Before choosing a dimmer there is one thing to accept that surprises a lot of people: you do not choose the technology; the light fitting imposes it. If the driver speaks 0-10 V, no amount of preference will let you dim it with a phase-cut dimmer.
There are four ways to dim a light, and each manipulates something different.
| What it manipulates | Control wiring | Where it is used | |
|---|---|---|---|
| Phase cut | The 230 V waveform | No | Dimmable bulbs at home |
| 0-10 V | A control voltage | Yes, two wires | Commercial and technical lighting |
| DALI | Digital messages | Yes, a bus | Large installations |
| PWM | Time spent on | Separate controller | 12 and 24 V LED strips |
Phase cut: the domestic one
The one we have always had. The dimmer cuts away part of each half-cycle of the mains waveform: the more it cuts, the less energy arrives and the dimmer the light. Its great advantage is that it needs no extra wiring: it goes where the switch was and drives the bulb directly.
Leading or trailing edge
Leading-edge cutting removes the start of the half-cycle. It was designed for incandescent bulbs and magnetic transformers, and with LEDs it tends to buzz and flicker.
Trailing-edge cutting removes the end: the waveform starts from zero and rises progressively, with far less buzzing and flicker on LEDs. It is what the Shelly Dimmer Gen3 uses.
The bulb has to be dimmable. No dimmer makes a non-dimmable LED dimmable.
0-10 V: the analogue one
Here power and control take separate paths. The fitting gets its normal 230 V, and a separate pair of wires carries a 0 to 10 V DC signal that the driver reads as a brightness level. It is the norm in warehouses, offices and high-power floodlights, and it needs a driver with a control input: it is no use for an ordinary bulb.
DALI: the digital one
Instead of a voltage, a digital bus carries messages with specific commands. It is a standard — IEC 62386 — designed for large installations, and its appeal is individual addressing: every fitting has its own address and can be dimmed separately.
Careful: not everything that speaks DALI makes use of that. The Shelly DALI Dimmer Gen3, for one, drives the whole bus as a single group. Check before you buy.
PWM: the LED-strip one
Pulse-width modulation switches the load on and off hundreds of times a second. The eye does not see the flicker, only the average: the longer it stays on in each cycle, the brighter. It is how 12 and 24 V DC LED strips are dimmed; it does not work for 230 V bulbs, and it needs a controller between the power supply and the strip.
Which one is yours
Look at the fitting and answer one question: what does it accept as input?
- A dimmable 230 V bulb → phase cut.
- A driver with Dim+ and Dim− terminals → 0-10 V.
- A driver with DA terminals or marked DALI → DALI.
- A 12 or 24 V LED strip → PWM.
Frequently asked questions
Can I use a phase dimmer on a 0-10 V driver?
No. Chopping the supply of a driver that expects a steady voltage can cause flicker, erratic behaviour, or damage.
Why does my dimmable LED flicker at the low end?
It is usually the combination of cutting method and the bulb’s electronics. Raising the minimum brightness in the dimmer’s settings fixes a good share of cases.
Does phase cutting save energy?
Yes, though not in proportion to the brightness you perceive: the eye responds logarithmically, so at 50 % power the light looks a good deal brighter than half.
What if I have no neutral?
Only phase cutting has options. The Shelly Dimmer Gen3 works without neutral; under 20 W it will need a bypass.
Which dims best at low levels?
DALI and 0-10 V, because the command travels separately from the power. It is one of the reasons they dominate professional lighting.