lumen per square metre (lm/m²)
1 lumen per square metre = 1 lux
What is lumen per square metre?
Lumen per square metre is a unit of illuminance numerically equivalent to lux. It expresses the amount of light falling on a surface and is used in lighting engineering and photometry to quantify light intensity at a specific location.
Notes: Equivalent to lux
Real-world uses
Lumen per square metre is the explicit form of the lux and is used interchangeably in lighting engineering specifications. It appears in technical datasheets where the relationship between luminous flux (lumens) and illuminated area needs to be made explicit.
History
Lumen per square metre is simply the expanded definition of the lux. The lumen itself was standardized in the early 20th century based on the candela (unit of luminous intensity). The notation lm/m² is used when dimensional clarity is needed in calculations.
Common mistakes
Treating lm/m² as a different unit from lux—they are identical (1 lm/m² = 1 lux exactly). Also, confusing luminous flux per unit area (lm/m², an illuminance) with luminance (cd/m², brightness perceived from a surface).
When is this conversion used?
Converting lumen per square metre to lux is useful in the illuminance domain when comparing values across different measurement standards or applying formulas that require a specific unit.
How to convert lumen per square metre to lux
To convert lumen per square metre to lux, 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.
| lumens per square metre | lux |
|---|---|
| 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
| lumens per square metre | lux | |
|---|---|---|
| Full moon, clear night | 0.1 lumens per square metre | 0.1 lux |
| Living room lighting | 100 lumens per square metre | 100 lux |
| Office lighting | 500 lumens per square metre | 500 lux |
| Overcast daylight | 1,000 lumens per square metre | 1,000 lux |
| Direct sunlight | 100,000 lumens per square metre | 100,000 lux |
Full lumen per square metre conversion table
| Unit | Value | Factor |
|---|---|---|
| lux | 1 lm/m² = 1 lx | × 1 |
| foot-candle | 1 lm/m² = 0.09290304 fc | × 0.09290304 |
| phot | 1 lm/m² = 0.0001 ph | × 0.0001 |