Every architect has walked into a finished space and felt that something was off. The
proportions were right, the materials were right — but the light was flat, or harsh, or the
wrong shade of white, and it flattened everything. Nine times out of ten, the design was fine.
The lighting specification was the weak link.
Lighting is often the last thing specified and the first thing value-engineered. If your spec
is vague, someone downstream will fill the gap with the cheapest fitting that technically
complies. Here are the four numbers that protect your vision — and how to lock them down.
1. CRI — The Number That Decides How Materials Look
Colour Rendering Index (CRI) measures how truthfully a light reveals colour, on a scale to
100. It is the single most important — and most ignored — spec for design quality. Under low-CRI
light, your carefully chosen timber looks grey, fabrics look muddy, and skin tones look ill.
- CRI 80+ — the minimum for any occupied space
- CRI 90+ — for retail, hospitality, galleries, residences, anywhere
materials and skin tones matter
Write a minimum CRI into the spec. It is the easiest thing for a contractor to shave, and the
most visible when they do.
2. Colour Temperature (CCT) — The Mood Dial
CCT, in Kelvin, sets whether a space feels warm and intimate or crisp and clinical. The
mistake is not choosing wrong — it is being inconsistent, so one area glows warm and the next
reads cold blue.
| CCT | Feel | Best For |
|---|---|---|
| 2700–3000K | Warm, intimate | Homes, hotels, restaurants |
| 3500–4000K | Neutral, natural | Offices, retail, lobbies |
| 5000–5700K | Cool, energetic | Workshops, clinical, task areas |
Specify one CCT per space type and hold the whole project to it.
3. Glare — The Silent Ruiner of Good Design
A beautiful room with glaring fixtures is an uncomfortable room. Glare is controlled through
optics, shielding, and how deep the light source sits in the fitting. For screen-based
workspaces, ask for a controlled glare rating (UGR 19 or below is a common target). Deep-set,
well-shielded fixtures almost always look more considered than cheap flush panels.
4. Light Levels & Lighting Power Density
Specify the lux each space needs — and, increasingly, the Lighting
Power Density (LPD), the watts per square metre. LPD keeps you honest on energy and is
often required for green ratings like
IGBC. High-efficacy LED lets you hit the light level you want within a tight power budget.
The Spec Sheet That Cannot Be Watered Down
For each fixture type, state: minimum CRI, exact CCT, minimum efficacy (lm/W), glare rating,
IP rating where relevant, and required certifications (BIS, LM-79, LM-80). Add the phrase “or approved equivalent
meeting all listed parameters” — so any substitution must match your numbers, not just the price.
Frequently Asked Questions
What CRI should an architect specify?
CRI 80+ as a minimum for occupied spaces, and 90+ for retail, hospitality, galleries and
residences where colour accuracy matters.
What is LPD in lighting?
Lighting Power Density — the lighting wattage per square metre. Lower LPD means a more
energy-efficient design, and it is often required for green certification.
How do I stop contractors substituting cheaper fittings?
Specify minimum values for CRI, CCT, efficacy, glare and certifications, and require any
equivalent to meet every listed parameter — not just match the price.
Which colour temperature is best?
It depends on mood: 2700–3000K for warm spaces, 4000K for neutral working areas, 5000K+ for
task and clinical settings. Consistency across the project matters most.
Reway supplies high-CRI, glare-controlled
architectural and commercial LED lighting with full LM-79 and LM-80 documentation — so your
spec is met, not compromised. Discuss your
project with our team →
