Lighting Specification Basics for Interior Designers

A lighting specification is the written record of what light a space must deliver and which fittings, sources and controls will deliver it. For a London project, the basics are: set the task and the mood for each room, check the quantitative targets against the SLL Code for Lighting, choose fittings and sources to meet them, define the controls, and write it all into a schedule a contractor can price and install without guessing.

This guide walks through that sequence in the order you would work on a live scheme. It is written for interior designers, architects and contractors, not for homeowners.

TL;DR

• Specify the light you need (task, level, colour, control) before you choose the fitting.
• Lux is only the starting point. Glare, uniformity and colour rendering decide whether a room feels right.
• Use the SLL Code for Lighting for quantitative targets, and treat daylight as part of the scheme.
• Plan emergency lighting and controls at layout stage, not at handover.
• A good schedule names the product, finish, source, driver, dimming protocol and mounting detail for every item.

Table of Contents

• What a lighting specification actually contains
• Start with the brief, not the catalogue
• Reading lux, and why it is not enough
• Use the SLL Code for Lighting properly
• Daylight comes first
• Controls: decide them at layout stage
• Emergency lighting and compliance
• Writing the schedule
• Decorative and architectural light together
• A short pre-issue checklist
• Our view: specify the light, then the fitting
• Specifying lighting with a working London base
• FAQ
• Sources

What a lighting specification actually contains

A specification is not a list of nice fittings. It has two layers.

The first is the performance brief: what each space has to do. A kitchen island needs bright, even, glare-free light for food preparation. A dining room needs low-level, warm, dimmable light that flatters people and tableware. A gallery wall needs controlled accent light with good colour rendering.

The second is the product schedule: the fittings, lamps or integrated LED modules, drivers, controls and accessories that deliver the brief. Each line should be unambiguous enough that a substitute can be judged against it.

RICS procurement guidance on service specifications describes three ways to frame requirements, and the logic carries over neatly to lighting, as input, output or outcome specifications:

• Input: you state exactly what is installed (this luminaire, this driver).
• Output: you state what the lighting must achieve (a maintained illuminance, a glare limit).
• Outcome: you state the environment you want (a calm, residential-feeling workspace).

The guidance notes that output-based approaches leave room for innovation and energy-saving technology but need clearer performance targets. On most interior projects a hybrid works best: outcome and output statements for the room, input detail for the visible, designed fittings.

Start with the brief, not the catalogue

Before opening a product book, write a short brief for each room. Cover:

1. Tasks: what happens here, and at what time of day?
2. Users: age, eyesight, working hours. Older occupants generally need more light on the task.
3. Surfaces: dark stone, lacquer and mirror behave very differently from matt plaster and pale oak.
4. Daylight: orientation, window size and any London-specific constraints such as a lightwell or a north-facing mews elevation.
5. Layers: ambient, task, accent and decorative light, and which switching group each belongs to.
6. Existing infrastructure: ceiling void depth, joist direction, whether a listed building limits where you can cut.

The void depth question alone eliminates a surprising number of recessed fittings. Check it before you fall for a product.

Reading lux, and why it is not enough

Illuminance, measured in lux, is the light arriving on a surface. It is the figure most people quote first, and the SLL Code for Lighting is where UK practitioners look for recommended values. CIBSE’s lighting top tips point to the Code for quantitative requirements, with typical task illuminances ranging from roughly 100 to 1000 lux depending on the task.

The same guidance sets out the principles that make a scheme work beyond the number:

• Provide the recommended illuminance on the task.
• Keep the distribution on the task uniform.
• Keep the surrounding area similar in level to the task area.
• Avoid confusing shadows and disturbing glare.

In practice, a room that hits its lux target can still feel harsh if a bright downlight sits in the eyeline, or dull if the walls are left dark. Look at luminance (what the eye sees as brightness on surfaces) as well as illuminance.

Glare

Discomfort glare usually comes from excessive brightness contrast, such as a bare high-output source against a dark ceiling. In offices and home offices, the CIBSE guidance recommends managing it through glare control, uniformity and colour rendering alongside illuminance. Specify deep-set or baffled downlights, and consider the position of screens relative to windows and fittings.

Colour temperature and colour rendering

Two figures belong on every schedule line:

• Colour temperature (CCT, in kelvin): warm white for living and hospitality spaces, neutral for kitchens and workspaces. Mixing CCTs within one sightline is the most common visible mistake.
• Colour rendering (CRI or, increasingly, more detailed metrics): how faithfully the source shows colour. For rooms with fabrics, art, skin tones and timber, ask for a high-quality source and check the manufacturer’s data sheet rather than assuming.

