Everything You Need to Know About Dimming
Dimming should be simple. You slide something up and down, the light politely follows, and everyone feels like they live in a tasteful restaurant.
But then you install “a dimmable bulb,” and suddenly you’ve got flicker, buzzing, lights that won’t turn on until 30%, or a dimmer that behaves like it’s negotiating for better wages.
The reason isn’t that dimming is broken. It’s that different light sources dim in completely different ways, and different dimmers “ask” for dimming differently. Incandescent dimming was the golden age because the technology was forgiving. Everything after that became a little more “systems-based.”
Here are all the facts about dimming we explain at the counter all the time…
Incandescent: the original dimming champion
Incandescent bulbs dim beautifully because they’re a resistive filament — a tiny wire designed to get hot enough to glow. When you reduce the electrical energy going into that filament, it gets less hot, so it glows less. Nothing clever. Nothing fragile. Just physics doing its thing.
They’re also incredibly smooth when dimmed because a filament has thermal inertia. It doesn’t instantly change temperature. Even if the electricity feeding it is a bit choppy, the filament sort of “averages it out” and stays steady. That’s one reason incandescent dimming looks so pleasant compared to a lot of modern dimming problems.
And then there’s the part everybody remembers: incandescents become warmer in colour as they dim. That cozy amber glow isn’t a special feature — it happens because the filament is literally cooler. As it cools, its spectrum shifts toward longer wavelengths (more amber/red), so the light looks warmer. In short: less power, cooler filament, warmer-looking light. It’s the most emotionally satisfying failure of energy efficiency ever invented.
The classic wall dimmer: the old wheel/knob everyone had
Most people grew up with that rotary knob dimmer — sometimes with a push-on/push-off function. That style became common because it was perfectly matched to incandescent loads. In a world of glowing filaments, a dimmer could be pretty crude and still feel buttery smooth.
The problem is: we kept installing the same idea of dimmer into a world where “a light bulb” became an electronic device. So the control method stayed, but the loads changed dramatically.
Which brings us to what a traditional dimmer is actually doing.
How most “traditional” dimmers actually dim (the waveform chop)
Power coming out of your wall is AC (alternating current), which means it isn’t a steady stream — it rises and falls in a smooth, repeating wave. In North America that happens 60 times per second, and because each cycle has a positive half and a negative half, the “action” resets 120 times per second. Incandescent dimming worked so well for so long because the control method and the light source were basically made for each other: the dimmer could hack up the wave, and the filament would still behave nicely.
A traditional wall dimmer doesn’t really “turn the voltage down” the way a faucet reduces water flow. Instead, it uses an electronic switch (often a TRIAC in older designs) to block power at the start of each half-wave, then let it through partway along. The dimmer decides how late in the wave it will “open the gate.” The later it opens, the less of that wave gets delivered, and the lower the average power reaching the lamp. Do that 120 times per second and you get a controllable reduction in light output — not by smoothing power down, but by chopping away slices of the waveform.
A good way to picture it is a conveyor belt delivering boxes of energy. The dimmer isn’t slowing the belt down. It’s simply shutting the belt off for a portion of every cycle, then turning it back on. At full brightness, the belt runs almost the whole time and the lamp gets almost all the boxes. At lower settings, the belt is “off” longer, so fewer boxes arrive each second. The lamp receives less total energy, so it produces less light.
Now here’s why incandescent bulbs were such easy customers: a filament is basically a tiny resistive heater with a lot of thermal inertia. Think of it like a cast iron pan on a stovetop. If you pulse the burner on and off rapidly, the pan doesn’t instantly cool down and heat up — it averages the heat over time. That’s exactly what an incandescent filament does. Even though the dimmer is feeding it chopped-up packets of power, the filament’s temperature changes slowly enough that it smooths out those pulses and produces steady-looking light.
There are also two common “styles” of phase chopping. Older dimmers are often leading-edge, meaning they cut off the front of each wave and then snap power on partway through. Newer electronic dimmers are often trailing-edge (sometimes marketed as ELV dimmers), which let the wave begin more naturally and then cut it off early. The practical point isn’t that one is always better — it’s that different loads and power supplies respond differently depending on how the waveform is being chopped. Incandescents don’t care much either way. Anything with electronics inside it might care a lot.
Fluorescent dimming: possible, but it was never “simple”
Fluorescent lighting doesn’t work by heating a filament. It creates a controlled electrical discharge (an arc) in a gas, producing UV light that hits phosphors to create visible light. So dimming fluorescent is less like “turning down a heater” and more like “asking an arc to behave politely at lower power.”
