Convert Lux to Lumens – Light Calculator
This tool converts illuminance (measured in lux, lx) to total luminous flux (lumens, lm) for a specified area. Use it when you know the illuminance level across a surface and need the total emitted or required luminous flux for that surface.
Enter the illuminance in lux and the surface area in square metres. The calculation assumes uniform illuminance across the surface; if illuminance varies, use area-weighted averages or break the surface into zones and sum the results.
Inputs
Results
Total luminous flux
300
Lumens per square metre (sanity check)
300
| Output | Value | Unit |
|---|---|---|
| Total luminous flux | 300 | lm |
| Lumens per square metre (sanity check) | 300 | lm/m2 |
Visualization
Methodology
The underlying relationship is lumens = lux × area (in square metres). Lux is lumens per square metre, so multiplying by area yields total lumens incident on or required for that area.
Measurement and reporting guidance: use a calibrated illuminance meter whose spectral response approximates the photopic luminous efficiency function. For professional or regulatory work, ensure instruments are calibrated to a laboratory traceable to NIST or an ISO/IEC 17025-accredited calibration provider.
Worked examples
Example 1: 500 lux over 20 m² → lumens = 500 × 20 = 10,000 lm.
Example 2: 300 lux over 1.5 m² → lumens = 300 × 1.5 = 450 lm.
Key takeaways
This calculator gives a direct conversion from lux to lumens when a surface area is provided and assumes uniform illuminance.
For non-uniform lighting, divide the area into zones, compute lumens per zone, and sum. Verify instruments are calibrated and appropriate for the light spectrum encountered.
Further resources
Expert Q&A
Do I need to provide area in square metres?
Yes. Lux is lumens per square metre, so converting to lumens requires the area in square metres. If you have area in other units, convert to m² before using this tool (1 ft² = 0.092903 m²).
Can I convert a lux reading from a handheld meter directly to lumens for a lamp?
Only approximately. A lux reading at a particular point or plane depends on distance, angle, and beam distribution. For a lamp's total lumen output, integrating sphere measurements or manufacturer-rated lumen output are appropriate. Use this tool for area-based estimations of incident luminous flux.
How accurate is the calculated value?
The numerical conversion is exact given the inputs, but real-world accuracy depends on sensor calibration, meter spectral response, angular response, spatial uniformity of illuminance, and rounding. For traceable accuracy use instruments calibrated to NIST or an ISO/IEC 17025-accredited lab and follow measurement standards.
Which standards apply to these measurements?
Relevant references include instrument calibration and measurement practice standards from NIST and ISO, workplace lighting guidance from OSHA and ISO, and consensus technical standards hosted by standards organizations. See citations for authoritative sources.
Sources & citations
- National Institute of Standards and Technology (NIST) — https://www.nist.gov
- ISO 8995-1 / EN 12464-1 (lighting of work places) - ISO catalogue — https://www.iso.org/standard/16861.html
- OSHA: Lighting - Occupational Safety and Health Administration — https://www.osha.gov/lighting
- IEEE Standards and technical resources — https://standards.ieee.org