Also state the binning or tolerance if you are using several fittings in one room, so a batch variation does not leave one wall noticeably cooler than the next.

Flicker

Choose flicker-free sources and compatible drivers, particularly for workspaces. CIBSE’s guidance specifically points to flicker-free sources as good practice for modern offices and home offices. Flicker also shows on camera, which matters for studio and content spaces.

Use the SLL Code for Lighting properly

The SLL Code for Lighting is the main UK reference for the fundamentals of applying light in the built environment. CIBSE explains that the Code was once the de facto UK standard before European standardisation took over the recommendations, and that the 2022 edition updates it for rapid development in lighting technology.

Its role has shifted. It now works as a guide to interpreting the British and European standards, and CIBSE describes how practitioners use it to understand the calculations behind software results. That matters for designers: if you are relying on a manufacturer’s layout software or a lighting consultant’s calculation, you should know enough to question the input assumptions, such as reflectances, maintenance factor and working plane height.

For larger or more complex spaces, bring in a lighting designer or engineer early. The basics here help you brief them well and review what they return.

Daylight comes first

CIBSE’s advice is that well-controlled daylight should be the first consideration in a lighting scheme, because it gives comfort and colour rendering at no running cost. In the specification, that means:

• Locate task areas with daylight in mind, then add artificial light to fill the gaps.
• Zone the circuits so rows nearest the windows can be dimmed or switched separately.
• Consider daylight-linked dimming where the room is used for long periods.

Add blinds or curtains to your thinking. A scheme that glares at 4 pm because the sun hits a polished floor was not specified for daylight.

Controls: decide them at layout stage

Controls are where many schemes fall apart. The fitting is chosen, the ceiling is closed, and only then does someone ask how it dims.

A control specification should state:

• Dimming protocol: for example phase-cut, 0-10V, DALI or a wireless system. The driver in the fitting must match the control.
• Scenes and zones: which fittings group together, and what each scene should do.
• Sensors: occupancy and daylight sensors, if used, and where they sit.
• Keypads and interfaces: location, finish and mounting height, coordinated with the joinery and electrical drawings.

CIBSE’s top tips note that sensors and controls can cut energy use, but they need to be planned into the initial layout to work. Take any percentage savings you see quoted with caution, and check them against the source for your building type.

Also ask about maintenance. A defined maintenance factor in the design calculation allows for the fact that LED output declines over time, so a scheme does not fall short of its target a few years in.

Emergency lighting and compliance

This is where interiors for commercial, hospitality and common-part projects differ most from private residential work.

Emergency lighting in non-domestic buildings in the UK is governed by BS 5266, and Designing Buildings summarises the key points: fittings provide illumination for safe evacuation during a mains failure, and are either non-maintained (lit only on power failure, such as many exit signs) or maintained (on continuously). The same page gives a minimum of 1 lux along escape routes.

What that means for your specification:

• Coordinate the emergency layout with the fire strategy and the building control officer. Do not design it from a web page.
• Maintained emergency fittings can form part of your visible scheme, so choose them as deliberately as any other fitting.
• Emergency luminaires may operate at reduced output on battery, so confirm the product data.
• A change of use, a new partition or a lowered ceiling can alter the emergency requirements. Have the fire engineer or electrical designer review the revised layout.

Emergency lighting is a regulatory matter for workplaces, and not generally for single private dwellings, but houses in multiple occupation and common areas of residential blocks are different. Confirm the position with your building control body or a fire safety adviser for the specific building.

Energy rules

Lighting also falls within the energy provisions of Building Regulations. The government’s Approved Documents cover dwellings (Volume 1) and buildings other than dwellings (Volume 2). Volume 1 requires the efficacy of light sources in fixed lighting to be accounted for in the energy calculations. The thresholds and control requirements differ between the two volumes and between new work and alterations, so read the current edition for your project type, and check with your Part L assessor or building control before you finalise fittings. The same applies to any planning or Part L implications for conversions; our note on studio versus home office specifications covers the trade-side detail.

Writing the schedule

A lighting schedule should let someone else buy exactly what you intended. For each line include:

Two habits save a lot of trouble. First, give every fitting a reference on the plan and make sure the schedule and the drawing match. Second, state clearly whether alternatives are acceptable and on what basis. Our guide to FF&E specification writing sets out how to word these clauses across a whole project, and the FF&E lead times note explains why a lighting order should be scheduled backwards from the install date, because drivers, finishes and custom pieces often set the critical path.

