The comprehensive color temperature reference: what every Kelvin value means, which CCT to use for every lighting application, how CCT affects mood and perception, and the CCT-CRI-lux interaction matrix.
Correlated Color Temperature (CCT) measured in Kelvin (K) describes the color appearance of white light. Lower Kelvin = warmer (more yellow/amber), higher Kelvin = cooler (more blue). The scale: 2700K — very warm white (incandescent-like), cozy and intimate; 3000K — warm white, most common for residential and hospitality; 3500K — neutral-warm, transitional; 4000K — neutral white, the professional standard for offices, retail, and industrial; 5000K — cool white, high visual acuity, clinical feel; 6500K — daylight, maximum blue content, for color-critical work.
The Kruithof curve captures a real phenomenon: warm CCTs feel pleasant at lower lux levels, cool CCTs feel appropriate at higher lux. 2700K at 500 lx feels oppressively yellow. 6500K at 100 lx feels cold and dim. This CCT-lux interaction is essential for occupant comfort — always specify CCT together with target illuminance.
Choosing the right CCT is about matching the light to the activity and the space. A 3000K cozy living room, a 4000K productive office, and a 5000K inspection station all feel natural because the CCT matches the visual task and occupant expectations.
Getting lux right is not optional — it's a regulatory requirement under EN 12464-1 (Lighting of Indoor Workplaces), which mandates minimum maintained illuminance levels for every office zone. Undershooting causes eye strain, headaches, and productivity loss. Overshooting wastes energy and causes glare. This guide gives you the exact numbers.
The table below lists maintained illuminance (Ēm) requirements for every common office zone per EN 12464-1. Use these values as the minimum design target — going slightly higher (10–20%) is acceptable to account for future degradation.
| Office Zone | Ēm (Maintained Lux) | Uniformity U₀ | UGR Limit | Ra (CRI) Min | Notes |
|---|---|---|---|---|---|
| 💻 Workstation (Desk) | 500 lx | ≥ 0.6 | < 19 | ≥ 80 | Measured on the task area (desk surface). Writing, typing, reading, data processing. |
| 🤝 Meeting / Conference Room | 500 lx | ≥ 0.6 | < 19 | ≥ 80 | Ensure dimmable for presentations. Consider tunable white for video calls. |
| 🎨 Design Studio / CAD Office | 750 lx | ≥ 0.7 | < 16 | ≥ 90 | Higher visual acuity for detailed technical drawings. Stricter UGR. |
| ☕ Break Room / Pantry | 200–300 lx | ≥ 0.4 | < 22 | ≥ 80 | Relaxation zone — lower illuminance acceptable. Warmer CCT (3000K) preferred. |
| 🚶 Corridor / Circulation | 150–200 lx | ≥ 0.4 | < 25 | ≥ 80 | Floor-level measurement. Emergency egress paths require minimum 0.5 lx backup. |
| 🗄️ Filing / Archive Room | 200–300 lx | ≥ 0.4 | < 22 | ≥ 80 | Vertical illuminance on shelves should be ≥ 150 lx at 0.2 m from floor. |
| 🚻 Reception / Lobby | 300–500 lx | ≥ 0.5 | < 22 | ≥ 80 | Higher end (500 lx) for reception desks where reading and visitor interaction occurs. |
| 🖨️ Print / Copy Area | 300–500 lx | ≥ 0.4 | < 19 | ≥ 80 | 300 lx general + 500 lx at service areas for maintenance tasks. |
| 🔧 Server / Technical Room | 200 lx | ≥ 0.4 | < 25 | ≥ 80 | Primarily for maintenance access. Emergency lighting required. |
Lux is a Goldilocks parameter — too little and people suffer; too much and you waste money while creating glare. Here's what happens at each level for a standard office workstation:
Key takeaway: The 450–550 lx range is the sweet spot for standard offices. Below 300 lx is a health and compliance risk. Above 750 lx wastes energy without meaningful visual improvement — the human eye's perceived brightness follows a logarithmic curve, so doubling lux from 500 to 1,000 only feels ~40% brighter.
Standard workstation illuminance. Uniform distribution across all desks critical.
Task + ambient layered. Desk lamp for focused 750 lx on documents, ambient at 300–500 lx.
High visual acuity for detailed drawings. CRI 90+ mandatory. Stricter UGR < 16.
500 lx general + 1,000 lx on examination areas. Tunable white for circadian support.
Use this table to quickly match your office type to the correct lux level and fixture specification. All values comply with EN 12464-1:2021.
| Office Type | Recommended Lux (Ēm) | CCT | CRI (Ra) | UGR | Suggested Fixture |
|---|---|---|---|---|---|
| Application | Recommended CCT | Notes | |||
| Residential Living | 2700-3000K | Warm, relaxing; 2700K for bedrooms/living, 3000K for kitchens | |||
| Office (General) | 4000K | EN 12464-1 standard; promotes alertness | |||
| Retail (Fashion) | 2700-3000K | Flatters skin tones and fabrics | |||
| Retail (Grocery) | 4000K | Fresh food looks natural, not yellow | |||
| Warehouse | 4000K | Standard for picking and packing | |||
| Hospital (Patient) | 3000-4000K | Tunable-white ideal; warmer at night | |||
| Industrial QC | 5000K | Maximum visual acuity for defect detection | |||
| Outdoor / Street | 3000-4000K | 3000K for residential, 4000K for highways |
Match CCT to the activity: 2700-3000K for relaxation and hospitality, 3500-4000K for work and commerce, 5000K+ for precision and inspection. Always pair CCT with the target lux — warm CCT at high lux feels wrong; cool CCT at low lux feels cold. When in doubt, 4000K is the safest default for commercial spaces.