Lumen to Lux to Candela Converter

Convert Between Light Units

Calculate and convert between luminous flux (lumen), illuminance (lux), and luminous intensity (candela). Essential for lighting design and photometry calculations.

Practical Examples

Common lighting scenarios and their unit conversions

Office Lighting

Lumen to Lux

Converting 3000 lumen LED panel to lux on 10m² desk area

Conversion: lumen-to-lux

Lumen: 3000 lm

Area: 10 m²

Spotlight Calculation

Candela to Lumen

Converting 1500 candela spotlight with 30° beam angle to lumens

Conversion: candela-to-lumen

Candela: 1500 cd

Beam Angle: 30 °

Room Illumination

Lux to Lumen

Required lumens for 500 lux illumination over 25m² room

Conversion: lux-to-lumen

Lux: 500 lx

Area: 25 m²

Point Light Source

Point Light Source

Calculating illuminance from 2000 candela source at 3m distance

Conversion: candela-to-lux

Candela: 2000 cd

Distance: 3 m

Other Titles
Understanding Light Units: A Comprehensive Guide
Master the relationships between lumen, lux, and candela in lighting and photometry

What are Light Units and Why They Matter

  • Fundamental Light Measurements
  • Importance in Lighting Design
  • International Standards
Light measurement is essential for proper lighting design, energy efficiency, and human comfort. Three fundamental units form the basis of photometry: lumen (luminous flux), lux (illuminance), and candela (luminous intensity).
The Three Pillars of Photometry
Lumen measures the total amount of visible light emitted by a source, regardless of direction. Lux measures how much light actually reaches a surface per unit area. Candela measures the intensity of light in a specific direction.
Why Accurate Conversion Matters
Understanding these relationships is crucial for lighting engineers, architects, and designers to create optimal lighting environments while meeting energy codes and human visual requirements.

Real-World Reference Points

  • A 100W incandescent bulb produces about 1600 lumens
  • Office lighting typically requires 300-500 lux
  • A candle produces approximately 1 candela

Step-by-Step Guide to Light Unit Conversions

  • Lumen to Lux Conversion
  • Candela to Lumen Conversion
  • Point Source Calculations
Converting between light units requires understanding the geometric relationships and the specific application context. Each conversion serves different lighting design purposes.
Lumen to Lux: Area-Based Calculation
To convert lumens to lux, divide the luminous flux by the illuminated area: Lux = Lumens ÷ Area (m²). This assumes uniform distribution over the surface.
Candela to Lumen: Solid Angle Method
Convert candela to lumens using the solid angle: Lumens = Candela × Solid Angle (steradians). For a cone: Ω = 2π(1 - cos(θ/2)) where θ is the full beam angle.
Point Source Illuminance
For a point light source, illuminance follows the inverse square law: Lux = Candela ÷ Distance² (m²). This is fundamental for calculating lighting at specific distances.

Step-by-Step Conversion Examples

  • 3000 lm ÷ 15 m² = 200 lux average illumination
  • 1000 cd × 0.84 sr = 840 lm for 60° beam
  • 500 cd ÷ (2m)² = 125 lux at 2 meters

Real-World Applications of Light Unit Conversions

  • Architectural Lighting Design
  • Industrial and Commercial Applications
  • Photography and Film Lighting
Light unit conversions are essential across numerous professional fields, from architectural design to industrial safety, each requiring specific illumination levels and distribution patterns.
Architectural and Interior Design
Architects use these conversions to specify appropriate luminaires for different spaces. Residential areas typically need 100-300 lux, while precision work areas require 500-1000 lux or more.
Industrial Safety and Compliance
Industrial facilities must meet specific illuminance requirements for worker safety. Manufacturing areas typically require 200-500 lux, while inspection areas need 1000+ lux.
Photography and Cinematography
Professional lighting technicians use these conversions to achieve desired exposure levels and lighting ratios, ensuring optimal image quality and mood.

Industry-Specific Requirements

  • Hospital operating rooms: 10,000-100,000 lux
  • Street lighting: 5-20 lux average
  • Studio photography: 1,000-10,000 lux typical

Common Misconceptions and Correct Methods

  • Uniform vs. Non-uniform Distribution
  • Color Temperature Considerations
  • Measurement Distance Effects
Many lighting calculations contain common errors that lead to incorrect results. Understanding these pitfalls helps ensure accurate lighting design and energy efficiency.
The Uniform Distribution Assumption
The simple lumen-to-lux formula assumes uniform light distribution, which rarely occurs in real applications. Actual illuminance varies significantly across the illuminated surface.
Ignoring Light Source Characteristics
Different light sources have varying beam patterns and efficiency. A spotlight with narrow beam angle will have higher peak candela but may produce fewer total lumens than expected.
Distance and Angle Effects
The inverse square law applies only to point sources. For extended sources or when the measurement distance is comparable to source size, more complex calculations are needed.

Common Calculation Errors

  • LED panel edge vs. center can vary by 50%
  • Cosine law affects angled illumination
  • Room reflectance significantly impacts actual lux levels

Mathematical Derivation and Advanced Examples

  • Photometric Relationships
  • Solid Angle Calculations
  • Complex Lighting Scenarios
The mathematical relationships between light units derive from fundamental photometric principles and geometric optics, providing the foundation for all lighting calculations.
Fundamental Photometric Equation
The relationship E = I/r² cos(θ) describes illuminance (E) from a point source with intensity (I) at distance (r) and angle (θ). This forms the basis for all photometric calculations.
Solid Angle Mathematics
For circular cones, the solid angle Ω = 2π(1 - cos(α)) where α is the half-angle. This relationship is crucial for converting between luminous intensity and luminous flux.
Complex Multi-Source Scenarios
Real lighting designs involve multiple sources with different characteristics. Superposition principles apply: total illuminance equals the sum of individual contributions from each source.

Advanced Mathematical Applications

  • Ω = 2π(1 - cos(30°)) = 0.84 steradians for 60° cone
  • Four 1000 lm sources can provide 4000 lm total flux
  • Angled surface: E = E₀ × cos(incident angle)