Why Do LED Spots Flicker When Dimming? – The Most Common Causes and Solutions

Picture this: you flip the switch, the LED spots come on, everything looks great. Then you touch the dimmer — and the flickering starts. Sometimes it's subtle, something you almost convince yourself you're imagining. Other times it's blatant, making the room feel less like a smart home and more like a haunted one.

So what's actually going on?

Here's the thing: the LED fixture itself is almost never the culprit. Flickering during dimming almost always comes down to an interaction between your dimmer, the LED driver, and how the circuit is wired. In most cases, once you know where to look, the fix is straightforward. This article runs through six of the most common causes and what to do about each one.

Cause 1 – Your Dimmer Wasn't Made for LEDs

This is the number one reason I see in the field. The dimmer on your wall was probably designed for incandescent or halogen bulbs — even if it looks modern. Most leading-edge and trailing-edge TRIAC dimmers work by chopping sections off the mains voltage sine wave to reduce power. That approach works fine for a 60 W halogen bulb, which behaves like a straightforward resistive load. An LED driver doesn't behave the same way at all.

The telltale sign: your spots flicker or strobe at mid-to-low brightness levels, but stay steady at full brightness. You might also notice that swapping in a different brand of LED spot changes the behavior — which is a dead giveaway that the dimmer is the common denominator.

Here's the uncomfortable truth about this one: matching a 230 V TRIAC dimmer to LED spots is one of the most notoriously difficult compatibility problems in the lighting industry. No matter how reputable the dimmer brand, you will hit edge cases where things don't work cleanly together. The fundamental issue is that TRIAC dimmers were never designed for the highly non-linear, capacitive load that an LED driver presents — and every manufacturer's driver circuit reacts slightly differently. In practice, what this means is that even the best dimmer manufacturers can't guarantee 100% compatibility across all LED products. They handle it by publishing a tested compatibility list: specific dimmer models paired with specific LED lamp references that they have verified in their labs. So if you are buying a TRIAC dimmer — or LED spots that are designed to work with TRIAC dimmers — always check the manufacturer's compatibility list before committing. If your LED spot isn't on it, the odds of a clean dimming experience go down considerably.

Cause 2 – The Dimmer's Minimum Load Isn't Met

Every trailing-edge dimmer specifies a minimum load. On older dimmers designed for halogen, that minimum might be 20–40 W. An LED spot draws 3–12 W. Sounds like you'd need a lot of them to hit that threshold — and technically, you might. But here's the catch: the LED driver's actual load behavior doesn't look like a resistor to the dimmer. So even when the wattage math technically checks out, the dimmer can still misbehave.

Watch for this: flickering that only shows up when you dim down below about 30–40 %. Above that, things are usually fine. The spots work perfectly well when the dimmer is cranked up.

Cause 3 – The PWM Frequency Is Too Low

Here's one that catches people out even after they've sorted the dimmer. Many LED controllers dim by switching the LED current on and off very rapidly using Pulse Width Modulation (PWM). The duty cycle — how long the pulse is on versus off — determines the brightness. The frequency of those pulses is what matters here.

If the PWM frequency is below roughly 100–200 Hz, your eye picks it up, especially in peripheral vision or when you move your head quickly. You might not consciously "see" the flicker, but it can contribute to eye fatigue and that vague uncomfortable feeling you get in some dimly lit rooms. In lighting engineering circles, this is called Visible Flicker.

Quick test: point your phone camera at the spot through the viewfinder (not the screen preview) and look for strobing on the image. If it's there on camera but not visible to the naked eye, you've found your culprit.

Cause 4 – The CC LED Driver Has a Ripple Problem

Constant current LED drivers are responsible for more flicker problems than most people realise — and the causes split into two distinct mechanisms, both easy to miss if you don't know where to look.

The first: current ripple and load-step response speed. On paper, a constant current driver rated at 350 mA delivers 350 mA — steady and clean. In reality, the output isn't a flat line. Hook up an oscilloscope and you'll see a sawtooth waveform: the driver monitors current, corrects it, over-corrects slightly, corrects again, and repeats. That repeating error — engineers call it Ripple Current — is normal even in quality drivers. The amplitude depends on the size of the output filter capacitor. A well-designed driver keeps the ripple small; a cheaper one lets it swing wider. Either way, the current isn't perfectly flat, and at low dimming levels, your eye is less forgiving.

