Lighting an Interior: From the Brief to the Circuit Schedule

Lighting is specified in three separate documents: a layout, a fitting schedule and a circuit schedule. Skip the third and the first two never work as intended.

Most interiors are lit by a layout showing where the fittings go, with no document saying which fittings switch together, which dim, and what the control looks like on the wall. That omission is why so many well-equipped rooms have only two usable lighting conditions. This sequence runs from the brief to a circuit schedule, which is the document that turns a set of fittings into a lighting scheme.

Before stage one

You can start once the layout is settled and the furniture plan is drawn to scale, because lighting positions follow furniture rather than the geometry of the room. You also need the reflected ceiling plan in progress, since every ceiling fitting competes for space with air grilles, detectors and access panels. Starting earlier produces a layout that will be redrawn; starting later means the electrical first fix is already in the walls.

• Confirm the furniture plan, including where people will sit, read, cook, work and face when they enter each room.
• Establish the ceiling void depth available, since recessed fittings have a required depth that the void may not offer.
• Decide which rooms genuinely need more than one lighting condition, and which only ever need one.
• Check the electrical capacity and the space available at the distribution board before assuming circuits can be added.
• Agree who owns the reflected ceiling plan, because lighting positions have to be coordinated there rather than in isolation.

Stage 1: Write the lighting brief room by room

For each room, record the tasks that happen in it, the times of day it is used, who uses it and what it should feel like in each of those conditions. A kitchen needs bright, even light on the worktop and something far softer when the room is used in the evening. A majlis needs light that flatters faces across a seating arrangement rather than light aimed at the floor. A bedroom needs a condition for dressing and a condition for reading without waking a partner. Writing this down produces a requirement that can be designed against, where a style reference cannot.

• Deliverable: A written lighting brief per room listing tasks, times of use, required conditions and any constraint.
• Owner: Designer drafts; owner confirms against how the household actually lives.
• Approval gate: Every room has a stated number of lighting conditions before any fitting is selected.

Stage 2: Design the layers before choosing fittings

Decide what each layer of light in the room is doing. Ambient light fills the volume and keeps contrast comfortable. Task light serves an activity at a specific surface. Accent light picks out a material, an object or a plane. Decorative fittings are themselves objects to be seen. Working in layers prevents the most common failure, which is a grid of identical downlights asked to do all four jobs at once and succeeding at none. Position the layers against the furniture: task light over the actual worktop and reading position, accent light on the actual wall that will carry something.

• Deliverable: A layered lighting intent drawing per room, showing which layer each light position belongs to.
• Owner: Designer leads; services engineer reviews feasibility.
• Approval gate: Each light position is assigned to a layer and a purpose, with no position left unexplained.

Stage 3: Select fittings and fix the light quality

Only now choose products, and choose them on performance before appearance: output, beam distribution, colour temperature, colour rendering, glare control and the depth they need above the ceiling. Keep the colour temperature consistent within a space and consistent in equivalent spaces, because a mixture reads as a mistake even when each fitting is good. Confirm dimming compatibility between the fitting, its driver and the intended control system at this stage rather than at commissioning, since incompatibility shows up as flicker or a limited dimming range that cannot be fixed afterwards.

• Deliverable: A fitting schedule with manufacturer, reference, output, beam angle, colour temperature, colour rendering and driver type.
• Owner: Designer specifies; electrical contractor confirms compatibility in writing.
• Approval gate: Dimming compatibility is confirmed for every dimmed fitting before anything is ordered.

Stage 4: Coordinate every position on the ceiling plan

Transfer the lighting positions onto the coordinated reflected ceiling plan and resolve them against the air grilles, detectors, sprinklers where present, speakers and access panels. This is where positions move, and it is far better that they move on paper. Check that recessed fittings have the void depth they need at their actual positions rather than at the deepest point of the ceiling, and that no fitting sits where a duct or a structural beam makes installation impossible.

• Deliverable: A coordinated reflected ceiling plan with every lighting position dimensioned and clash-free.
• Owner: The party holding ceiling coordination; designer confirms the design intent survives.
• Approval gate: No lighting position is installed before it appears on the coordinated plan.

Stage 5: Write the circuit schedule

This is the document almost everyone omits. For each room, list the circuits, state which fittings sit on each one, whether the circuit dims, and which switch or control position operates it. Then describe the conditions you want: in a kitchen, perhaps worktop task light alone, worktop plus ambient, and a low evening setting. If those conditions cannot be produced by the circuits listed, the circuits are wrong, and this is the moment to fix it. A room with eight fittings on one circuit has one condition no matter how good the fittings are.

• Deliverable: A circuit schedule per room naming each circuit, its fittings, its dimming status and its control position.
• Owner: Designer writes; electrical contractor prices and confirms board capacity.
• Approval gate: Each stated lighting condition in the brief is demonstrably achievable from the listed circuits.

Stage 6: Set out the control positions and label them

Decide where the switches and control plates go, from the user's point of view rather than the electrician's. A plate behind a door swing, on the wrong side of an entrance, or in a position that forces someone to cross a dark room is a daily irritation that cannot be moved later without cutting into finished plaster. Keep the number of plates low and the logic consistent between rooms. Agree the labelling or engraving at this stage, because a plate with six unmarked buttons is used as a plate with one.

• Deliverable: A switch and control position plan with plate types, gang counts and the engraving or labelling for each.
• Owner: Designer positions; owner approves by standing in the space where possible.
• Approval gate: Positions marked on the wall in tape and approved before electrical first fix is closed.

Stage 7: Commission, adjust and record

Lighting is the one interior element that must be commissioned at night, with the furniture and the window treatments in place. Aim every adjustable fitting, set the dimming levels for each stated condition, and check for glare from every seating position rather than from the middle of the room. Record the settings, the fitting references, the driver types and the control programming, because an unrecorded scene setting is lost the first time the system is reset or a driver is replaced.

• Deliverable: A commissioning record with aiming, dimming levels per scene, fitting references and control programming.
• Owner: Contractor commissions; designer attends; owner signs off at night.
• Approval gate: Final payment released only after a night-time commissioning walk-through is accepted.

Handovers between stages

The weak hand-off is between the lighting designer and the electrical contractor, because a layout can be installed faithfully and still produce the wrong result if the circuiting was never specified. Close it by making the circuit schedule a contract document and requiring the contractor to confirm board capacity against it before the first cable is pulled. The second weak point is between the fitting supplier and the control supplier, where dimming incompatibility hides until commissioning. Require a written compatibility statement naming the fitting, the driver and the control device.

How you know it is finished

The lighting is complete when every condition in the brief can be produced from a labelled control, when no fitting glares into a seating position, and when the commissioning record would let someone restore the settings after a component is replaced. Requirements for electrical installation, testing and energy performance are revised from time to time, so confirm the current position with the relevant authority and a qualified electrical engineer when you install rather than relying on a previous project. Where a lighting installation forms part of a life safety provision such as escape lighting, have the design and the testing confirmed by a qualified engineer against the applicable civil defence requirements.

Domira designs and delivers interiors as part of the building, not after it: the finishing schedule, the joinery and the services coordination that decide whether a space looks built or assembled. Share the space and Domira will tell you what it would specify and what it would leave out.