Stop buying lighting by watts. This guide explains exactly how to evaluate LED light output in lumens, compare efficacy across fixtures, and avoid the most common procurement mistake in the LED era.
For 100+ years, watts were a reliable proxy for brightness: a 60W bulb produced roughly 800 lumens, a 100W bulb roughly 1,600 lumens. LED technology broke this relationship completely. A modern LED produces 3-10× more light per watt than incandescent — a 10W LED matches a 60W incandescent, and a 100W LED fixture outshines a 400W metal halide. Wattage now tells you energy consumption, not light output. Lumens tell you brightness.
The procurement rule: always compare lumens first, then check watts (for energy cost). A 4,000 lm fixture at 30W (133 lm/W) is more efficient than a 4,000 lm fixture at 40W (100 lm/W), but both deliver the same light output. When comparing LED to legacy technology: 400W metal halide ≈ 20,000 lm (50 lm/W) vs LED equivalent: 20,000 lm at 133W (150 lm/W) — same light, 67% less energy.
The legacy wattage equivalents (60W replacement, 100W replacement) are marketing shortcuts that cause confusion in procurement. A "100W replacement" LED could be anywhere from 1,200 to 1,800 lumens depending on the manufacturer's interpretation. Always check the actual lumen output — it's the only number that matters for brightness.
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 |
|---|---|---|---|---|---|
| Procurement Scenario | Metric to Compare First | Then Check | |||
| Replacing Existing Fixtures | Match or exceed existing lumens | Lower watts = energy savings | |||
| New Construction (Known Lux Target) | Calculate required lumens | Select efficacy for lifecycle ROI | |||
| Comparing LED to LED | Same lumens → compare watts (efficacy) | CRI, CCT, warranty, IP | |||
| Budget-Limited Project | Minimum acceptable lumens at lowest cost/lm | Efficacy for operating cost |
Lumens first (brightness), watts second (energy cost). Never buy by wattage — always compare lumens, then check efficacy (lm/W) among lumen-equivalent options. The fixture with the right lumens at the highest lm/W wins on lifetime cost.