Lux Explained
Lux measures how much light reaches a surface. The most-specified unit in lighting design, and the most-misunderstood.
What Lux Measures
Lux (lx) is the unit of illuminance, the amount of light falling on a surface per square metre. 1 lux = 1 lumen / m².
Why It Matters
Lux describes what reaches the eye, what the user actually experiences. Lumens describe what leaves the fixture. Two rooms with identical fixtures can have very different lux.
Recommended Lux by Function
| Space | Lux |
|---|---|
| Circulation | 100–150 |
| Living areas | 100–200 ambient, 300–500 task |
| Offices | 500 at desk |
| Retail | 300 ambient, 1000+ accent |
| Hospitality | 50–200 ambient, focal task |
How Lux Is Measured
A lux meter at the working plane (typically 0.75m for desks, 0m for floors). Always measure multiple points and average them, peak lux alone is misleading.
Common Mistakes
- Treating lux as a single number rather than distribution
- Measuring at one bright spot
- Comparing lux from different working planes
- Ignoring uniformity
Professional Recommendation
Specify lux with uniformity together, e.g. 500 lux average with U0 ≥ 0.60. One number alone is not a brief.
Lighting Intelligence by Alya
At Ashwamedha Design Solutions, this is part of our Lighting Intelligence practice, every recommendation is validated through DIALux simulation, lux calculations and visual comfort analysis before it reaches a construction site. Alya, our lighting intelligence platform, packages this thinking into reusable design tools.
Frequently Asked Questions
How is lux different from lumens?+
Lumens measure light leaving the fixture. Lux measures light reaching the surface. Lux depends on lumens, distance, beam and reflectance.
What lux is too dark?+
Below the recommended level for the task. A bedroom at 100 lux ambient is comfortable; an office at 100 lux is unworkable.
Related Service
Lighting Intelligence & DIALux
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