Dimmable LED Power Supply: 0-10V vs PWM vs DALI vs TRIAC

Dimming to 50% does not cut your power bill by 50%. LED efficacy rises as drive current falls, so halving the light typically leaves you at roughly 60% of input power — and then the driver’s own efficiency drops 3–5 points at light load, landing you near 63–65%. Anyone budgeting energy savings from a dimming retrofit is overstating the return by about a third. The real reasons to dim are glare control, scene setting and lamp life — not the electricity.

Which dimming method you specify decides what cable you pull, what controller you buy, and whether the installation flickers. Here is what each one actually does on site.

The Four Methods, Side by Side

0-10V: The Workhorse, With a Catch

The controller sinks current from the driver’s 0-10 V pair. 10 V = 100% output, 1 V = 10%, and the driver’s internal pull-up sits around 10 V with a 0.5–2 mA source.

Two things go wrong on site.

First: 0 V does not mean off. Almost every 0-10 V driver shuts down at the bottom of its range — usually 10% output at 1 V — and continues drawing standby power. If your spec says “lights off at scene 4,” you need a mains contactor or a relay in the driver. Leaving a driver sitting at its 10% floor for 12 hours a night still consumes power and still ages the output capacitors.

Second: the two wires are polarity-sensitive and they are easy to swap. Reversed 0-10 V wiring usually presents as “dimming works backwards” or “no dimming at all.” Check before you blame the controller.

0-10 V also degrades over distance. At 30 m on 0.75 mm² control cable the signal loses enough to shift the dim floor by several percent. Keep control runs under 25 m or use a signal repeater.

Our 100 W, 150 W and 200 W dimmable units accept TRIAC and 0-10 V on the same chassis, which covers the two most common retrofit cases without stocking two SKUs.

PWM: Cheap, and Where the Flicker Comes From

PWM switches the output on and off faster than the eye resolves. 200 Hz to 1 kHz is typical; duty cycle sets perceived brightness.

The problem is that “faster than the eye resolves” is not the same as “safe.” IEEE 1789 sets flicker risk thresholds, and the practical guidance is that below about 1,250 Hz you should keep modulation depth under roughly 10% to stay in the no-risk band. Cheap PWM drivers running 200 Hz at 100% depth are the source of most “the lights give me a headache” complaints — and of the strobing you see when someone films the installation on a phone.

PWM is a good choice for battery-powered and low-voltage DC installations where wiring distance is short. For commercial interiors with cameras present, specify ≥1 kHz or use DALI.

DALI: The Only One That Is Actually a System

IEC 62386 gives you 64 addresses, 16 groups, 16 scenes and two-way communication — the driver reports status and lamp failure back to the controller. Bus speed is 1,200 baud over 2 wires, maximum bus length 300 m, and the bus is polarity-free, which removes the single most common wiring error in 0-10 V installs.

DALI costs more per driver and requires commissioning. It earns that back on anything above roughly 30 fixtures, or anywhere you need per-fixture addressing, emergency test reporting, or reconfiguration without rewiring.

DALI-2 adds standardised control-device profiles, which is what you want if you are mixing drivers and sensors from different vendors.

TRIAC: Retrofit King, Compatibility Minefield

TRIAC dimmers cut the mains waveform on the input side — leading edge (forward phase) or trailing edge (reverse phase). No new cable, which is why it dominates retrofit.

The failure mode is predictable and almost always diagnosed wrong. A TRIAC dimmer rated 600 W was specified for an incandescent load. Your LED load is 60 W. The dimmer needs 10–20% of its rating as a minimum load to hold its timing circuit stable, and 60 W on a 600 W dimmer is 10% — right at the edge. Result: flicker at low end, drop-out, or audible buzzing.

The instinct is to fit a bigger dimmer. That is backwards — a bigger rating raises the minimum load requirement and makes it worse. The correct fixes, in order:

1. Use a driver with an active bleeder / dummy load circuit (most modern LED drivers have one)
2. Fit a dimmer explicitly rated for LED loads, typically 10–150 W
3. Use trailing-edge dimming, which behaves better with capacitive driver inputs

Check the driver’s datasheet for a statement like “compatible with leading and trailing edge dimmers” plus a minimum load figure. If no minimum-load number is published, ask for it.

Four Wiring Traps

1. Running dimming pairs in the same conduit as mains. 0-10 V and DALI are low-voltage signal circuits; parallel runs with 230 V mains induce enough noise to cause random dimming. Keep ≥50 mm separation or use a separate conduit.
2. Daisy-chaining more drivers than the control source can sink. A 0-10 V controller sinking from 20 drivers exceeds its current rating and the dim floor rises. Most controllers drive 20–50 drivers; check and split into zones.
3. Mixing dimming types on one driver. Obvious in theory, common on site when a replacement unit arrives with a different control input.
4. Forgetting that dimming changes the load calculation. A dimmed system rarely draws full power, but you still size the driver for the undimmed load — at 100% scene, all zones are at full output. See Signage Power Supply Load Calculator: Sizing Worksheet and the 24V vs 12V voltage drop math if you are running long feeds.

How to Choose

What to Put in the RFQ

Seven fields, and the last three are the ones usually missing:

1. Dimming method (0-10 V / PWM / DALI / TRIAC / none)
2. Dim range floor — 10% or 1%?
3. Flicker performance at the floor (ask for a percentage, not “flicker free”)
4. Minimum load for TRIAC
5. Does 0 V actually switch off, or does it need a relay?
6. Number of drivers per control circuit
7. Dimming curve — linear or logarithmic (log matches human perception; linear looks wrong at the low end)

Send us your dimming method, fixture count and run lengths — we will confirm which of the 100 W / 150 W / 200 W dimmable units fits and whether you need a relay for true off. → Request a quote · See the 150 W dimmable unit