Rotary Dimmers by Forbes & Lomax — Invisible

The Invisible Plate Rotary Dimmer by Forbes & Lomax is a push-to-switch, rotate-to-dim lighting control on a transparent acrylic plate. The Invisible Lightswitch was inspired by the glass plates of the 1930s and is built so the wall finish appears to run behind the switch without interruption.

Established in 1987, Forbes & Lomax is a UK-based heritage electrical brand recognized by architects and designers for refined switch and outlet design.

• Can I order online? Yes, if your lights are standard dimmable LED, you know the gang count, and the plate is 4 gang or under. Standard means a line voltage bulb or fixture that dims on its own, with no driver, transformer or power supply in the run. If there is one, the module is chosen by that device rather than the fixture, so check Electrical & LED Compatibility below.
• What should I confirm? Junction box depth and how many circuits run to the location. Your electrician will know both.
• Who decorates the inner plate? You or your decorator, as part of the wall finish and before the acrylic top plate goes on. Allow for it in the schedule rather than at handover.
• When should I request a custom quote? Drivers, transformers, 0-10 V, 5 gang or more, or anything you are unsure about should be confirmed by our sales team in order to ensure compliance and compatibility. Please reach out to us at contact@cassonhardware.com.
• Can I install it myself? No. Line voltage, licensed electrician only.

Full specifications, module ratings and installation requirements are below.

Each unit ships with two plates, and the inner plate is the point of the system. Paper or paint it to match the wall and the finish appears to continue unbroken behind the switch. This work is done by you or your decorator, not the electrician.

• Inner plate: primed aluminium, supplied ready to be papered or painted.
• Wallpaper: the inner plate can be used as a template to cut a piece to fit.
• Over stone or tile: the inner plate can be faux painted to match the surrounding surface.
• Top plate: transparent acrylic with bevelled edges, secured without visible fixing screws. It goes on after the inner plate is decorated.
• Sequence: the inner plate is decorated as part of the wall finish and left to dry before the top plate is fitted. Allow for it in the schedule rather than at handover.

Selecting the Right Module

The module is set by what your fixture is and what drives it, not by wattage alone. Measure the total connected load on that dimmer, then select from the table.

• LED module: available to order online in every fittings finish.
• Specialty modules: incandescent, magnetic low voltage and 0-10 V are available in every finish by request. They are needed only when a specific fixture calls for one, so they are not sold online.
• Minimum load: no formal minimum is stated for the LED module, though Forbes & Lomax recommend at least 5 W. Below that the dimmer may not register that a fixture is connected.
• 0-10 V wiring: a current-sinking signal dimmer. It connects to lighting drives through a Lutron PP-DV power pack or equivalent relay, purchased separately. All connections must be Class 2 and the install requires additional wiring beyond a conventional dimmer.
• Magnetic low voltage: for magnetic transformers only, 600 VA maximum with a 50 W minimum load. Must not be used with solid-state electronic low voltage.
• Electronic low voltage: not supported. Forbes & Lomax do not make an ELV or reverse phase dimmer. Where a fixture requires one, a non-dimming toggle switch is the only option.

Dimming LED

Dimming LED is difficult across the whole lighting industry, not just this range. Compatibility can usually be predicted from a fixture's specification sheet, which is why we ask for it, but some trial and error is normal. Send your lighting schedule to contact@cassonhardware.com and we will review it with Forbes & Lomax.

• Guarantee: Forbes & Lomax cannot guarantee that every fixture labelled dimmable will dim satisfactorily on a TRIAC module. Performance depends on the make of fixture and the driver inside it.
• Minor flickering: even on a compatible fixture, some flickering can occur at the top or bottom of the range. Optimizing the dimming range resolves most of it.
• Bulb recommendation: for screw-in LED, Forbes & Lomax recommend Philips Ultra Definition. They dim smoothly to low levels and hold colour quality.
• Testing on site: where a fixture is unusual and you need certainty before committing to a full order, buy a single dimmer and test it in place.
• One lighting type per dimmer: recessed lights and a chandelier on the same dimmer will perform poorly even where each is individually compatible.

