Most dimmer callbacks come down to one of three things: the wrong phase-cut type for the LED driver, an undersized or oversized load, or a dimmer that was spec'd for incandescent and pressed into service with LEDs because it was already on the truck. None of those problems is difficult to avoid. They just require the right information before the job goes in, not after the client calls about flickering lights two weeks later. This guide covers how to select, wire, and install a dimmer switch that actually works with LED lighting, from load calculations through to commissioning checks, including two-way configurations.
Why LED Dimming Is Not the Same as Dimming an Incandescent
An incandescent globe is a resistive load. The filament gets hot, it glows, it dims smoothly across the full range of any TRIAC dimmer. LEDs are nothing like that. An LED globe contains a driver circuit that converts 240V AC mains power into the low-voltage DC that the LED chip actually needs. That driver is a reactive, capacitive load, and it responds to phase-cut dimming in ways that an incandescent never would.
The practical consequences show up on the job. A dimmer rated for 600W of incandescent load may be rated for only 150W of LED load, because the driver’s inrush current characteristics are completely different. Some drivers tolerate leading-edge phase cut without complaint. Others buzz, flicker, or fail early when you use the wrong dimmer type. And unlike an incandescent, which is relatively forgiving, a quality LED driver being fed the wrong waveform will tell you about it, usually in front of the client.
This is why dimmer selection for an LED job cannot be treated as a commodity decision. The dimmer and the driver need to be considered as a matched pair, confirmed against each other before anything goes on order.
Phase-Cut Dimming: Leading-Edge, Trailing-Edge, and When Each Applies
Phase-cut dimming works by chopping the AC sine wave. The dimmer lets through only part of each half-cycle, reducing the average power delivered to the fitting. The question is which part of the cycle you cut.
Leading-Edge (TRIAC) Dimmers
TRIAC dimmers fire at the start of each half-cycle, chopping the leading-edge of the waveform. They dominated the Australian residential market for decades because they were cheap, robust, and worked perfectly with resistive incandescent loads. With LED drivers, the picture is more complicated. The abrupt turn-on characteristic of a TRIAC fires into the driver’s input capacitance, which can generate electrical noise, flicker, and buzz from the fitting or transformer. Some LED drivers tolerate it well. Many do not.
Leading-edge dimmers are still appropriate where the specific LED driver has been confirmed compatible, and they remain common in retrofit situations where the existing wiring infrastructure is already built around them. But they should not be the default choice on a fresh LED installation without compatibility testing.
Trailing-Edge (ELV) Dimmers
Trailing-edge dimmers cut the end of the half-cycle instead. The softer turn-on profile is considerably more compatible with the capacitive input stage of most LED drivers. Dimming is smoother across the range, electrical noise is lower, and driver longevity is typically better. For a new LED installation, the trailing-edge is the default recommendation.
The trade-off is that trailing-edge dimmers are generally more expensive than equivalent TRIAC products, and the minimum load threshold can be higher on some models. Check the datasheet before ordering. A trailing-edge dimmer with a 40W minimum LED load on a four-globe circuit of 6W globes is going to give you grief at low levels.
Universal Dimmers
Universal dimmers are designed to detect the load type and adjust their phase-cut behaviour accordingly. In practice, “universal” is a useful starting point but not a guarantee of compatibility. The detection logic works well with mainstream LED drivers from established manufacturers. It can produce unexpected results with budget drivers, unfamiliar imports, or unusual driver configurations. Universal dimmers are not a substitute for compatibility testing on the specific dimmer-driver-globe chain you are actually installing.
Load Calculations Before You Order
Every dimmer has a rated load range: a minimum and a maximum. Both matter for LED installations, and both are worth checking before the order goes in.
The maximum is straightforward: total the LED wattage of all fittings on the circuit and confirm it falls below the dimmer’s rated maximum LED load (not the incandescent maximum, which is a different figure). The minimum is where LED jobs catch people out. An LED circuit with a total load below the dimmer’s minimum rated load will produce unstable dimming behaviour, typically flickering at the bottom of the range, dropout when you push toward 0%, or refusal to turn on at all below a certain level.
A practical example: four GU10 downlights at 7W each give a circuit load of 28W. A dimmer with a minimum LED load of 30W is already borderline. If one globe fails and is temporarily not replaced, you are below the minimum. The professional approach is to specify a dimmer whose minimum load rating is comfortably below the circuit load, with margin to spare.
As a general derating guideline, keep total circuit load below 80% of the dimmer’s rated maximum. On LED circuits, this guards against inrush current peaks during switching and gives the dimmer thermal headroom over a long service life.