That’s why fluorescent dimming historically required the right ballast and the right control method. A standard fluorescent ballast isn’t automatically dimmable, and even dimming ballasts have limits on how low they can go while staying stable. This is also why fluorescent dimming often felt more “technical” than residential dimming — because it really is a coordinated system.
If you’ve ever seen fluorescents that flicker, drop out, or do weird stepping when dimmed, it’s usually the arc struggling to remain stable while the system tries to reduce output.
LED dimming: you’re not dimming a bulb, you’re dimming electronics
LEDs are neither a heated wire nor a gas discharge. They’re semiconductors that want controlled current. That’s why most LED lamps and fixtures contain a driver (built-in or external) that converts and regulates power.
So when you dim LEDs, one of two broad things is happening:
- You’re using a phase-cut dimmer (the wall dimmer is chopping the waveform), and the LED driver is trying to interpret it and respond nicely.
- Or you’re using a control method that speaks directly to the driver (like 0–10V), and the driver is doing the dimming internally.
LED dimming can be incredibly smooth, deep, and consistent — but only when the driver and control method are compatible. When they’re not, you get: flicker, buzz, dropout at low levels, popping on, uneven dimming, or a dim range that feels like “100%… 95%… 90%… 12%… off.”
This is also where the difference between “dimmable” and “dims well” matters. Some products will technically dim, but they won’t do it gracefully.
0–10V dimming: the commercial approach
0–10V dimming is common in commercial lighting because it separates the control from the power. The driver gets full power, and a low-voltage signal tells it what output level to run. This tends to produce predictable behavior in large installations because the driver is in charge of the dimming, not the wall dimmer trying to chop power and hoping the driver plays along.
It’s not that 0–10V is magically perfect — driver quality still matters — but it’s a more deliberate language between control and fixture, especially in bigger projects.
Step dimming, “high/low” switches, and why some fixtures won’t do it
A lot of people assume “high/low” is basically the same thing as dimming, but historically it was often a different trick. You see (or used to see) high/low switches in places like table lamps, older floor lamps, range hoods, bathroom fan/light combos, and some older utility fixtures. The goal wasn’t a smooth fade — it was simply “bright mode” and “calm mode,” usually with a little switch.
With incandescent and many halogen lamps, this was easy. Those light sources in both are resistive filaments: change how much power they get and they’ll happily land at a different brightness without complaining. That’s why incandescents are still the “safest bet” for a true high/low setup, and why halogens in range hoods have remained a common choice for so long — it behaves predictably, and it doesn’t require a power supply to interpret what you meant.
Modern LED bulbs are different because they usually contain electronics (a driver) that wants to operate in a specific, stable mode. A basic high/low switch doesn’t give the driver a clean “command” — it typically just changes the input conditions in a way the driver wasn’t designed to interpret. The result is why off-the-shelf LEDs often won’t behave properly in high/low fixtures: they may flicker, drop out, flash, stay stuck on one level, or simply not work.
If you want high/low behavior with LEDs, you generally need a product that’s explicitly designed for step dimming (sometimes called step-dim, multi-level, or selectable output). Those products have a driver that expects a two-level input or a defined control method. Without that, a high/low switch can’t magically force an LED driver into two stable brightness modes.
Dim-to-warm: how LED recreates the incandescent vibe on purpose
Incandescent gets warmer as it dims because the filament cools.
LED doesn’t do that naturally — so “dim-to-warm” LED products imitate the effect by mixing multiple LED channels (cool + warm) under driver control. As you dim, the driver turns on warmer LEDs. It’s basically engineered nostalgia, and when it’s done well it’s genuinely lovely.
Quality bulbs and good dimmers matter
If dimming feels unpredictable, it’s usually because the dimmer and the lamp/driver are each doing their own thing — and neither one is obligated to be polite about it.
Cheap bulbs (think “dollar-store energy efficiency”) often cut corners on driver design and component quality. Even if they say “dimmable,” they’re more likely to buzz, flicker, or have an ugly dim curve where everything happens in a tiny slice of the slider. Cheap dimmers can also struggle with low loads, poor waveform control, or noisy electronics.
If you want dimming to feel like the old incandescent days — smooth, quiet, and predictable — you generally need two things: a decent dimmer designed for the load and quality lamps/fixtures with good drivers. That combo solves most dimming issues.
