Dimmable LED bulbs: How do they work?

What is a dimmable light bulb?

A dimmable LED bulb, also known as a dimmable light bulb, contains an electronic driver capable of interpreting a dimming signal to adjust the luminous flux. Unlike a standard LED, which operates at full power, it adjusts its brightness based on the command it receives. Our Guide to LED Bulbs and Spotlights lists these models along with their technical specifications.

The Principle of Variable Lighting

The dimmable feature relies on the internal driver's ability to modulate the current supplied to the LEDs. To understand how this technology actually works, keep this simple point in mind: the drive controls a change in current within this flux range, without ever altering the supply voltage. The driver processes the signal sent by the inverter differently, then reduces or increases the current supplied to the diodes.

• PWM Modulation : The driver turns the LEDs on and off at a high frequency. The eye then perceives a variation in intensity without any noticeable flicker.
• Analog dimming : The current or voltage supplying the LEDs gradually decreases, producing a smooth transition in brightness.
• Dimming range : Most dimmable bulbs can be dimmed down to 10% of their maximum light output, whereas a non-dimmable model turns off abruptly.

The benefits are tangible: electricity consumption decreases as the brightness is lowered, the ambiance adapts to the activity, and the bulb's lifespan can be extended when it operates at reduced brightness. Some models have a rated operating life of up to 15,000 hours; moderate use can further extend their lifespan.

Dimmable or non-dimmable

Check the certification before purchasing. The information on the packaging eliminates the need to open the base to identify the driver type. In Europe, the words "dimmable" or "non-dimmable" have been required to appear on packaging since 2018.

A non-dimmable light bulb cannot be modified to become dimmable: its circuitry is not designed for that purpose. In a circuit that is already equipped with a variable-speed drive, replacing it with a dimmable model prevents this damage to the control circuit. The difference lies in whether the driver is compatible with dimming signals.

Check the instructions on the packaging or the manufacturer's technical data sheet before installation. For an existing light fixture controlled by a dimmer, you must replace a non-dimmable bulb with a compatible model and use a suitable dimmer: this way, you preserve the circuit and enjoy stable dimming.

How Does an LED Dimmer Work?

The dimmer is the key component that controls the current sent to the light bulb. It replaces a conventional switch in the lighting circuit and regulates the power supplied to the bulb's driver. Without a dedicated device, it’s impossible to adjust the brightness of a dimmable LED: it simply turns on at full power, just like a regular light bulb.

A light bulb works without a dimmer switch

A dimmable LED bulb works on a standard circuit without a dimmer: it turns on and off normally, at full power. To take advantage of its dimming capability, install a compatible dimmable LED dimmer in place of the existing switch. This wall-mounted device regulates the signal sent to the driver to control the brightness of the light bulb.

• Rotary knob : It allows for continuous and intuitive adjustment of the light intensity, from minimum to maximum, with a single gesture.
• Multi-level push button : Three or four preset brightness levels are activated by successive presses. This solution is appropriate when adjustment accuracy is not a priority.
• Touch control : Press and hold or swipe the surface to adjust the intensity. This control is often integrated into modern home automation systems.

Once the dimmer is installed, the light bulb receives a modulated signal rather than a constant power supply. The driver interprets this signal and adjusts the current sent to the diodes in real time. In practice, you can switch from bright task lighting to soft lighting for an evening without replacing the light bulb or modifying the circuit.

Dimming signals

TRIAC technology is widely used in French 230-volt residential installations. The component cuts off each half-wave of the alternating current; the timing of the cut-off then determines the amount of energy delivered to the light bulb. A falling-edge dimmer is generally better suited to the low power levels of modern LEDs than an older rising-edge model designed for halogen bulbs: it reduces the risk of flickering and overheating. Conversely, an older halogen dimmer can cause the light to flicker or go out abruptly before the brightness reaches zero.

A dimmable light bulb can operate without a dimmer, but its dimming capability remains unused in that case: it behaves like a standard LED. The PWM, 0–10 V, 1–10 V, DALI, and DMX protocols are reserved for integrated lighting systems, LED strips, and more complex home automation systems. For everyday residential use, TRIAC dimming is sufficient in the vast majority of situations.