The second: LED forward voltage threshold. Here's the nuance that often gets left out of driver discussions: in a constant current driver, current is held constant, but voltage is not. A 350 mA driver might present a voltage window of 36 V to 58 V to the LED depending on dimming level and load. As you dim lower, current stays at 350 mA but the voltage headroom shrinks. If the ripple trough ever dips below the LED's forward voltage threshold during the sawtooth cycle, the LED temporarily drops out — going dark for a fraction of each cycle. That's when you get visible flicker or dropout at low dimming levels, independent of the dimmer.

Constant voltage drivers have a parallel problem: dynamic response speed. A CV driver maintains a fixed output voltage — 24 V, say — but what happens when the load changes? As dimming or other loads on the same circuit cause the current draw to fluctuate, the driver's voltage briefly dips before recovering. The spec that governs this behaviour is called dynamic response (sometimes listed as load transient response or voltage recovery time). A fast dynamic response means the driver snaps back to 24 V almost instantly. A slow one means the voltage sags for a measurable moment, the LED dims or flickers in sympathy, and you see it. Cheap CV drivers routinely spec poorly here, and it shows under real-world dimming conditions.

Rule it in or out: if your spots flicker even when the dimmer isn't being touched — same flicker level at 80 % as at 30 % — and swapping the dimmer makes no difference, the driver is almost certainly the problem.

Cause 5 – Voltage Drop on Long Cable Runs

This one shows up in installations where the power supply is a long way from the spots. Run 24 V LED cable over too great a distance without accounting for conductor size, and the voltage at the far end of the run drops below what the driver expects. Instead of 24 V, your furthest spots might be seeing 21 V or less.

Low voltage makes the LEDs dimmer than intended. More problematically, the driver electronics operate outside their intended working range. The result: instability, erratic behavior, and flickering that gets worse the more spots are turned on simultaneously.

This is exactly the problem the TILLUME 24 V LED 2850 K Spot Dimming series was designed to address. Rather than relying on the driver alone to maintain regulation at the low end of the voltage window, TILLUME built a dedicated wide-input regulation circuit directly into the spot module itself. The result is that the module continues to deliver its rated current — and therefore its rated brightness — even when the voltage at the module drops to 21.5 V. In practice, this gives installers substantially more headroom when routing cable over long distances, without sacrificing light quality at the far end of the run.

Watch for this: the spots furthest from the power supply flicker worst. When you turn off some of the nearer spots (reducing total load), the far ones might stabilise — because there's less current flowing and less voltage drop.

Cause 6 – Electromagnetic Interference on the Circuit

Sometimes the problem isn't inside the LED circuit at all — it's bleeding in from elsewhere. Motors, switched-mode power supplies, and other equipment on the same electrical circuit can inject high-frequency noise into the LED driver, causing the driver output to fluctuate. Even the dimmer itself can be the source, reflecting switching transients back into the mains.

The clue: flickering that comes and goes depending on what else is running. Turn on the kitchen extractor fan, and the dining room spots start flickering — even though they're supposedly at a constant dimming level.

LED Afterglow – When the Light Doesn't Turn Off Properly

Afterglow — sometimes called Ghosting — isn't technically flickering, but it gets confused with it all the time. After you turn the switch off, the LEDs keep glowing faintly for anywhere from a few seconds to several minutes. It's unsettling, and it makes people think their dimmer or driver is broken.

The mechanism is different from flickering. Residual voltage is getting to the LED driver through parasitic capacitance in the wiring or through the neutral conductor. A tiny current — way too small to register under normal conditions — is enough to weakly excite the LED into emitting a faint glow. Electronic dimmers combined with LED drivers that lack proper discharge circuitry are the most common culprit.

Choosing a Dimming System That Won't Give You Headaches

Worth stepping back and looking at the options. Here's how the main dimming approaches compare:

Conclusion – Flickering Is Fixable

If your LED spots flicker when you dim them, don't accept it as normal. It's not a quirk of LED technology — it's a solvable problem, and usually a straightforward one.

The most common culprits are dimmer incompatibility, undersized minimum load, and low PWM frequency. All three are fixable with the right components. For new projects, the real move is to design the system properly from the start: pick a dimming protocol (DALI is my strong recommendation), match it to properly specified components, and pay attention to cable sizing and circuit layout.

A 24 V constant voltage architecture has real advantages here. The lower voltage means voltage drop is less of an issue over longer runs. The separate control electronics let you run high-frequency PWM without compromise. And parallel wiring — standard on constant voltage systems — is more forgiving of installation mistakes than series wiring. That's exactly why TILLUME builds on constant voltage: it eliminates several of the root causes of flickering from the design stage.

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