Smart bulbs or smart wall switches for home lighting, and why does the neutral wire matter?

The basic difference is where the intelligence sits. A smart bulb needs permanent power to stay on the network, so the wall switch must stay on; the moment someone uses the switch out of habit, the bulb is offline and automations stop. A smart switch or an in-wall relay keeps ordinary lamps and keeps the wall control working the way people expect, which is usually the deciding point in a shared household.

Bulbs win when you want colour or tunable white, or when you cannot touch the wiring, as in rented property. Switches win when one switch feeds several lamps: one device instead of six bulbs, and replacement lamps stay cheap.

The neutral issue is about how the switch powers its own electronics. A traditional switch box often has only the live feed and the switched wire to the lamp; the neutral goes to the lamp directly. A smart switch needs a small continuous supply for its radio and relay driver. With a neutral in the box it simply connects across live and neutral. Without one, a no-neutral switch has to pass a small current through the lamp even when the lamp is off.

That worked with filament lamps, which look like a low resistance when cold. An LED lamp draws very little: a 5 W lamp at 230 V takes only about 22 mA when fully on, so a standby current of a milliamp or two is enough to charge its driver and make it glow faintly or flash. The usual cure is a bypass module fitted across the lamp, supplied or specified by the switch maker.

Check load type and ratings as carefully as the wiring. LED drivers have a high inrush current, and relay contacts are rated differently for LED or capacitive loads than for resistive ones, so look for the LED rating in the datasheet, not just the headline amps. For dimming, the lamp must be marked dimmable and the dimmer type must suit it: many LED lamps behave better on trailing-edge dimmers than on older leading-edge triac dimmers, and most dimmers have a minimum load below which they flicker.

Never put a smart bulb on a dimmer circuit, smart or not. The bulb has its own driver and expects the full supply voltage.

There is a useful third option if you like smart bulbs but want working wall controls: a relay module or smart switch that supports a detached (decoupled) mode. The wall switch no longer cuts the power; it just reports a button press to the controller, which then commands the bulbs. The relay keeps the bulbs powered and, depending on the device, can still switch them directly as a fallback if the controller is down.

Battery-powered wireless wall remotes achieve much the same without touching the wiring: leave the original switch on, fit a cover over it, and mount the remote beside it.

On the practical side, this is fixed mains wiring. Switch off the circuit at the distribution board and prove it is dead with a tester before opening a switch box, and do not assume that wire colours tell you which conductor is which in an older installation. In many countries this work must be done or checked by a qualified electrician, and in-wall devices should carry the approvals required where you live.

Also check the depth of the wall box before buying in-wall modules. A relay module plus the existing wiring needs space, and a module crammed behind a switch with strained conductors is both unreliable and unsafe. If the box has no neutral and is shallow, smart bulbs with a wireless remote are often the most sensible answer.