Dimmer Switch Wiring: Single Pole, Two-Way, and Intermediate Configurations
Single Pole Wiring
A single-pole dimmer controls one circuit from one location. The dimmer module replaces the existing switch in the backbox. The active conductor from the supply feeds the line terminal; the active conductor going to the fitting feeds the load terminal. Neutral is required by many modern dimmer designs, particularly trailing-edge models. Some two-wire dimmers operate without a neutral by drawing a small parasitic current through the load, but performance with LED drivers is less consistent, and some manufacturers explicitly limit this configuration to specific compatible globes.
If the existing wiring includes a neutral conductor in the switch backbox, use it. It gives you a wider choice of compatible dimmers and produces more stable dimming behaviour across the load range.
Two-Way Dimmer Switch Wiring
A two-way dimming configuration controls a single circuit from two locations: a staircase, a large room with two entry points, or a bedroom where the client wants control from the door and from the bedside. It is a common request and one that trips up the installation when it is not understood properly.
The critical point: you cannot install an active dimmer module at both ends of the circuit. A two-way dimming circuit uses one dimmer module and one compatible slave or remote plate. The dimmer module does all the phase-cut work. The slave plate is a passive control that sends a signal back to the dimmer module, typically via a two-wire signalling connection running between the two backboxes in parallel with the standard two-way traveller loop.
Wiring sequence for a two-way dimmer configuration: the dimmer module is wired at the primary location with supply active to the line, load active to the fitting, and the two traveller conductors connected to the designated signalling terminals. The slave plate at the secondary location connects to the same two traveller conductors. Earth is connected to both backboxes. Neutral at the dimmer backbox if required by the module. No active connections at the slave plate backbox.
Always confirm that the slave plate is from the same manufacturer and designed to be compatible with the specific dimmer module you are using. Mixing brands produces unpredictable signalling behaviour and is one of the more common sources of two-way dimming complaints.
Dimmer Switch and Light Switch on the Same Circuit
Sometimes the brief calls for dimming at one location and a standard on/off switch at another, rather than dimming at both. This is a legitimate configuration, but the term “two-way” is sometimes used loosely to describe it, which confuses.
A standard two-way light switch wired in series with a dimmer module is not a supported configuration for most LED dimmers. The switching action of the standard switch can interrupt the dimmer’s signalling circuit, produce voltage spikes into the driver, or cause the dimmer to behave as if it has lost load. The correct approach is to use a manufacturer-specified slave plate at the secondary location rather than a standard switch, even if the client only wants on/off control at that point. Most slave plates support both full on/off and scene recall, which satisfies the brief without the wiring complications.
Step-by-Step Installation
Important: Under AS/NZS 3000, all fixed-wiring work, including dimmer installation, must be carried out by a licensed electrician. A certificate of compliance is required on completion.
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Isolate the circuit at the switchboard and verify isolation with a voltage tester before touching any conductors. Do not rely on the existing switch being in the off position.
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Remove the existing switch plate and module. Photograph the existing wiring before disturbing any connections.
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Identify the conductors. In a standard single pole configuration: supply active (line), load active to the fitting (load), neutral if present, and earth. In a two-way configuration: supply active, load active, two traveller conductors, neutral if present, and earth.
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Connect conductors to the dimmer module terminals as specified on the module’s wiring diagram. Do not guess terminal assignments. The line/load distinction matters. Reversed connections on some modules will damage the driver or the dimmer.
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Connect the earth to the backbox earth terminal and to the module earth if the module has one.
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Fold conductors carefully into the backbox and seat the module. Do not overtighten fixing screws on plastic-framed modules.
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Restore power and test: switch on, dim up, dim down, check minimum level behaviour. Test across the full circuit with all globes operating. Any flicker, buzz, or instability at this stage is a compatibility or load issue to diagnose before the plate goes on and the walls are closed.
