lux (lx)
1 lux = 1 lumen per square metre
What is lux?
Lux is the SI unit of illuminance, measuring luminous flux received per unit area. It is the standard unit for evaluating lighting conditions in workplaces, photography studios, building codes, and health and safety standards.
Notes: Base unit for illuminance
Real-world uses
Lux is the SI unit of illuminance used in architectural lighting design, workplace safety regulations, and photography. Office lighting standards typically require 300–500 lux, hospital operating rooms need about 10,000 lux, and direct sunlight provides roughly 100,000 lux.
History
The lux was adopted as the SI unit of illuminance, derived from the Latin word "lux" meaning light. It replaced older units like the foot-candle and phot. One lux equals one lumen per square metre, standardized with the SI system in 1960.
Common mistakes
Confusing lux (illuminance on a surface) with lumens (total light output from a source). A 800-lumen bulb produces different lux readings depending on the distance and angle. Also, lux does not account for light colour or quality.
When is this conversion used?
Converting lux to lumen per square metre is useful in the illuminance domain when comparing values across different measurement standards or applying formulas that require a specific unit.
How to convert lux to lumen per square metre
To convert lux to lumen per square metre, multiply the value by 1.
Conversion formula (from base unit)
x * 1.0
Measurement standards
The lux is the SI derived unit of illuminance, defined as one lumen per square metre (lm/m²). The CIE (International Commission on Illumination) provides standard illuminance recommendations for various visual tasks, which most national standards bodies adopt directly.
Did you know?
Direct sunlight at noon on a clear day delivers roughly 100,000 lux, while a dimly lit room might have only 50 lux. The human eye can function across a range of over 10 billion to one from starlight to direct sun — one of the widest dynamic ranges of any biological sensor.
| lux | lumens per square metre |
|---|---|
| 0.1 | 0.1 |
| 0.5 | 0.5 |
| 1 | 1 |
| 2 | 2 |
| 5 | 5 |
| 10 | 10 |
| 25 | 25 |
| 50 | 50 |
| 100 | 100 |
| 250 | 250 |
| 500 | 500 |
| 1,000 | 1,000 |
Common values
| lux | lumens per square metre | |
|---|---|---|
| Full moon, clear night | 0.1 lux | 0.1 lumens per square metre |
| Living room lighting | 100 lux | 100 lumens per square metre |
| Office lighting | 500 lux | 500 lumens per square metre |
| Overcast daylight | 1,000 lux | 1,000 lumens per square metre |
| Direct sunlight | 100,000 lux | 100,000 lumens per square metre |
Full lux conversion table
| Unit | Value | Factor |
|---|---|---|
| lumen per square metre | 1 lx = 1 lm/m² | × 1 |
| foot-candle | 1 lx = 0.09290304 fc | × 0.09290304 |
| phot | 1 lx = 0.0001 ph | × 0.0001 |