TRIAC vs ELV vs MLV Dimmers: Which One Does Your LED Need?

If an LED fixture's cut sheet says "TRIAC," "ELV" or "MLV," it is telling you what kind of phase-cut dimmer it expects. A poor match between LED and dimmer can cause flicker, audible buzzing, a limited dimming range, or lights that stay on or flash when they should be off. This guide explains what each term means, how they differ from 0-10V, and how to pick the right dimmer for the fixture you are actually installing.

What phase-cut dimming is

TRIAC, MLV and ELV are all phase-cut dimmers. A phase-cut dimmer does not send a separate control signal to the light. It changes the AC power itself, cutting away part of the sine wave so the fixture receives less voltage. A small cut dims slightly; a bigger cut dims further.

That is the key difference from 0-10V, DALI and DMX, which send the dimming level separately from the power feeding the fixture. Phase-cut dimming was developed for incandescent lamps, and most simple wall-box versions are two-wire devices that replace a standard switch. LEDs draw power very differently from incandescent lamps, which is why they can be picky about which dimmer they are paired with.

TRIAC dimmers (forward phase, leading edge)

A TRIAC dimmer cuts the front of each half-wave, which is why it is also called a forward-phase or leading-edge dimmer. You will also see it labelled INC, for incandescent. All four names describe the same method.

Phase control, originally built for incandescent lamps, is used by most of the installed base of dimming systems. Many LED lamps and fixtures are designed to work on it, but "designed to work on TRIAC" is not the same as "works on every TRIAC dimmer," which is where the compatibility standard below comes in.

MLV dimmers (magnetic low voltage)

An MLV dimmer is also a forward-phase dimmer. It was built for low-voltage lighting that runs on a magnetic (core-and-coil) transformer. What separates it from a plain TRIAC dimmer is extra circuitry to keep it from putting DC current into the transformer, which could overheat the transformer or the dimmer and shorten their life.

Use an MLV dimmer when the fixture or transformer manufacturer calls for MLV, on low-voltage systems fed by a magnetic transformer.

ELV dimmers (reverse phase, trailing edge)

An ELV dimmer cuts the back of each half-wave, so it is a reverse-phase or trailing-edge dimmer. ELV stands for electronic low voltage: these dimmers were originally designed to dim low-voltage halogen lamps running on electronic transformers.

Some LED manufacturers recommend reverse-phase (ELV) dimmers for their products. Compatibility can also change between product generations: PNNL gives the example of an older LED that may work well with only a few ELV dimmers, while its newer model works with more forward-phase dimmers but no longer works well with ELV. Start with the fixture's current documentation, and confirm with a mockup, especially when the manufacturer gives little firm guidance. If the cut sheet says ELV or reverse phase, use an ELV dimmer or a dimmer set to reverse-phase mode.

TRIAC vs ELV vs MLV at a glance

	TRIAC (INC)	MLV	ELV
Phase cut	Forward (leading edge)	Forward (leading edge)	Reverse (trailing edge)
Originally built for	Incandescent / halogen	Low-voltage lighting on magnetic transformers	Low-voltage halogen on electronic transformers
Extra feature	—	Circuitry to prevent DC current into the transformer	—
Separate control wires?	No	No	No

Is ELV the same as 0-10V?

No. ELV is a phase-cut method: it dims by trimming the line-voltage power going to the fixture. 0-10V leaves the power alone and sends the dimming level over separate control wires to a 0-10V driver. The two are generally not interchangeable: a 0-10V driver needs a 0-10V control, and a phase-dimmable fixture needs a compatible phase-cut dimmer. Our guide to what 0-10V dimming is covers the 0-10V side, including current sinking vs sourcing.

Phase-selectable and "adaptive" dimmers

Many basic wall-box dimmers control one load type. Larger multi-scene and architectural systems may let you set the load type in the field, and some can sense the connected load and switch to the most suitable mode on their own. Lutron's compliance list, for example, includes phase-selectable and phase-adaptive models that are marked compliant with the NEMA standard "when set to forward-phase mode." If you are using one of these, the load-type setting is part of the install, not an afterthought.

Two-wire vs neutral-wire dimmers

A basic dimmer connects only to the line and the load, in series with the lights, with no neutral. That makes it harder for the dimmer to power its own electronics. LED loads can make it worse: some do not pass enough current when off to keep a two-wire dimmer working, and others accept a little current when off and respond with strobing or "ghosting" (a faint glow when the light should be off). Newer dimmers and LED sources have largely addressed this. A dimmer with a neutral connection largely avoids it, and PNNL recommends bringing a neutral to every wall box on new and major remodel work. If you are working in an older box without a neutral, see do smart switches need a neutral wire.

NEMA SSL 7A: the compatibility standard, and its limits

NEMA SSL 7A, Phase-Cut Dimming for Solid State Lighting, sets basic compatibility requirements for pairing a forward-phase dimmer with dimmable LED light engines, both screw-in lamps and fixtures with separate drivers. Per Leviton's compliance note, it does not apply to reverse-phase ELV or 0-10V dimmers. PNNL's 2013 description of the standard adds that its LED light engines exclude low-voltage sources that do not connect directly to AC mains, although a low-voltage source together with its step-down transformer may count as one. Look for "SSL 7A" on the dimmer or its packaging.

