LED Strip Dimming: Which Protocol, and Which Driver

Why the driver decides everything

Constant-voltage LED strip is a passive load. It takes DC at a nominal voltage and produces light in proportion to what it is given. It has no intelligence, no protocol, and no opinion about dimming.

Everything that determines dimming quality happens upstream, in the driver. How deep it will dim, whether it flickers, whether it steps or glides, whether it turns fully off, whether it holds colour at the bottom of the range — all of that is a driver decision, made before anybody specifies a metre of strip.

This is worth stating plainly because it is the most common misunderstanding we encounter. Nobody has ever solved a flickering cove by changing the tape.

Mains dimming: leading edge and trailing edge

Both work by chopping the mains waveform. The dimmer sits in the mains circuit and removes part of each half-cycle; less waveform means less power. No separate control cable is needed, which is the whole appeal.

Leading edge, also called forward phase or TRIAC, cuts the beginning of each half-cycle. It was designed for incandescent lamps and inductive transformers, and it dates from a world where the load was a resistive filament that did not care how ugly the waveform was.

Two consequences follow. Leading edge dimmers usually have a minimum load — below it, the dimmer misfires and the light flickers or refuses to strike. A short strip run can easily fall below that threshold. And because the switching edge is abrupt, leading edge tends to be the noisier option: audible buzz from the driver or the dimmer itself is a common complaint.

Trailing edge, or reverse phase, cuts the end of each half-cycle instead. The switch-off is gentler, which suits the capacitive electronic loads that LED drivers actually present. It is generally quieter, generally smoother at the low end, and generally the better of the two for LED.

For both, one rule matters more than any other: the driver must be explicitly declared dimmable, and declared compatible with that dimming type. Mains dimming is a compatibility question, not a specification question. Reputable driver manufacturers publish tested dimmer compatibility lists. If the combination you are proposing is not on a list, you are testing it on site, at your own risk, in front of the client.

Mains dimming is fine for a small residential job. It is the wrong starting point for anything with zones, scenes, or a commissioning stage.

Analogue control: 1-10V and 0-10V

Both add a separate low-voltage control pair alongside the mains. The dimmer varies a DC voltage on that pair, and the driver reads it as a level. The mains supply stays clean and untouched, which is why analogue dimming is smoother than phase control almost across the board.

The difference between the two is which end drives the signal.

1-10V is the older standard. The driver supplies the voltage, and the control device acts as a variable resistor pulling it down. It dims to a minimum level — typically the "1" in the name — but it does not switch the light off. Turning off requires a separate relay or switch in the mains circuit.

0-10V is the current standard. The control device sinks current, and zero volts is a valid instruction. Whether zero volts means "minimum output" or "off" depends on the driver, and is often configurable. Do not assume.

Practical cautions for both. The control pair is polarity sensitive and getting it backwards is a classic site error. Voltage drop on long control runs will skew the dim level at the far end of a large installation. And a single control pair is a single zone — every driver on that pair does the same thing at the same time. Zoning means running more pairs.

DALI and DALI-2

DALI is a digital protocol. Instead of a voltage that means a level, the driver receives addressed digital messages on a two-wire bus. The bus is polarity-free, which removes the most common analogue wiring error, and it carries data in both directions.

That bidirectionality is the real difference. A DALI driver can be interrogated — it reports its status, and it will tell a maintenance system that a fitting has failed rather than waiting for somebody to notice. On a large site that is worth more than the dimming quality.

Each DALI line addresses up to 64 devices individually, with groups and scenes on top. Individual addressing means a single cove can be split into zones after the cable is installed, by commissioning rather than by rewiring. On a project where the lighting design is still moving during fit-out — which is every project — that flexibility is the reason DALI wins.

DALI-2 is the tightened version. The original standard covered control gear and left control devices loosely defined, which is how "DALI compatible" products ended up not always working together. DALI-2 extends certification to control devices and application controllers, and products are tested and registered rather than self-declared. It also formalises device types: DT6 for standard dimming, DT8 for colour control including tunable white.

If a project has any ambition — scenes, daylight linking, tunable white, integration with BMS — specify DALI-2 and specify certified product. The premium over generic gear is trivial next to the cost of a commissioning engineer diagnosing a bus that half works.

What separates a good driver from a cheap one

Protocol tells you how the driver is told what to do. It says nothing about how well it does it. Four things actually differ.

Minimum dim level. Cheap drivers stop somewhere in the low single-digit percentages and then drop out. Premium drivers keep going. As a reference point, eLDoLED's LINEARdrive constant-voltage range — the Dutch manufacturer now part of Acuity Brands, and the usual benchmark in this category — dims to 0.1%, with DALI-2 models configurable down to 0.02%. That is the difference between a cove that fades to nothing and a cove that snaps off at what the client will call "still quite bright".

Flicker. Most drivers dim by pulse width modulation: switching the output on and off faster than the eye can follow, and varying the ratio. If the switching frequency is low, the eye may not see it but a camera will, as banding across the shot. On any project with a hospitality or retail photographer in its future, this is not a technicality. Good drivers run PWM well above the range where this shows, and manufacturers who take it seriously state their flicker performance against the published standards rather than staying silent.

Dimming curve. Human brightness perception is roughly logarithmic, so a driver that reduces power linearly appears to do almost nothing across the top half of the dial and then plunge. Serious drivers offer selectable curves — eLDoLED's, for instance, default to logarithmic with linear and square available — so the dial behaves the way the person holding it expects.

Behaviour at the bottom. Reducing current alone shifts the colour of a white LED slightly as it dims. Pure PWM holds colour but becomes harder to keep flicker-free at very low duty cycles. The better drivers use a hybrid of both — eLDoLED market theirs as HydraDrive — precisely because neither method alone is good all the way to zero. If a specification is silent about how the driver behaves in the bottom 5%, assume it is not good there.

Traps specific to strip

One driver is one dimming zone. A continuous run fed by a single driver dims as a single object. If the design calls for the far end of a cove to behave differently, that requires a separate driver or a multi-channel driver, and it requires the cabling to have been planned for it. This is a first-fix decision, not a commissioning one.

Voltage drop is not a dimming problem. A long run that is dimmer at the far end is a power distribution problem. Dimming it will not help, and feeding the run from both ends usually will. See our guide on 24V and 12V for run lengths and feed planning.

Dimming does not hide a colour mismatch. Two reels from different production batches will differ, and dimming them together does not average that out — at low levels it often becomes more obvious, not less. See our guide on colour consistency.

Check the driver's minimum load against the shortest run, not the longest. The 12 metre run will be fine. The 1.5 metre return will be the one that flickers.

What to put on the drawing

Naming the protocol is not a specification. At minimum, state:

• Protocol, and for DALI whether DALI-2 certification is required
• Required minimum dim level, as a number
• Whether zero means off or minimum
• Flicker performance requirement where cameras or task areas are involved
• Number of channels and how zones map to them
• For mains dimming: the specific dimmer model, verified against the driver manufacturer's compatibility list

Every one of those is free to write at design stage and expensive to discover at handover.

What we supply

We supply LED strip: Bare LED Strip, COB LED Strip and Neon Flex 1010, cut to your specified length, at published per-metre rates with no minimum order.

We do not supply drivers, dimmers or controllers, and we have no commercial relationship with anyone who does. Most contractors and M&E consultants already have a preferred brand and dimming protocol, and that decision belongs with the electrical design — which is exactly why we are comfortable writing this page without recommending a product.