Lux to Candela Calculator
Lux to Candela Calculator – Convert Illuminance to Luminous Intensity
A Lux to Candela Calculator helps you convert illuminance (lux) into luminous intensity (candela) based on the distance from the light source.
This tool is essential for:
- Lighting design
- Beam angle calculations
- Flashlight and LED testing
- Stage and studio lighting
- Architectural illumination planning
Understanding this conversion allows you to determine how powerful a light source is based on measured illumination.
Understanding the Units
What is Lux (lx)?
Lux measures illuminance, which is the amount of light falling on a surface.
1 \text{ lux} = 1 \text{ lumen per square meter}
$$
It tells you how bright a surface appears.
Example:
- Office lighting: 300–500 lux
- Outdoor daylight: 10,000+ lux
- Studio lighting: 1000+ lux
What is Candela (cd)?
Candela measures luminous intensity — the amount of light emitted in a specific direction.
It describes how concentrated or powerful a light beam is.
The Relationship Between Lux and Candela
Lux and candela are related through distance using the inverse square law.
Lux to Candela Formula
\text{Candela (cd)} = \text{Lux (lx)} \times \text{Distance}^2
$$
Where:
- Lux = measured illuminance
- Distance = meters from light source
- Distance² = square of the distance
Why Distance Matters
Light spreads out as it travels.
When distance doubles:
- Lux decreases by 4 times
- Candela remains constant
This is called the Inverse Square Law of Light.
Step-by-Step Examples
Example 1
Measured illuminance = 500 lux
Distance = 2 meters
cd = 500 \times 2^2
$$
cd = 500 \times 4 = 2000 , cd
$$
The light source has 2000 candela intensity.
Example 2
Measured lux = 150 lux
Distance = 3 meters
cd = 150 \times 3^2
$$
cd = 150 \times 9 = 1350 , cd
$$
Example 3
Measured lux = 1000 lux
Distance = 1.5 meters
cd = 1000 \times 1.5^2
$$
cd = 1000 \times 2.25 = 2250 , cd
$$
How the Lux to Candela Calculator Works
- Enter Lux (lx)
- Enter Distance (meters)
- Click Calculate
- Instantly get Candela (cd)
Advanced versions may also:
- Convert meters to feet
- Show step-by-step calculation
- Provide beam angle adjustments
- Estimate lumens
Practical Applications
Flashlight Testing
Manufacturers often measure lux at 1 meter and convert to candela to rate beam intensity.
LED and Spotlight Design
Determine how focused or powerful a beam is.
Stage Lighting
Calculate required intensity for performers at specific distances.
Architectural Lighting
Ensure buildings and displays meet illumination standards.
Important Notes
- Distance must be measured in meters
- This formula assumes a point light source
- For wide beam sources, results may vary
- Reflection and ambient light can affect measurements
Frequently Asked Questions
Can I convert lux to candela without distance?
No. Distance is required because illuminance depends on how far the light travels.
Does beam angle affect the calculation?
Beam angle affects how light spreads, but the basic lux-to-candela formula relies primarily on distance.
What if distance is 1 meter?
At 1 meter:
cd = lux
$$
Lux and candela values become equal at 1 meter.
Why This Calculator Is Useful
✔ Helps engineers measure light performance
✔ Supports lighting compliance testing
✔ Simplifies photometric calculations
✔ Improves design accuracy
✔ Saves time during installations
Final Thoughts
A Lux to Candela Calculator bridges the gap between surface brightness and source intensity.
By applying a simple formula:
cd = lux \times distance^2
$$
You can accurately determine how strong a light source is in a given direction.
Whether you’re testing a flashlight, designing stage lighting, or planning architectural illumination, this calculator provides fast, reliable results.