How to Dim a Dimmable LED Driver: A Specifier's Checklist (Flos Projects Included)

I've handled lighting orders and specifications for a design-driven firm for six years. I'm the person who buys and tests high-end fixtures before they go into a project—and also the person who documents our mistakes so the next project doesn't repeat them. Eleven significant mistakes, roughly $17,000 in wasted budget, and a lot of patient phone calls later, I maintain our team's checklist.

If you're asking how to dim a dimmable LED driver, the honest answer is: you don't dim the driver itself. You pair the driver with compatible control gear. This article is the checklist I wish someone had given me before that first expensive specification.

The mistake that started this

In September 2022, we specified 18 dimmable LED pendants for a restaurant renovation. The driver datasheet said “trailing edge.” The electrician installed leading-edge TRIAC dimmers because that's what they always used for LEDs. At full brightness, everything looked perfect. Below 40%, the fixtures buzzed and flickered. Two drivers wouldn't restart after being dimmed down.

The fixtures were not defective. The controls were not compatible. Replacing the dimmers cost about $2,400 plus a rushed weekend and a one-week delay. That's when I started writing down every assumption I'd previously made about dimmable lighting.

Step 1: Confirm the driver is actually dimmable

Not every LED driver is dimmable. Fixed-output drivers are common, and they are not defective if they were specified that way. The problem starts when a dimmer is installed on one that can't accept chopped waveforms. The result is usually flicker and, in some cases, an early failure.

Read the driver or fixture spec line by line. If the word “dimmable” and the dimming method aren't there, assume it isn't dimmable. If the fixture is a classic model that has been reissued—say, a Taccia lamp Flos from a few years ago—confirm the current data sheet, because source types and driver specifications change. I don't have hard data on how often this causes field callbacks, but anecdotally, a lot of them start with “I thought it was dimmable.”

Step 2: Identify the dimming protocol

“Dimmable LED driver” is only half a sentence. The full sentence should say what control protocol the driver expects:

• Leading-edge phase-cut (TRIAC) is common with older residential dimmers.
• Trailing-edge phase-cut (ELV) tends to be smoother for many LED drivers.
• 0–10V uses separate control wires for analog dimming.
• DALI is addressable digital control, common in commercial projects.
• DMX or wireless protocols like Casambi are used when you need scene control or integration.

For a wall-box dimmer, a phase-cut driver is usually the right answer. For a building management system, 0–10V or DALI is probably what you want. The driver data sheet will tell you. If it only says “dimmable” without a method, don't guess. Ask before you buy.

Here's where product differences matter. The portable Flos IC Lights S1 version I last specified doesn't need an external wall dimmer at all—its dimming is built into the fixture's touch control. So the phrase “Flos IC Lights S1” on a project does not mean the same thing as “Flos product with a dimmable LED driver to integrate.” The correct answer depends on the specific product page and data sheet in front of you.

Step 3: Match leading-edge and trailing-edge to the dimmer

People assume a phase-cut dimmable driver works with any phase-cut dimmer. Actually, drivers are usually designed for one edge, not both, unless the spec says otherwise. Trailing-edge drivers paired with leading-edge TRIAC dimmers are the classic mismatch: buzzing, poor low-end control, and occasionally no restart after turn-off.

The fix is boring and effective: check the spec for “leading edge” or “trailing edge,” then write the dimmer model number into the electrical schedule. If the project needs to be changed later, revisit compatibility before installation, not after.

Step 4: Use the manufacturer's compatibility list

Most reputable manufacturers publish tested dimmer lists. Flos and driver suppliers provide these in spec sheets, or their representatives can email them. Do not rely on a generic “this dimmer works with LEDs” from the hardware store shelf.

Here's something vendors don't always say: a compatibility list is a list of what was tested, not an exhaustive guarantee. If the dimmer you want isn't listed, ask in writing. If the vendor confirms, keep the email. If they won't confirm, buy one sample and test it before you order the rest.

Step 5: Check minimum load, maximum load, and neutral wire

Dimmers have load limits, including minimums. A single tiny LED table lamp on a 600W dimmer can behave poorly—some stay lit when off, some blink, some don't reach low dimming. Many modern LED dimmers also require a neutral in the wall box.

The low-end trim is the step most people ignore. If fixtures cut out at 20% but the design calls for 5%, check whether the dimmer has an adjustable low-end trim. In my first year, we sent a crew on an $890 call-out because no one had set the trim on four dimmers. Not a product failure. A settings failure.

Step 6: Build a mock-up and test the actual combination

A paper compatibility list is helpful, but a one-fixture test is better. Use the actual driver, the actual dimmer, the actual LED module, and the actual wiring setup. Test at full brightness, 50%, 10%, and minimum. Then switch off and on at low settings. Watch for visible flicker, and take a slow-motion phone video if you can—cameras often pick up strobing that the eye misses.

This step feels excessive when the project timeline is tight. But an hour of mock-up testing is cheaper than replacing 18 fixtures on site. Since I created a pre-order test list in Q1 2024, our team has caught 47 potential errors in the last 18 months. That list started after my third rejection in one quarter, and it's paid for itself many times over.

Step 7: Record what was installed for the people who come after you

After installation, write down not just fixture names but dimmer models and driver settings. Put them in the operation and maintenance manual. Facility teams shouldn't have to guess when they replace a dimmer five years later. I've seen that guessing game turn into a whole new compatibility investigation, and it always costs more than the half hour of documentation would have cost.

The 30-second version

1. Confirm the driver is marked dimmable and state the protocol.
2. Match leading-edge or trailing-edge to the actual dimmer.
3. Check the manufacturer's compatibility list.
4. Verify minimum load, maximum load, and neutral availability.
5. Set the low-end trim.
6. Test the actual fixture, dimmer, and driver combo before a large order.
7. Document installed models and settings.

Spotlight synonyms: useful in writing, dangerous in specs

Since I keep a team checklist and write our newsletter, I once wrote a volunteer spotlight about a colleague who spent a weekend helping with a community lighting project. In writing, synonyms like highlight, feature, honor, or shine a light on are useful. In a lighting schedule, they aren't interchangeable. A “spotlight” in this industry is an actual fixture with beam angle, field angle, mounting, and dimming requirements. If the drawing says “spotlight the wall,” that's a conversation, not a specification. Use the exact product reference and the photometric data. Then apply this checklist to its driver.

If you came here looking for volunteer spotlight language, the thesaurus approach works for people, not for photometrics. If you came here to make dimmable fixtures behave, the checklist above works.

Verify before you buy

This checklist worked for our projects, but our situation is commercial and hospitality work. If you're specifying for a home or working on an international project, local electrical codes and available controls are different. Always verify current product specifications at flos.com; for example, the current Taccia lamp Flos page and the Flos IC Lights S1 page will tell you what driver and dimming options are actually available today. I can only speak to my context and my mistakes—but those mistakes were expensive enough to make me read data sheets.