What is CRI (Colour Rendering Index)?

How CRI Works

CRI is scored on a scale from 0 to 100, where 100 represents perfect colour rendering (identical to a reference source — daylight or incandescent depending on colour temperature). The score is technically referred to as Ra and is calculated by averaging the rendering accuracy across 8 standard test colour samples (R1–R8).

An extended metric, R9, specifically measures deep red rendering — critical in healthcare (skin tone assessment) and retail (food displays). A luminaire might score CRI 80 (Ra80) but have a poor R9 value, making reds appear dull and washed out.

CRI Standards for UK Projects

BS EN 12464-1 specifies minimum CRI values:

• General offices — Ra ≥ 80 • Healthcare — Ra ≥ 80 (Ra ≥ 90 recommended for clinical areas) • Education — Ra ≥ 80 • Industrial (colour-critical) — Ra ≥ 90 • Retail — Ra ≥ 80 (Ra ≥ 90 for fashion and food) • Art galleries, museums — Ra ≥ 90

For most commercial projects in the UK, CRI 80 (Ra80) is the minimum specification standard. EOS recommends CRI 90 (Ra90) for any space where visual quality and occupant comfort are priorities.

Why CRI Matters

Poor colour rendering makes environments feel flat, institutional and uncomfortable — even if lux levels are correct. High-CRI lighting transforms how a space feels:

• Skin tones appear healthy and natural — critical in healthcare consulting rooms and hospitality settings • Food looks fresh and appetising — essential in supermarkets, restaurants and food service • Fabrics and materials show their true colours — important in retail, showrooms and design studios • Artwork and displays are presented accurately — mandatory for galleries and exhibition spaces

All EOS luminaires are available in CRI 80 as standard, with CRI 90+ options across the interior and architectural ranges.