What to look for (and what to avoid)
If you’re choosing products with dimming in mind, the biggest thing is to match the “language” of dimming: phase-cut / TRIAC / ELV / 0–10V / step dim / smart controls. Products that clearly state what they support are usually the ones that behave.
On the flip side, mixing random bulb brands on one dimmer is a common way to create a room full of inconsistent behavior. Also, don’t assume “LED dimmer” means “works with every LED.” It usually means “works with a lot more LEDs than older dimmers did.”
Quick FAQ: Dimming Problems
Why do my lights flicker when dimmed?
Most often it’s a dimmer + bulb/driver mismatch or a dimmer that can’t handle low LED loads.
Fix: try a modern LED-rated dimmer, use one bulb brand/model per circuit, and avoid bargain bulbs/drivers if low-end dimming matters.
Why do my lights buzz?
Buzzing usually comes from phase-cut dimming noise making components vibrate (more common with cheaper drivers or older dimmers).
Fix: use a higher-quality dimmer (often quieter), choose better-quality lamps, and if it’s a transformer-based load, consider a dimmer designed for that type (often ELV-style).
Why do my lights “pop on” at 20–30% instead of starting smoothly?
That’s typically a minimum driver threshold — below a certain point the driver can’t regulate cleanly.
Fix: choose bulbs/fixtures advertised for deep dimming (lower minimum), and use a dimmer known to have good low-end control (sometimes with an adjustment).
Why do some bulbs dim nicely and others don’t on the same dimmer?
Different bulbs use different drivers, so “dimmable” doesn’t mean “same behavior.”
Fix: keep bulbs matched (same brand/model), and stick to lamps that list dimmer compatibility or have a reputation for smooth dimming.
Can I use my old wheel/knob dimmer with modern bulbs?
With incandescent/halogen: usually yes. With LED: it’s a gamble, especially if the dimmer expects higher wattage or is older leading-edge style.
Fix: if you want reliable LED dimming, swap to a modern LED-rated dimmer.
Do fluorescent lights dim on normal wall dimmers?
Generally no — they need dimming ballasts and the right control method.
Fix: confirm the fixture/ballast is actually dimming-rated (and what method: 0–10V, etc.) before expecting smooth dimming.
Are all LEDs dimmable?
No. Some are non-dimmable, and some are “dimmable” but behave poorly.
Fix: look for explicitly dimmable lamps, ideally with stated dimming type (TRIAC/ELV/0–10V) or a compatibility list.
What’s a “good dimmer”?
One that’s designed for your load type and can control low wattage smoothly and quietly. Look for: “LED-rated,” better low-end performance, and (ideally) published compatibility guidance. Pairing a good dimmer with quality bulbs is the fastest way to avoid headaches.
Why do incandescents get warmer when dimmed, but LEDs don’t?
Incandescent warms naturally as the filament cools. LEDs don’t shift that way unless engineered to.
Fix: if you want that cozy warm shift, look for dim-to-warm LED products.
Why do my LEDs shut off at low dim (or strobe near the bottom)?
That’s usually the driver falling below its stable operating range (or the dimmer not “latching” properly on a low load).
Fix: use a better LED-rated dimmer with strong low-end control, choose bulbs/fixtures rated for deep dimming, and keep the circuit’s lamps matched (same model). If it’s still touchy, the simplest remedy is raising the usable minimum (accepting that “1%” might really be “10%” on that setup).
Why do my lights look fine to my eyes but flicker on camera?
Cameras (especially phones) can “catch” flicker that your brain ignores, because of how the camera shutter and frame rate sample the light output.
Fix: use higher-quality lamps/drivers marketed as flicker-free / low flicker, avoid cheap drivers, and in problem installs consider a control method that’s typically steadier (often 0–10V in commercial setups). If you’re filming regularly, choose products known for camera-friendly performance.
Why do my LEDs flicker only when something else turns on (fridge, microwave, furnace, etc.)?
That’s usually a voltage dip or electrical noise on the line when a motor or heavy load kicks on. Incandescent filaments shrug it off, but some LED drivers react visibly.
Fix: try higher-quality bulbs/drivers (better filtering and tolerance), keep bulbs matched on the dimmer, and use a better LED-rated dimmer. If it’s persistent across multiple circuits, it can point to a broader wiring/load issue — at that point it’s worth having an electrician check for loose neutrals, overloaded circuits, or other power-quality problems.
If you’re trying to make a dimming setup behave (quiet, smooth, and low-end stable), tell us what you’re dimming and what dimmer you’ve got. Most of the time, we can spot the compatibility issue in about 30 seconds.
Buchanan Lighting