimmer delays power delivery into the line cycle. Power is supplied until the zero cross. Dimming is achieved by adjusting the delay at which the dimmer begins conducting.

Reverse Phase Control ("Trailing Edge")

With reverse phase control, the dimmer begins supplying power immediately after the zero cross. Dimming is achieved by adjusting the delay at which the dimmer stops conducting.

[Diagram Description: Two waveform illustrations showing AC voltage cycles. The first, "Standard phase control or 'leading edge'," shows the dimmer starting to conduct partway through the positive and negative cycles, cutting off at the zero crossing. The second, "Reverse phase control or 'trailing edge'," shows the dimmer conducting from the zero crossing until partway through the positive and negative cycles.]

Dimming Magnetic Transformers

Why Use Lutron® MLV Dimmers?

Magnetic transformers are inductive and sensitive to DC voltage, which can cause overheating. Regular incandescent dimmers, which may output small amounts of DC voltage, should not be used as they can damage magnetic transformers. Lutron MLV dimmers are designed to prevent DC voltage application. Compatibility with certain MLV transformers (e.g., those with built-in chokes or "debuzzing coils") may require Lutron microprocessor dimmers with a neutral connection. Standard (non-microprocessor) Diva®, Nova T®, and Skylark® controls are generally compatible. Secondary side protection (PTC, fuses, circuit breakers) is usually compatible, but check with Lutron Technical Support for units with electronic overload/fault detection. MLV dimmers are designed to handle voltage spikes and current surges common with inductive loads.

The VA rating indicates the dimmer's capacity. Wattage ratings are a reference for lamp load, assuming 80% efficiency, to stay within the VA limit.

[Diagram Description: A calculation showing Power to transformer (1000 VA Primary) multiplied by Transformer efficiency (80%) equals Lamp load (800 W Secondary).]

Wiring

Typical wiring for MLV dimmers:

• Diva® Low-Voltage Dimmer: Connects 120 V~ 60 Hz Live (Black wire) and Neutral to the dimmer. The dimmer's output (Black or red wire) connects to the magnetic transformer's primary. The transformer's secondary connects to the lamps.
• Nova® Low-Voltage Dimmer: Similar connections. The Nova® single pole, slide-to-off series requires a neutral wire.

[Diagram Description: Two wiring diagrams for MLV dimmers. The first shows a Diva dimmer connected to a magnetic transformer and lamps. The second shows a Nova dimmer connected to a magnetic transformer and lamps, highlighting the neutral wire requirement for specific Nova models.]

Dimming Electronic Transformers

Why Use Lutron® ELV Dimmers?

Lutron® ELV dimmers are specifically designed for the capacitive characteristics of electronic transformers, which require different dimming considerations. Using MLV or incandescent dimmers with ELV transformers can cause issues like dimmer/fixture buzz, lamp flickering, circuit interaction, and Radio Frequency Interference (RFI), potentially damaging components. Lutron® ELV dimmers use reverse phase control, avoiding the high dV/dT voltage rise associated with standard phase control, which can shorten ELV transformer life and cause acoustic noise. Lutron® ELV dimmers are UL® listed for both ELV and incandescent loads. They can also eliminate AM radio interference on incandescent loads, though they do not affect lamp buzz (refer to Application Note #3 for buzz issues). While some ELV transformers are labeled "dimmable with standard incandescent dimmers," Lutron recommends their ELV dimmers or GRAFIK Eye® systems for optimal performance. Some GRAFIK Eye® systems use standard phase control with an inductor for ELV loads, requiring a neutral connection for accurate zero-cross information. Lutron® ELV dimmers feature overload protection to prevent circuit damage.

Wiring

Typical wiring for ELV dimmers requires a neutral wire:

• Wallbox ELV Dimmer: Connects 120 V~ 60 Hz Live (Black) and Neutral to the dimmer. The dimmer output (Yellow) connects to the electronic transformer's input. The transformer's output connects to the lamps.
• Fluorescent Dimmer with PHPM-WBX-DV-WH: Shows connections for Live, Neutral, Load Neutral, Zone In, Control Neutral, and the dimmer/interface unit to the electronic transformer and lamps.
• GRAFIK Eye® with PHPM-WBX-DV-WH: Similar wiring complexity, showing connections for Live, Neutral, Load Neutral, Zone In, Control Neutral, and the GRAFIK Eye unit/interface to the electronic transformer and lamps.

[Diagram Description: Three wiring diagrams for ELV dimmers. The first is a simple wallbox ELV dimmer. The second shows a fluorescent dimmer with an ELV interface module. The third shows a GRAFIK Eye system with an ELV interface module, all connecting to electronic transformers and lamps.]

Control Options for Low-Voltage Lighting

The following table details Lutron® control options for MLV and ELV low-voltage lighting across various product families and capacities.

Notes:

1. For Hi-Power 2•4•6™ Dimming Module with 600 W incandescent dimmers, use the specified dimmer. For ELV dimming with Hi-Power 2•4•6™, the transformer must be approved for standard incandescent dimmers.
2. Dimming ELV lighting with certain control types requires an ELV interface (e.g., PHPM-WBX-DV-WH) in addition to a fluorescent dimmer. Up to three PHPM-WBX-DV-WH units can connect to a single dimmer, supporting up to 6000 W of ELV load.
3. For loads not listed, contact Lutron Technical Support.
4. To reduce acoustic noise, a Lamp Debuzzing Coil (LDC) may be used with certain products (indicated by *).