Decorative and architectural light together

Most residential and hospitality schemes combine two families of fitting:

• Architectural lighting: recessed, track, linear and wall-wash fittings that shape the room quietly. These carry most of the technical specification, such as beam angle, glare control and dimming.
• Decorative lighting: pendants, wall lights, table and floor lamps that give the room character. These carry more of the design intent, such as finish, scale and height above table.

Specify them together. A chandelier with exposed lamps sets the glare profile of a dining room, and a statement pendant over an island may need a dedicated circuit and a ceiling fixing detail agreed with the contractor before the plasterboard goes up.

It also helps to see the real thing. Beam spread, finish and the warmth of a source on stone or timber are hard to judge from a data sheet. Faura’s lighting showroom in London lets trade visitors see decorative and architectural lighting in finished interiors, and brand pages such as Delta Light, Flexalighting and CTO Lighting show what is represented.

A short pre-issue checklist

Before a lighting package goes to the contractor or into a tender, check that:

1. Every room has a stated brief and layers of light.
2. Targets have been checked against the SLL Code for Lighting or against the consultant’s calculation.
3. Glare, uniformity and colour rendering are covered, not just lux.
4. CCT is consistent within each sightline.
5. Drivers and controls are compatible and the dimming protocol is stated.
6. Emergency lighting has been reviewed by the person responsible for the fire strategy.
7. Ceiling voids, cut-outs and fixings are coordinated with joinery and services.
8. Part L compliance has been confirmed for the project type.
9. Lead times are known for every fitting, including finishes and custom items.
10. The schedule matches the drawing line for line.

Our view: specify the light, then the fitting

We see the same pattern in projects that arrive for specification: the fitting is chosen first because it photographs well, and the light is worked out afterwards. It is usually easier the other way round. Decide what each room must do, set the controls, then pick the fittings that deliver it and look right.

For London projects, that discipline matters more because the buildings are so varied: shallow ceiling voids in period conversions, deep service zones in new-build apartments, and strict constraints in listed properties. Seeing fittings in a finished room, checking finish samples against stone and timber, and having technical files to hand at the same time shortens the path from concept to a schedule you can issue with confidence.

We built the Faura residency around that way of working: finished interiors on two floors, over 200 brands, samples and technical files in one place, and a team that can handle procurement, logistics and delivery for the whole order.

— Faura Editorial

Specifying lighting with a working London base

Faura is a trade-only showroom and residency in Westminster for interior designers, architects, developers and contractors. Visits are by appointment, Monday to Friday, 09:00 to 18:00. If you are specifying a scheme, you can review lighting alongside furniture, surfaces and hardware, present it to your client in the showroom, and pass procurement to one team. Trade terms are agreed individually with each approved trade account.

See how the residency for interior designers works, or explore trade access to apply for an account. Architects and developers can read about specification support and FF&E procurement.

FAQ

What is the difference between lux and lumens?

Lumens measure the total light a source emits. Lux measures how much of that light lands on a surface, per square metre. A fitting’s lumen output tells you little about a room until you know beam angle, mounting height and surface reflectance, which is why calculations matter.

Do I need emergency lighting in a residential project?

It depends on the building. Emergency lighting under BS 5266 applies to non-domestic premises, and is not generally required inside a single private dwelling. Common areas, HMOs, hospitality and workplaces are treated differently, so confirm with building control or a fire safety adviser for your project.

Where should I look for recommended light levels?

Start with the SLL Code for Lighting, published by CIBSE, which sets out the fundamentals and recommendations for applying light in buildings. For complex or regulated spaces, ask a lighting designer to confirm the calculations against the relevant British and European standards.

When should lighting controls be decided?

At layout stage, before the ceiling and electrical first fix are fixed. The dimming protocol must match the drivers in the fittings, and sensors and keypads need positions on the drawings. Changing controls later usually means changing drivers, cabling or both.

Can I see lighting in person before I specify it?

Yes, if you are a trade professional. Faura’s showroom in Westminster is open by appointment to approved trade visitors, with decorative and architectural lighting shown in finished interiors. You can book through the lighting showroom page.

Sources

• Lighting in buildings: top tips, CIBSE
• SLL Code for Lighting, CIBSE
• SLL Code for Lighting (2022), CIBSE
• Emergency lighting, Designing Buildings
• Procurement of facility management, RICS
• Approved Document L, Volume 1: Dwellings, GOV.UK
• Approved Document L, Volume 2: Buildings other than dwellings, GOV.UK

Recommended

• FF&E Spec Writing: A Practical Guide for Interior Designers
• Finishes and Coatings Guide for Interior Designers
• Interior Design Brief: Template and Step-by-Step Guide
• Contract vs Retail Furniture: A Specification Guide for Designers