Common problems and how to diagnose them
Most LED dimmer problems are predictable. Here are the four you will encounter most often and what they point to.
| Problem | Cause | Fix |
|---|---|---|
| Flicker at low dim levels | Phase-cut mismatch between the dimmer and driver, or a circuit load near the dimmer's minimum threshold. | Try a trailing-edge dimmer. If the load is borderline low, a resistive dummy load raises the effective load without adding light output. |
| Buzz from the fitting or transformer | Driver resonance caused by the leading-edge's abrupt turn-on spike. | Switch to a trailing-edge dimmer. If buzz persists, the driver may not be rated for phase-cut dimming — check the datasheet. |
| Dropout at the bottom of the range | The driver's minimum dim threshold is lower than what the dimmer can cleanly deliver. | Check the dimmer's stated minimum dim level. A product listing 15% as its floor is fundamentally different from one listing 1% — this matters most in dining rooms and bedrooms. |
| Ghost glow when switched off | TRIAC dimmers allow small leakage current through the circuit even in the off state — some drivers respond by staying faintly lit. | Switch to a trailing-edge dimmer. For existing TRIAC installations, look for a "ghost eliminator" or bypass capacitor accessory from your dimmer manufacturer. |
Dimmer Compatibility with Dulora LED Globes and Drivers
Dulora’s dimmable GU10 range and dimmable filament globe range are verified compatible with trailing-edge and universal dimmers across the standard 240V residential and commercial spectrum. The GU10 and MR16 range carries a 40,000-hour lifespan and a three-year warranty. The 240V decorative filament range runs 25,000 hours at three years warranty. CRI 90+ across both; CRI 97+ on the ST64, G95, and G125 filament forms, where colour accuracy is non-negotiable.
For commercial and multi-zone applications, Dulora dimmers cover trailing-edge/PWM, 1-10V, and smart dimming options. The full product range is compatible with DALI, CBUS, and Diginet architectural control systems. For a deeper walkthrough of DALI commissioning, 1-10V wiring, and low-voltage driver selection, the 12V and 24V LED buyer’s guide covers the protocol-level detail.
As with any LED dimming chain, testing the specific dimmer-driver-globe combination in situ before committing to a full installation is the professional standard. An hour on-site before the order goes in saves considerably more than that in callbacks.
For commercial fit-outs, hotel refurbishments, or any project requiring DALI or architectural dimming system compatibility, contact us for specification support.
Frequently Asked Questions
Do I need a special dimmer switch for LED lights?
Yes. LED loads require a dimmer rated specifically for LED drivers, not incandescent or general resistive loads. Standard TRIAC dimmers can cause flicker, audible buzz, or premature LED driver failure when used with LED globes.
Always check the dimmer’s datasheet for its supported LED load range and confirm compatibility with your specific LED driver before installation.
What is the difference between leading-edge and trailing-edge dimmers?
Leading-edge (TRIAC) dimmers chop the front of the AC waveform and have a more abrupt switching characteristic, which can cause compatibility issues with LED drivers.
Trailing-edge dimmers cut the rear of the waveform, producing a smoother turn-on that is better suited to the capacitive input stage of most modern LED drivers. For new LED installations, trailing-edge dimmers are the recommended standard.
How does two-way dimmer switch wiring work?
A two-way dimming system uses one active dimmer module and one compatible slave or remote plate. The dimmer module performs all phase-cut control, while the slave plate sends control signals back to the dimmer via a low-voltage two-wire communication link between backboxes.
You cannot install two active dimmers on the same circuit. The slave plate must be a manufacturer-specified device designed to work with the same dimmer system.
Can I have a dimmer switch and a light switch on the same circuit?
A standard mechanical light switch in series with a dimmer module is not a supported configuration for most LED dimming systems.
The correct approach is to use a manufacturer-approved slave plate at the secondary location. These plates typically provide full on/off control and scene recall without introducing compatibility issues in the dimming circuit.
Can I install a dimmer switch without a neutral wire?
Some two-wire dimmers operate without a neutral by drawing a small parasitic current through the load. While this can work with certain LED drivers, performance is often less stable than neutral-connected installations.
Where a neutral conductor is available, it should always be used. If not, confirm that both the dimmer and LED driver are explicitly rated for two-wire LED operation.
How do I calculate the correct load for a dimmer switch?
Add up the total wattage of all LED fittings on the circuit. The final load should sit within the dimmer’s rated LED range, with sufficient margin for stable operation.
As a practical guideline, keep total load below 80% of the maximum rating and ensure it is at least 20–30% above the minimum load requirement.
Why are my LED lights flickering on a dimmer?
Flickering is usually caused by incompatibility between the dimmer and LED driver, a load below the dimmer’s minimum threshold, or a non-dimmable LED driver.
Start by confirming the driver is rated as dimmable. If the issue persists, check the dimmer’s LED load range or switch to a trailing-edge compatible unit.
Can I install a dimmer switch myself in Australia?
No. Under AS/NZS 3000 (Australian Wiring Rules), all fixed wiring work, including dimmer installation, must be completed by a licensed electrician.
A Certificate of Compliance must be issued upon completion. Unlicensed electrical work is illegal and may void insurance coverage in the event of an incident.