Convert Lumens to Lux – Light Converter
This converter translates luminous flux (lumens, the total light output of a source) into illuminance (lux, lumens per square meter) under clearly stated assumptions. Use it for rough planning, specification checks, and comparing product ratings.
Because lumens measure total emitted light while lux measures light incident on a surface, the conversion requires an assumption about how that flux is distributed in space (uniform over an area, point-source inverse-square distribution, or directed beam). Measured lux can differ from calculated lux when fixtures are directional, surfaces are reflective, or distances are small.
Governance
Record 3a34c148872c • Reviewed by Fidamen Standards Committee
Interactive Converter
Convert between lumen and lux with precision rounding.
Quick reference table
| Lumen | Lux |
|---|---|
| 1 lm | LUX 1.00 lx |
| 5 lm | LUX 5.00 lx |
| 10 lm | LUX 10.00 lx |
| 25 lm | LUX 25.00 lx |
| 50 lm | LUX 50.00 lx |
| 100 lm | LUX 100.00 lx |
Methodology
Primary conversion uses the definition of illuminance: E (lux) = Φ (lumens) / A (m²) when the luminous flux is spread uniformly over a surface area A. This is exact when surface receives flux evenly and there are no losses.
For a point-like isotropic source (uniform emission in all directions) at distance r (meters), use the inverse-square relation: E = Φ / (4π r²). This assumes the source approximates a point and that the surface is perpendicular to the incoming light.
For directional fixtures with a known beam solid angle or luminous intensity profile, convert lumens to candela or use the beam angle to compute the illuminated area at the target distance, then apply E = Φ_on_target / A_target. For non-uniform patterns, photometric files (IES/LM50) or lux meters are required for accurate results.
Key takeaways
Use E = Φ/A for uniform distributions and E = Φ/(4πr²) for isotropic point approximations. For directional fixtures, convert lumens to intensity and account for beam angle or use photometric files.
Calculated lux is an estimate unless you have accurate photometric data or a calibrated lux meter. Follow recognized measurement and calibration standards when precision is required.
Worked examples
Example 1 — Uniform area: A lamp rated 1200 lm uniformly lights a 4 m² table. E = 1200 lm ÷ 4 m² = 300 lx.
Example 2 — Point-source at distance: A point-like 600 lm bulb 2 m from a surface gives E = 600 ÷ (4π × 2²) ≈ 600 ÷ (50.265) ≈ 11.93 lx.
F.A.Q.
What is the difference between lumens and lux?
Lumens (lm) measure total light emitted by a source. Lux (lx) measures light arriving at a surface: 1 lx = 1 lm/m². Lux depends on how the emitted lumens are distributed over area and distance.
Can I always convert lumens to lux exactly?
No. Exact conversion requires knowledge of the spatial distribution of the flux. Without uniform distribution or precise photometric data, conversions are estimates. Use photometric files (IES/LM50) or a calibrated lux meter for accurate measurements.
How does distance affect lux?
For a point-like or small source, illuminance falls approximately with the square of distance (inverse-square law). For extended or directional sources, the relationship differs and depends on beam shape and angle.
When should I use a lux meter?
Use a calibrated lux meter when you need measured illuminance for compliance, safety checks, workplace lighting (OSHA/industry requirements), or precise verification of installation performance.
What are common sources of error in calculated lux?
Common errors include assuming uniform distribution, neglecting fixture beam patterns, ignoring surface orientation and reflectance, using wrong distance, and mixing units (ft² vs m²).
How to convert square feet to square meters?
Multiply square feet by 0.092903 to get square meters. Always convert area to m² before using E = Φ/A.
What should I know about calibration and standards?
For traceable measurements use equipment calibrated to national/international standards. Refer to NIST, ISO, and CIE guidance on photometric measurements and calibration procedures.
Sources & citations
- NIST — Photometry and Radiometry resources — https://www.nist.gov/pml/weights-and-measures/photometry-and-radiometry
- CIE — International Commission on Illumination — https://cie.co.at
- ISO — International Organization for Standardization (lighting standards) — https://www.iso.org/committee/52562.html
- IEEE Standards Association — Lighting and photometric measurement guidance — https://standards.ieee.org
- OSHA — Workplace lighting recommendations and regulations — https://www.osha.gov/SLTC/lighting
- ISO 80000-7:2019 — Light and radiation — https://www.iso.org/standard/64978.html
- NIST SP 811 — Guide for the Use of the International System of Units — https://www.nist.gov/pml/special-publication-811
Further resources
Related tools
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
Record ID: 3a34c148872cWhat changed (latest)
v1.0.0 • 2025-11-30 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
What changed (latest)
v1.0.0 • 2025-11-30 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Engine
v1.0.0
Data
Baseline (no external datasets)
Content
v1.0.0
UI
v1.0.0
Governance
Last updated: Nov 30, 2025
Reviewed by: Fidamen Standards Committee (Review board)
Credentials: Internal QA
Risk level: low
Reviewer profile (entity)
Fidamen Standards Committee
Review board
Internal QA
Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person
Semantic versioning
- MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
- MINOR: New features or fields that do not change existing outputs for the same inputs.
- PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.
Review protocol
- Verify formulas and unit definitions against primary standards or datasets.
- Run golden-case regression suite and edge-case suite.
- Record reviewer sign-off with credentials and scope.
- Document assumptions, limitations, and jurisdiction applicability.
Assumptions & limitations
- Uses exact unit definitions from the Fidamen conversion library.
- Internal calculations use double precision; display rounding follows the unit's configured decimal places.
- Not a substitute for calibrated instruments in regulated contexts.
- Jurisdiction-specific rules may require official guidance.
Change log
v1.0.0 • 2025-11-30 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 97a22ed86949