Lumen to Lux Calculator
Convert lumens (lm) to lux (lx): lx = lm ÷ A. Use area in m² or ft², or isotropic sphere radius. Reverse lux to lumens. Runs locally in your browser.
Trust summary Engine tested · Specification checked · v1.1.0
- Input interpretation
- Enter values to calculate.
- Result
- —
- Model
- Illuminance from luminous flux and area (or sphere radius), or flux from illuminance and area.
- Scope
- Uniform illuminance over the stated area or sphere
- Verification
- Engine tested · Specification checked · v1.1.0
- Named expert review
- Optional · Not performed
- Specification basis
- 1 lx = 1 lm/m²; 1 m² = 10.76391 ft²; sphere A = 4πr²
Formulas
Core equations used by this calculator.
How to use
Choose mode
Area in m² or ft², sphere radius, or the reverse lux → lumens path.
Enter lumens (or lux) and area / radius
Use the lit surface size, or sphere radius for an isotropic full-sphere model.
Read lux or lumens
Same total lumens over a smaller area → higher lux.
Example calculations
Common configurations with formula and result.
1000 lm · 10 m²
Default (area)
1000 lm · 100 ft²
Feet area
1000 lm · r = 1 m
Full sphere
Narrow vs wide
Same 2000 lm
lx → lm
500 lx · 10 m²
Typical illuminance targets (guide)
Common values at a glance.
| Activity | Approx. lux | Notes |
|---|---|---|
| Public / dark outdoor | 20–50 | Orientation |
| Corridors / storage | ~100 | Circulation |
| Classroom | ~300 | EN workplace guide |
| Office / PC work | ~500 | Common desk target |
| Detailed / drawing work | 1000–2000 | Higher visual demand |
| Outdoor construction (varies) | 20–200 | Task-dependent |
Lumen to Lux calculator specification
Version 1.1.0 · Engine tested
- Engine tested 4 published cases
- Named expert review Not performed
- Calculation version 1.1.0
- Definition
- Lux (lx) is illuminance — lumens per square meter on a surface. Lumens (lm) are total luminous flux from the source. With uniform coverage over area A: lx = lm ÷ A(m²). With A in ft²: lx = 10.76391 × lm ÷ A(ft²). For an isotropic source on a sphere of radius r: A = 4πr², so lx = lm ÷ (4πr²).
- What it calculates
- Illuminance from luminous flux and area (or sphere radius), or flux from illuminance and area.
- Inputs
- Lumens (lm) or lux (lx)
- Area (m² or ft²) or sphere radius (m)
- Outputs
- Lux (lm → lx) or lumens (lx → lm)
- Formula
E=Φ/A; E=Φ/(4πr²)- Assumptions
- Uniform illuminance over the stated area or sphere
- All flux reaches that surface
- Units
- lm, m² → lx
- lm, ft² → lx
- lm, r(m) → lx
- Boundary conditions
- A = 0 or r = 0 → undefined (UI returns 0)
- Example
- 1000 lm, 10 m² → 100 lx
- Validation cases
4 published on this page
- 1000 lm, 10 m² → 100 lx
- 1000 lm, 100 ft² → 107.6391 lx
- 1000 lm, r = 1 m → ≈ 79.5775 lx
- 500 lx, 10 m² → lm → 5000 lm
- Specification basis
- 1 lx = 1 lm/m²; 1 m² = 10.76391 ft²; sphere A = 4πr²
- Calculation version
- 1.1.0
Background
Interpretation and common distinctions.
Convert lumens (lm) to lux (lx) by dividing by the illuminated area.
E((lx)) = (Phi((lm)))/(A((m^(2)))) E((lx)) = 10.76391 × (Phi((lm)))/(A((ft^(2))))
Default: 1000 lm · 10 m² → 100 lx.
Lumens vs lux
| Unit | Measures |
|---|---|
| Lumen (lm) | Total light emitted by the source |
| Lux (lx) | Light received per m² on a surface |
- Distance matters: farther away → larger lit area → lower lux for the same lumens.
- Beam shape matters: a narrow spot packs the same lumens into a small A (high lux); a wide flood spreads them (low lux).
Sphere (isotropic) model
When all flux is spread uniformly over a sphere of radius r:
A = 4π r² E((lx)) = (Phi)/(4π r²)
Use the sphere tabs for this path (radius in meters).
Related tools
Other calculators in this family: Lux to Lumen, Lumen to Candela, Candela to Lux, Foot-Candles to Lux .
Frequently asked questions
Key distinctions behind the calculation.
How do I convert lumens to lux?
Divide by the illuminated area in square meters: lx = lm ÷ A. With area in ft², use lx = 10.76391 × lm ÷ A(ft²).
What is the difference between lumens and lux?
Lumens are total light output from the source. Lux is how much of that light lands per square meter on a surface. Same lamp can give different lux depending on distance and beam spread.
Why does distance matter?
Farther away, the same beam covers a larger area, so lux drops. For a point source, illuminance also follows ≈1/d² along the beam axis (see candela to lux).
Same lumens, different brightness — why?
A narrow flashlight concentrates lumens into a small spot (high lux). A wide flood spreads them over a large area (low lux).
When do I use the sphere mode?
When modeling an isotropic source and the lit “surface” is a sphere of radius r: lx = lm ÷ (4πr²). For flat surfaces, enter the actual area instead.
Does this include optical losses?
No. The calculator assumes all stated lumens reach the area uniformly. Real optics spill light and beams are uneven.
How do I get lumens from a lux target?
Use lx → lm: lm = lx × A for the area you need to light.
Is 1 lux equal to 1 lumen?
Only over exactly 1 m². Over 10 m², 1 lx requires 10 lm.