Cautions from the sources:

• SSL 7A defines only basic dimming criteria. Lutron still points users to its own lamp-by-lamp compatibility testing.
• Compliance is about basic compatibility between compliant products, not guaranteed dimming quality. It does not predict how a compliant dimmer behaves with older, non-compliant LEDs.
• Compliance can depend on settings: Leviton's listed dimmers are compliant in their factory default state, and changing the minimum-level adjustment on certain models may make them non-compliant. Lutron lists several phase-selectable and phase-adaptive dimmers as compliant only when set to forward-phase mode.

How to choose the right dimmer

1. Start with the fixture, not the dimmer. Check the LED lamp or fixture manufacturer's current spec sheet for the recommended dimmer type (for phase-cut: INC/TRIAC, MLV or ELV) and any stated limits, such as a minimum dim level, then check the dimmer manufacturer for a report on that dimmer with that LED product. Treat manufacturer claims as potential performance: actual results often depend on the specific dimmer make and model.
2. For low-voltage fixtures, identify the transformer. MLV dimmers were built for magnetic transformers and ELV dimmers for electronic ones, so note which type the fixture uses. Then follow the transformer or fixture manufacturer's stated dimmer type.
3. Respect the LED load rating, not the incandescent rating. LED-specific maximum ratings are typically lower than incandescent ratings; PNNL notes that some wall-box dimmers have been derated 3 to 4 times, for example 600W for incandescent and 150W for LED. Use the dimmer manufacturer's LED rating, or the dimmer or lamp manufacturer's maximum number of lamps per dimmer. If no such guidance exists, PNNL says a specifier may consider derating a line-voltage (INC) dimmer by 5 to 10 times, for example treating a 600W dimmer as 60 to 120W, or, when no precise value is available, a conservative factor of 10 (or choosing other products). That fallback does not cover MLV or ELV dimmers.
4. Do not mix forward-phase and reverse-phase LED products on one zone. They will not dim alike, and PNNL notes a small possibility of eventual LED, driver or dimmer failure.
5. Mock it up. PNNL ranks a full mockup as its highest-confidence check, and says mockups are often essential when manufacturers give little firm guidance. Test the actual dimmer with enough of the actual fixtures to simulate the minimum and maximum load on a circuit, and run the full dimming range. If the behavior is unacceptable and the dimmer offers another load type (such as ELV), switch and test again.

If you are chasing flicker or buzz on an existing install, our guide to LED flicker and dimmer buzz walks through the usual causes. For Lutron specifically, compare Caséta vs Maestro and Sunnata vs Maestro.

Shop dimmers at Rock

Rock Lighting & Electric stocks MLV, ELV, phase-selectable and 0-10V dimmers from brands including Lutron and Eaton. Browse our dimmers collection, or send us your fixture schedule and we will match each fixture to a compatible dimmer before you order.

Frequently asked questions

What is the difference between TRIAC and ELV dimming? Both are phase-cut dimmers. A TRIAC dimmer cuts the leading edge of the AC wave (forward phase), and an ELV dimmer cuts the trailing edge (reverse phase). ELV dimmers were originally built for low-voltage halogen on electronic transformers. Start with the LED manufacturer's recommended dimmer type, and confirm with a mockup, especially when the manufacturer gives little firm guidance.

Is an MLV dimmer the same as a TRIAC dimmer? Both are forward-phase dimmers, but an MLV dimmer adds circuitry to keep DC current out of a magnetic transformer, which could otherwise overheat the transformer or the dimmer. Use MLV when the fixture or transformer manufacturer calls for it.

Is ELV dimming the same as 0-10V? No. ELV dims by trimming the line-voltage power to the fixture. 0-10V leaves the power alone and sends the dimming level over separate control wires to a 0-10V driver. A 0-10V driver needs a 0-10V control, not an ELV dimmer.

Does NEMA SSL 7A cover ELV dimmers? No. According to Leviton's compliance note, NEMA SSL 7A covers forward-phase dimmers paired with dimmable LED light engines, and does not apply to reverse-phase ELV or 0-10V dimmers.

How much LED load can I put on a dimmer? Use the dimmer manufacturer's LED rating (typically lower than its incandescent rating), or the dimmer or lamp manufacturer's maximum lamp count. If no LED guidance exists, a 2013 DOE/PNNL report says a specifier may consider derating a line-voltage (INC) dimmer by 5 to 10 times, for example treating a 600W dimmer as 60 to 120W, or, when no precise value is available, a conservative factor of 10 (or choosing other products). That fallback does not cover MLV or ELV dimmers.

Can I put TRIAC and ELV fixtures on the same dimmer? It is best not to. Forward-phase and reverse-phase LED products will not dim the same way on one zone, and PNNL notes a small possibility of eventual LED, driver or dimmer failure. Keep them on separate zones, each with the dimmer type its fixtures call for.

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