Installing a light dimmer: connection and adjustment

A light dimmer transforms the atmosphere of a room: you go from a bright light for working to a soft, dimmed light for the evening. It is also an ally for reducing your consumption. Yet its installation requires more attention than that of a standard switch, especially with LED bulbs, which are not all compatible. Here is how to choose and install a light dimmer safely.

Choosing the right dimmer

• A dimmer suited to your bulb type: LED, halogen, compact fluorescent or incandescent (LED models are specific)
• A sufficient nominal power: add up the power of all the lamps on the circuit and keep a 20% margin
• A flush or surface-mounted model depending on your recessed box (45 mm depth recommended)
• A dimmer with rotary control, wheel, touch or sensor control depending on your preference of use
• If your LEDs buzz or flicker, choose a specific LED dimmer with a minimum level adjustment function (dimming range)

LED compatibility: the crucial point

Not all LED bulbs are dimmable: check the "dimmable" mention or the presence of a dimmer symbol on the packaging. A non-dimmable LED connected to a dimmer risks flickering, buzzing or burning out prematurely. Also check the minimum power supported by your dimmer: some require a minimum load (often 10 to 20 W) which is not reached with a single 5 W LED. In that case, go for a low-consumption dimmer whose range extends down to 1 W.

The installation steps step by step

1. Switch off the circuit breaker for the relevant circuit and check the absence of voltage at the box with a non-contact tester
2. Remove the existing switch by unscrewing the plate and the mechanism, then photograph the wiring
3. Identify the incoming live and the lamp return: the dimmer is connected on the live, never on the neutral
4. Strip the conductors to 8 to 10 mm and connect them to the dimmer respecting the markings (L for the live, L1 or output for the lamp return)
5. Insert the dimmer into the recessed box carefully folding the wires without crushing them
6. Refit the finishing plate, restore the power and test the full dimming range
7. If the light flickers at minimum intensity, adjust the low-level setting provided on the dimmer with the small slider or the adjustment button

Can several dimmers be placed on the same circuit?

No, it is forbidden to place several dimmers in series on the same circuit: it causes erratic operation and can damage the dimmers. To control the same light from several points, install a main dimmer and standard two-way switches upstream, or use a dedicated remote control kit that works wirelessly. For a dimmed two-way setup, prefer models specially designed for this configuration, following the manufacturer's diagram scrupulously.

Dimmer and energy savings

A well-used dimmer reduces the electrical consumption of your lighting: lowering the intensity to 50% generally makes the consumption of an LED drop by 40 to 50%, in addition to extending the bulb's lifespan, which undergoes less thermal stress. Be careful however: the saving is only real with good quality dimmable lamps, and a low-end LED dimmer can consume more than it saves. For a living room or bedroom, place the dimmer at the entrance to the room, at the standard height of 1.20 m from the floor. If you want to control several lighting points, one dimmer per circuit is necessary, each with its own minimum load.

Fine adjustment and usage habits

After installation, most dimmers have a screw or a slider to adjust the minimum brightness level. Set it so that the lamp does not flicker at the lowest level, while remaining sufficiently dimmed to achieve a real dimmed effect. Some touch dimmers memorise the last level used when switched off: handy for finding your favourite atmosphere as soon as you switch on. Get into the habit of using full power only when you need it: systematically varying the intensity during the day prolongs the lifespan of LED bulbs and reduces your electricity bill.

The mistakes to avoid

• Connecting a non-LED-compatible dimmer to LED bulbs: flickering and risk of damage
• Installing a dimmer whose minimum power is higher than the circuit's load
• Forgetting to check the absence of voltage before touching the wires
• Placing several dimmers in series on the same circuit
• Using a dimmer in a box that is too shallow, a source of overheating

A well-chosen and correctly wired dimmer will give you years of comfort and energy savings. The essential thing is to check compatibility with your bulbs, work with the power off and respect the connection direction on the live wire. For connected lighting or lighting controlled from several points, an electrician will know how to size the solution suited to your installation.