Dimmable LEDs and dimmers: phase cut, 1–10 V and DALI explained

Written by Engin Demirel · Electrical technician, master instructor · 12 years of experience

Short answer: To dim an LED, both the fixture's driver and the control (dimmer) must support the same dimming method. In homes the most common method is a phase-cut (triac) wall dimmer; projects use 1–10 V and digital DALI. Connecting a dimmer to an LED that is not marked "dimmable" causes flicker, buzzing and failures. When choosing a dimmer, check its LED rating and which dimmer type the driver has been tested with.

Why not every LED dims

With an incandescent bulb, the dimmer lowers the voltage, the filament runs cooler and the light drops. With an LED, the light is set by the driver in front of it. If the driver is not designed to read the chopped mains waveform and reduce the LED current accordingly, the light either does not dim at all or flickers erratically. So a "dimmable LED" really means "an LED with a dimmable driver".

Dimming methods

Phase cut (triac): The wall dimmer cuts part of each mains half-wave. There are two kinds: leading edge (RL) and trailing edge (RC). LED drivers usually run quieter and flicker-free on trailing edge. No extra wiring is needed; it fits the existing switch box.
1–10 V / 0–10 V: A separate two-core control line runs to the driver next to the power cable; the light level follows the voltage on that line. Simple, stable and common in offices and shops.
DALI (DALI-2): Digital, addressable communication. Up to 64 drivers are addressed on the same two-core line; every fixture can be dimmed individually, groups and scenes can be set and it talks to sensors and building automation. If the colour temperature should also change, a DALI DT8 driver is needed.
Push-dim (Touch DIM): A normal push button dims when held and switches on/off with a short press. Handy for small groups.
PWM: For LED strips, a controller between driver and strip dims by switching very fast; controlled by remote, wall unit or app.
Smart systems (Zigbee, Wi-Fi, Matter): Smart bulbs or smart dimmer modules dimmed from a phone or voice assistant.

Why LEDs flicker or buzz

Driver and dimmer are not compatible (the most common reason). Check the manufacturer's list of compatible dimmers.
The dimmer's minimum load is not reached: older dimmers are built for 40–60 W and more and behave erratically with two or three 7 W LEDs.
The dimmer's capacity is exceeded: LED drivers draw a high inrush current at switch-on. The "LED max." rating on the dimmer is far below its incandescent rating; size by that value.
Different brands and types of fixtures are mixed on one circuit.
A leading-edge (RL) dimmer is used with a driver that expects trailing edge.

Which one to choose

One room, existing switch: a trailing-edge LED dimmer plus fixtures marked "triac dimmable".
A few fixture groups in a new installation: push-dim or 1–10 V; if cables are being pulled anyway, lay the control line now.
Offices, hotels, shops, villas: DALI. The most flexible choice for scenes, sensors, daylight dimming and building automation.
Cove lighting, shelf and under-cabinet LED strips: a PWM controller or a dimmable constant-voltage driver.

Dimming magnetic track and Lamptime fixtures

Many Lamptime fixtures offer "DALI" as a control option on the product page; the default version has an on/off driver. In a magnetic track system, dimming is done by the driver that feeds the track. In our magnetic track planner you can tick the DALI option and the system is calculated accordingly. The DALI control (wall panel, sensor or smart home hub) is planned separately.

Installation tips

The dimmer, the driver and the control line should be chosen together in the same design. In new buildings, bringing a neutral to the switch boxes and leaving a separate control core for DALI or 1–10 V avoids chasing walls later. For villa, apartment and office projects in Bursa, Turkey, we plan lighting control together with the electrical installation.

Frequently asked questions

Can every LED bulb be dimmed?

No. Only LEDs marked "dimmable" on the pack or label, with a driver designed for dimming, can be dimmed. Others flicker or fail on a dimmer.

Why does my LED dimmer flicker?

The most common causes are an incompatible driver and dimmer, a load below the dimmer's minimum and exceeding the dimmer's LED rating. A trailing-edge LED dimmer and products on the manufacturer's compatibility list usually solve it.

What is the difference between DALI and 1–10 V?

1–10 V dims a whole group with an analogue signal. DALI is digital: every driver gets an address, fixtures can be dimmed individually, scenes and sensors can be added and the driver can report its status.

How many watts of LED can a dimmer handle?

Check the LED rating printed on the dimmer; it is much lower than the incandescent rating. The total LED load must be below this limit and above the dimmer's minimum load.

Can a smart bulb be used with a dimmer?

No. Smart bulbs dim internally and may fail if a dimmer is placed in front of them. Use a normal switch on that circuit and keep it powered.