What is Colour Temperature (CCT)?

The Kelvin Scale

Colour temperature is expressed in Kelvin (K). Common values for commercial LED lighting:

• 2700K — Warm white. Soft, relaxed ambience similar to incandescent lamps. Used in hospitality, residential and reception areas. • 3000K — Warm white. Slightly crisper than 2700K. Popular in boutique retail, restaurants and hotel lobbies. • 4000K — Neutral white. The most specified colour temperature for UK commercial interiors — offices, classrooms, healthcare. Balances warmth with visual clarity. • 5000K — Cool white. Higher visual acuity, common in industrial, laboratory and clinical environments. • 6500K — Daylight. Very cool, bluish-white. Used in specialist applications such as colour-critical inspection and some healthcare settings.

The 'best' colour temperature is always project-specific — there is no universal right answer.

Colour Temperature and Wellbeing

Research in circadian lighting shows that colour temperature affects alertness, mood and sleep patterns. Cooler, higher-Kelvin light suppresses melatonin production and promotes alertness during the day, while warmer light in the evening supports relaxation and natural sleep cycles.

This is the foundation of tuneable white lighting — luminaires that can dynamically shift between warm and cool white throughout the day. EOS offers tuneable white (DALI DT8) variants across our interior range, enabling circadian lighting schedules in offices, hospitals and schools.

Specifying Colour Temperature in the UK

BS EN 12464-1 does not mandate a specific colour temperature but recommends that correlated colour temperature (CCT) be appropriate to the task and environment. CIBSE guidance suggests:

• Offices — 3000K–4000K • Healthcare — 4000K general areas, tuneable white in wards • Education — 4000K • Retail — varies by brand identity (2700K–4000K) • Industrial — 4000K–5000K

Consistency is critical — mixing different colour temperatures in the same space creates visual discomfort and appears unprofessional. Always specify a single CCT per zone unless using tuneable white.