• Electrician: must be installed by a licensed electrician, in accordance with appropriate electrical codes and regulations.
• Wiring: supplied as 3-way, works as single pole or 3-way. All modules wire conventionally except 0-10 V.
• Circuit position: a rotary dimmer can be wired at only one position on a 3-way or 4-way circuit. Every other position must be a toggle or non-dimming rotary switch.
• Junction box depth: recessed at least 1/8" below the finished wall surface so the plate sits flat. Refer to the Junction Box Assembly Diagram below. Check existing boxes before ordering.
• Plate finishing: the inner plate is decorated and dry before the electrician arrives. Refer to Prepping the Plate for Installation above.
• Non-dimming: rotary switches are available where a rotary style is wanted but only push on/off is required.
• Optimizing: the dimmer selects the correct dimming mode automatically once connected. Set the minimum and maximum levels for your fixtures, then apply the Program Lock. On a compatible fixture this resolves most flickering. Changing the mode by hand is a last resort, after optimizing has been tried.
• Momentary switches: not line voltage. They work only with home automation systems including Lutron Homeworks, Crestron, Savant, Vantage and Control 4.
• Areas of application: light-duty commercial, residential.

Plates of 5 gang or more, and any circuit with a driver, transformer or 0-10 V dimming, are quoted by our sales team. Send the following to contact@cassonhardware.com and we will price it against your schedule.

• Fixture make and model for every light on the circuit
• Driver or transformer type, if there is one
• Total connected wattage per dimmer
• Number of switching positions on the circuit
• Gang count and what else shares the plate
• Fittings finish
• Wall finish behind the plate, and whether it is paper, paint, plaster, stone or tile
• Junction box depth on site

Plate Sizes

All plates are 4.53" (115 mm) high. The top plate is 3 mm acrylic and the inner plate is 1 mm primed aluminium.

Dimmers, toggle switches, push buttons and outlets can be mixed on the same plate. Multi-gang plates are supplied to accommodate as many devices as required. Contact us with your device schedule for a quote.

Device Dimensions

• Knob: Ø 0.79" (20 mm). One dimmer fits per gang of a standard junction box.

• Plate: transparent acrylic top plate with a primed aluminium inner plate.
• Housings: the switch, dimmer and outlet housings are the same as those used on the metal plate range. Only the plate differs.
• Fittings: the finish applies to the knob and screws. The plate itself carries no metal finish.
• Living finish: Unlacquered Polished Brass darkens and develops a patina with handling and exposure. This is intended and not a defect, and variation between pieces is normal.
• Lacquered finishes: Nickel Silver, Brushed Stainless Steel, Antique Bronze, Lacquered Brushed Brass and Matte Brass hold a consistent colour and will not change.
• Matte Brass: carries a baked lacquer coating that resists fingerprints.
• Care: wipe clean with a dry, non-abrasive microfiber cloth. Avoid chemical or alcohol-based cleaners.

Available Fittings Finishes

• Unlacquered Polished Brass
• Nickel Silver
• Brushed Stainless Steel
• Antique Bronze
• Lacquered Brushed Brass
• Matte Brass

Aged Brass is not offered on the Invisible range.

• Rotary dimmers: conform to UL 1472, certified to CSA C22.2 No. 184.

Review and ensure all certifications are applicable for your local code.

Product Sheets

• Rotary Dimmer Cut Sheet
• Plate Dimensions
• Forbes & Lomax Brochure

Module Documentation

• 120 W LED / 300 W Incandescent — Wiring Instructions
• 120 W LED — Optimization Instructions
• 120 W LED — Compatibility & Troubleshooting Tips
• 500 W Incandescent / Halogen — Installation Instructions
• 600 VA Magnetic Low Voltage — Installation Instructions
• 0-10 V — Installation Instructions

Installation & Assembly

• General Instructions for Electricians (Switches & Dimmers)
• Junction Box Assembly Diagram (Rotary Dimmer)
• Invisible Plate Installation Notes
• Circuitry Visual Aid
• Home Automation Integration

Care

• Plate Cleaning Guidelines
• Sustainability Statement