Your lights cost you £96 a year: can a £22 dimmer replace two switches and save 20–30% this week?

As darker evenings creep in, a quiet shift in British homes is gathering pace, and it starts at the wall.

Householders are reaching for a small, low-cost device to change the feel of rooms and to tame energy use. The trend is simple: trade a two-gang switch for a dimmer and set the mood from cosy to bright in seconds.

Dark evenings, brighter ideas

Retailers report brisk autumn demand for dimmer modules, while electricians say calls for quick lighting refreshes rise as clocks change. People want softer rooms, cheaper lighting, and less glare. Many also face a practical question: can a dimmer safely replace a double switch without rewiring the house?

Switch off at the consumer unit and verify dead before touching any conductor. Safe isolation stops shocks.

The short answer is yes, but the right choice of dimmer and a calm, labelled approach to wiring matter. You also need to decide whether you want one dimmer to control a single circuit, or a two-gang dimmer to keep independent control of two separate lighting runs.

Can you swap a two-gang switch for a dimmer?

A standard two-gang switch usually controls two separate lighting circuits in the same room, like ceiling spots and a pendant. Replacing it gives you three routes:

• Use a two-gang dimmer to keep separate control and dim both circuits.
• Fit a one-gang dimmer and cap off the unused switched live, leaving the second circuit permanently disconnected or later moved to another switch.
• Move one circuit to a smart bulb or smart relay and keep a single-gang dimmer for the main lights.

Never join two different circuits onto one dimmer. They must share the same feed and protective device if you plan to control them together. If in doubt, call a qualified electrician.

Do not tie two breakers to one dimmer. One protective device, one circuit, one control point.

What you need before you start

• Trailing-edge dimmer rated for LEDs (typical LED range 5–120 W, check the packaging).
• 2-gang version if you need to control two circuits independently.
• Screwdrivers (flat and cross-head), insulated pliers, voltage tester, labels or masking tape, fine marker.
• Optional: smartphone for clear photos of the original wiring.

Step-by-step at a glance

• Isolate at the consumer unit. Confirm dead with a two-pole tester.
• Remove the faceplate. Photograph the wiring. Label each conductor: feed (common), switched lives, earth, and any link straps.
• Note colours: in modern UK wiring brown = live, blue = neutral, green/yellow = earth. Many switch drops carry live and switched live only.
• Transfer conductors to the dimmer terminals: common (C) for the feed, L1 for the switched live on each gang. Earth to the back box if metal.
• Mount the dimmer square and secure. Restore power. Test at low and high levels for smooth dimming and no flicker.

Use dimmable LED lamps and a trailing-edge dimmer. A mismatch causes flicker, buzz and heat.

Choosing the right dimmer

Modern dimmers fall into three broad groups. Pick one that matches your lamps and the way you use the room.

Compatibility and the LED problem

Not all LEDs dim. Look for a dimmable icon on the lamp box. A non-dimmable lamp will flicker or cut out on a dimmer and may fail early. Even with dimmable lamps, performance varies by brand and driver quality. Many makers publish compatibility lists for their dimmers and bulbs.

Minimum load matters. A dimmer rated 5–120 W (LED) might misbehave with a single 4 W lamp. Pair fixtures or pick a dimmer with a lower minimum. Some smart dimmers include a “calibration” mode that learns your lamp’s behaviour and smooths the low end.

Neutral at the switch position can be absent in older homes. Most retrofit trailing-edge dimmers do not need a neutral, which helps. Smart modules often do. If your box lacks a neutral, look for a neutral-less smart dimmer or consult an electrician about safe options.

What savings can you expect?

Lighting typically accounts for about 10–15% of a home’s electricity use. A dimmer reduces lamp power when you turn the level down. The saving depends on lamp type and the drivers behind the LEDs.

• Six 8 W LED spots (48 W total) dimmed to a comfortable evening level near 60% brightness may draw around 28–35 W.
• Used three hours nightly, that can trim 20–25 kWh per year, worth roughly £5–£7 at 25–30 p/kWh.
• With halogens, cuts are larger because the relationship between dim level and wattage is closer to linear. Savings of £15–£30 per room are possible if you regularly dim.
• Lower stress on LEDs can extend lifespan and reduce replacements. That reduces waste and trips to the shops.

The bigger win is comfort. Lower levels reduce eye strain at night, improve TV viewing, and set a calmer tone for winding down. Many households value that as much as the pounds shaved from bills.

Common pitfalls and quick fixes

• Flicker at low levels: try a different dimmer profile, raise the minimum trim if your model allows, or choose lamps from the manufacturer’s compatibility list.
• Buzzing plate or lamps: switch to a trailing-edge dimmer and ensure secure terminations. Loose screws vibrate.
• Dead spots on the dial: some LEDs jump from off to bright. A better-quality lamp or a smart dimmer with calibration usually smooths the curve.
• Two-way circuits: for stairs or rooms with two control points, use a dimmer designed for two-way operation and pair it with an appropriate secondary switch or slave module.

Safety and small-print you should know

Replacement of a like-for-like accessory in most English homes is generally not notifiable work, but bathrooms and special locations carry extra rules. Follow Part P guidance, keep the circuit isolated, and use the correct protective device. A metal faceplate needs an earth tail to the back box. If anything looks unusual behind the switch, stop and get a professional in.

Label every conductor before you disconnect it. A clear photo and two labels save a long evening later.

Smart add-ons and future-proofing

If you want scenes and schedules, pair a trailing-edge dimmer with dimmable bulbs from the same brand family, or choose a smart module that supports Matter, Zigbee or Z-Wave. Many smart dimmers need a 35 mm or deeper back box and, often, a neutral. Some include press-to-dim toggles that act like standard switches for guests.

You can also mix layers: keep a dimmer for the main circuit, add a plug-in smart lamp for accent light, and store two or three preset levels you use every night. That combination often gives the best blend of comfort and control without a full rewiring job.

A quick decision guide for your room

• Kitchen with spots on two circuits: fit a two-gang trailing-edge dimmer rated 2 × 5–120 W (LED).
• Lounge pendant with LED filament lamps: choose a premium trailing-edge dimmer with adjustable minimum level.
• Nursery night routine: use a dimmer with soft-start and a wide low end to avoid sudden jumps in brightness.
• Hall two-way switching: select a dimmer compatible with two-way wiring and pair it with a retractive or designated slave switch.

Final notes to widen your options

If your existing box is shallow, a low-profile dimmer or a deeper back box spacer solves tight fits. For very low loads, an inline bypass across the lamp may stabilise flicker, but only use a device approved by the dimmer maker. Consider colour temperature as part of mood: warm white (2,700–3,000 K) reads calmer; neutral white sharpens task areas. A ten-minute test with different bulbs in one fitting often tells you more than a spec sheet.

For households on a budget, start with one busy room. Time the swap for daylight, label as you go, and keep the old switch. If you later switch to smart control, you can refit the classic plate or move the dimmer to another room. Small changes at the wall can shape how the whole home feels after dark.