Applications for Low-Voltage LEDs

Low-voltage LED bulbs and spotlights operating at 12 V or 24 V—such as those with GU5.3, GU4, or G4 bases—require a different installation process than that of a standard 230 V bulb. The dimmer alone is not enough: a dimmer-compatible transformer must be installed between the dimmer and the light bulbs. The manufacturer must specify that this transformer is dimmable or TRIAC-compatible so that the dimming signal is converted correctly.

• TRIAC dimmer : Installed upstream of the power supply on the 230 V mains, it modulates the signal before it is converted to variable low voltage.
• Variable power supply : Labeled “dimmable” or “TRIAC” by the manufacturer, it converts the input TRIAC signal into an output PWM signal suitable for LEDs.
• Electronic ballast : It must support dimming. A standard model that is not compatible may cause flickering or prevent any changes.
• Dimmable GU10 LEDs : These spotlights operate directly at 230 V and do not require a transformer. However, their variable-speed drive must remain compatible with the total connected load.

Depending on the setup of the housing, it may be necessary to replace both the power supply and the dimmer to achieve stable dimming. Before ordering any equipment, verify that the transformer is compatible with the selected drive. The difference lies in the overall compatibility: the bulb, voltage, wattage, dimmer, and power supply must all work together.

Choose a compatible dimmable light bulb

The word “dimmable” on the packaging is a good first indicator. However, it is not enough to ensure that the system operates properly. Compatibility between the light bulb, the dimmer, and the existing electrical circuit is determined based on several technical criteria: an ill-considered choice can cause dimming issues, even with new equipment.

Check compatibility with the drive

A dimmer must explicitly state that it is compatible with LEDs and that its power range matches that of the connected bulbs. An 8.8-watt dimmable E27 LED bulb, such as the LED Classic PFM CLA60 Frosted Dimmable E27 8.8 W 806 lm, therefore requires a dimmer whose minimum and maximum load ranges fall within this wattage. The difference lies in the combination of these two elements, which are often the source of gradation problems.

• Minimum load for the dimmer : A model that requires a minimum of 20 W will not function properly with a single 4 W LED bulb. The lights may flicker or turn off unexpectedly.
• Maximum load of the dimmer : The total wattage of the light bulbs connected to the same circuit must not exceed the specified capacity. A margin of 10 to 15 percent is still recommended.
• Declared load type : The drive must specify its compatibility with LEDs. A fixture designed exclusively for halogen bulbs will cause an LED to sizzle as soon as it is turned on.
• Circuit consistency : Using the same bulb model in a circuit minimizes performance variations between drivers of different generations or technologies.

The light bulb's technical specifications may also list dimmers that have been tested and approved by the manufacturer. Check this list before making a purchase: doing so reduces the risk of having to replace equipment after installation.

Avoiding Gradation Errors

Certain symptoms indicate that the light bulb and the dimmer are incompatible. Flickering often occurs when the minimum load is not met or when the type of load is not compatible with the technology being used. A buzzing sound may indicate that the dimmer is causing components in the LED driver to vibrate, while the light turning off before reaching the minimum brightness level generally indicates that the dimming signal is no longer being maintained properly.

A residual glow—visible when the light bulb remains dimly lit at the lowest setting—is often caused by a leakage current or by an electrical system that lacks a neutral wire. If these symptoms persist, consider using a next-generation electronic dimmer capable of handling low power levels. It will be better suited for modern LED drivers. Simply replacing the light bulb won't be enough if the dimmer switch isn't compatible.

Choosing the Right Base and Luminous Flux

The base determines mechanical compatibility with the light fixture. Check the light fixture's manual to identify the exact base type before placing an order. Check which type of light bulb is compatible before looking at the luminous flux: this quick step will help you avoid ordering the wrong one.

Measured in lumens, luminous flux determines the perceived brightness in a room. At the same wattage, a dimmable LED can provide a light output comparable to that of a more powerful incandescent bulb, while consuming less electricity. In a living room or bedroom, a light output of 806 lm at 8.8 W—such as that of the LED Classic PFM CLA60—provides comfortable lighting at full power and allows you to adjust the brightness to suit the desired atmosphere.

Color temperature rounds out the selection: 2,700 K produces a warm, soothing light for living spaces, while 4,000 K offers a neutral light suitable for an office or workshop. Wattage, luminous flux, and color temperature also help control energy consumption over time. Depending on the layout of the room, these criteria guide the selection of a dimmable E27 LED bulb and determine the quality of the lighting produced.