LED Lumen, Candela & Lux Calculator
This LED photometric calculator converts between lumens, candela, and lux, and estimates luminous efficacy, fixture lumens, and LED quantity for lighting design.
Use it for first-order beam, illuminance, and output estimates before validating real LED optics with datasheets and measurements.
Engineering tool
LED Lumen, Candela & Lux Calculator
Convert lumens, candela, lux, beam angle, distance, efficacy, and LED quantity for photometric LED estimates.
Total visible light output.
Full beam angle used for the cone solid angle.
Candela
1,187.948668 cd
Result console
- Candela
- 1,187.948668cd
- Beam solid angle
- 0.841787sr
- Lumens
- 1,000lm
Engineering Notes
- Beam efficiency depends on the real optical distribution; this assumes a symmetric cone.
Photometric estimate is within typical engineering input ranges.
Formula reference
LED Photometric Formulas
Photometric calculations depend on optical assumptions. The solid-angle equation assumes a symmetric cone beam.
Ω = 2π(1 - cos(θ / 2))Candela = Lumens / ΩLumens = Candela × ΩLux = Candela / Distance²Lumens = Lux × Area / (UF × MF)lm/W = Lumens / WattsLED Count = ceil(Target Lumens × (1 + Margin) / Lumens per LED)Variable definitions
- lm
- Lumens, total luminous flux
- cd
- Candela, luminous intensity
- lx
- Lux, illuminance on a surface
- Ω
- Solid angle in steradians
- θ
- Full beam angle
- UF
- Utilization factor
- MF
- Maintenance factor
Variable Definitions
- Luminous flux
- Lumens describe the total visible light emitted by a source.
- Luminous intensity
- Candela describes light intensity in a specific direction.
- Illuminance
- Lux describes how much light reaches a surface area.
- Beam angle
- The angular spread used to estimate beam solid angle.
- Solid angle
- The three-dimensional beam angle measured in steradians.
- Luminous efficacy
- Lumens per watt; this is different from electrical efficiency.
How to Use
1. Pick a photometric relation
Choose conversion, lux estimate, efficacy, or LED quantity mode.
2. Enter optical assumptions
Use beam angle, distance, area, utilization factor, and maintenance factor where relevant.
3. Validate with measurements
Real optics, lenses, reflectors, and installation geometry can change the result.
Worked Examples
Lumens to Candela
1000 lm and 60° beam angle show the beam solid angle and candela.
Candela to Lux
500 cd at 2 m gives 125 lx.
Lux to Lumens
500 lx over 20 m² gives 10000 lm with UF = 1 and MF = 1.
Luminous Efficacy
1500 lm from 12 W gives 125 lm/W, classified as Efficient.
LED Quantity
6000 lm target, 150 lm per LED, and 20% margin requires 48 LEDs.
Lumens vs lux
Lumens alone cannot determine illuminance because distance, beam angle, and area matter.
Inverse square law
For an ideal point source, illuminance decreases with the square of distance.
Beam angle matters
A narrow beam concentrates lumens into higher candela and higher center lux.
Solid angle is approximate
Real LED optics may not produce a uniform cone of light.
Utilization and maintenance
Fixture losses, dirt, aging, and geometry reduce delivered lumens.
Efficacy is not efficiency
Luminous efficacy reports lm/W and is not the same as electrical conversion efficiency.
Common Mistakes
- Confusing lux with lumens.
- Ignoring beam angle.
- Ignoring distance.
- Treating candela as overall brightness.
- Assuming luminous efficacy equals electrical efficiency.
- Ignoring utilization factor.
- Ignoring maintenance factor.
Support reference
FAQ
What is the difference between lumens, candela and lux?
Lumens measure total luminous flux, candela measures luminous intensity in a direction, and lux measures illuminance on a surface.
How do you convert lumens to candela?
Calculate the beam solid angle from beam angle, then divide lumens by the solid angle: cd = lm / sr.
How do you calculate lux from candela?
For an ideal point source, lux is candela divided by distance squared: lx = cd / m².
Why does beam angle affect candela?
The same lumen output concentrated into a narrower beam has a smaller solid angle and therefore higher candela.
Is luminous efficacy the same as electrical efficiency?
No. Luminous efficacy is lumens per watt, while electrical efficiency compares electrical input and useful output energy.
Can lumens alone determine illuminance?
No. Illuminance also depends on beam angle, distance, optics, surface area, utilization, and maintenance factors.
Documentation
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Engineering Disclaimer
This calculator provides first-order photometric estimates. Real LED performance depends on optics, thermal conditions, binning, measurement geometry, driver current, aging, and installation environment.