Lumen Calculator
Convert between lumens, lux, and candela for lighting calculations
How to Use This Calculator
Select Calculation Type
Choose whether you want to convert from lumens to lux (illuminance) or from lumens to candela (luminous intensity).
Enter Luminous Flux
Input the total luminous flux in lumens. This is the total amount of visible light emitted by the source. Common values: 800 lm (LED bulb), 1600 lm (bright LED).
Enter Distance (for Lux)
If calculating lux, enter the distance from the light source in meters. Lux measures illuminance (light per unit area) and depends on distance.
Calculate
Click the "Calculate" button to get the illuminance in lux or luminous intensity in candela.
Formulas
Lumen to Lux
Lux = Lumen / Area = Lumen / (4πd²)
Where:
- Lux = Illuminance (lm/m²)
- Lumen = Luminous flux (lm)
- d = Distance from source (m)
Lumen to Candela
Candela = Lumen / (4π)
Where:
- Candela = Luminous intensity (cd)
- Lumen = Luminous flux (lm)
- 4π = Full solid angle (steradians)
Note: This assumes an isotropic (uniform) light source.
Example Calculation (Lumen to Lux):
For an 800 lumen source at 1 meter:
Lumen = 800 lm
d = 1 m
Area = 4π × 1² = 12.57 m²
Lux = 800 / 12.57 = 63.7 lux
About Lumen Calculator
This calculator helps you convert between different units of light measurement: lumens (luminous flux), lux (illuminance), and candela (luminous intensity). Lumens measure total light output, lux measures light per unit area (illuminance), and candela measures light intensity in a specific direction. Understanding these relationships is essential for lighting design, photography, and understanding light specifications.
When to Use This Calculator
- Lighting Design: Calculate illuminance levels for indoor and outdoor lighting
- Photography: Understand light levels and exposure requirements
- Architecture: Design lighting systems with appropriate illuminance
- Education: Learn about photometric units and their relationships
- Product Selection: Compare light sources and understand specifications
Why Use Our Calculator?
- ✅ Multiple Conversions: Convert between lumens, lux, and candela
- ✅ Instant Results: Get accurate conversions immediately
- ✅ Easy to Use: Simple interface with clear input fields
- ✅ Educational: Includes formula explanations and examples
- ✅ 100% Free: No registration required
Common Applications
Interior Lighting: Lighting designers use these calculations to ensure adequate illuminance levels. For example, reading requires about 300-500 lux, while general office lighting needs 300-500 lux.
Photography: Photographers use lux measurements to understand available light levels and determine appropriate camera settings. Different lighting conditions require different ISO, aperture, and shutter speed combinations.
Outdoor Lighting: Street lighting and security lighting require specific lux levels. Understanding the relationship between lumens and lux helps design appropriate lighting systems.
Tips for Best Results
- Remember that lux decreases with the square of distance from the source
- Real light sources are not perfectly isotropic; actual values may differ
- For directional sources (like LEDs), candela values vary with direction
- Lumen ratings on bulbs are total output; actual illuminance depends on distance and direction
- For practical lighting, consider light distribution patterns and reflectors
- Standards recommend different lux levels for different activities (e.g., 500 lux for reading)
Frequently Asked Questions
What's the difference between lumens, lux, and candela?
Lumens measure total light output (luminous flux). Lux measures light per unit area (illuminance, lm/m²). Candela measures light intensity in a specific direction (luminous intensity). Lumens are the total, lux is lumens per area, and candela is lumens per solid angle.
Why does lux decrease with distance?
Lux measures illuminance (light per unit area). As light spreads out from a source, it covers a larger area, so the light per unit area decreases. This follows the inverse square law: illuminance is inversely proportional to the square of distance.
What is a typical lumen value for household lighting?
Typical LED bulbs range from 400-1600 lumens. A 60W incandescent equivalent LED is about 800 lumens. A 100W equivalent is about 1600 lumens. The exact value depends on the bulb type and efficiency.
How many lux is good for reading?
Reading typically requires 300-500 lux for comfortable reading. General office work needs 300-500 lux. Task lighting can provide 500-1000 lux for detailed work. Outdoor daylight provides 10,000-100,000 lux.
Does the calculator account for light directionality?
The calculator uses isotropic (uniform) source assumptions. Real light sources like LEDs have directional emission patterns. For directional sources, actual lux values will be higher in the main direction and lower at angles. The calculator provides an approximation for uniform sources.