Candela to Lux Calculator

Understanding Candela to Lux Conversion

Converting between candela and lux is essential for lighting design, photography, and illumination engineering. While candela measures luminous intensity (how bright a light source appears), lux measures illuminance (how much light falls on a surface). Our free online calculator makes this conversion simple and accurate.

What is Candela?

Candela (cd) is the SI unit of luminous intensity, measuring how much light a source emits in a particular direction. It's one of the seven base units in the International System of Units. One candela represents the luminous intensity of a light source that emits monochromatic radiation of frequency 540×10¹² hertz with a radiant intensity of 1/683 watt per steradian in that direction.

What is Lux?

Lux (lx) measures illuminance, which is the amount of light falling on a surface per unit area. One lux equals one lumen per square meter. It's commonly used in lighting design to specify how much light is needed for different activities and environments.

The Conversion Formula

The relationship between candela and lux follows the inverse square law:

E(lx) = I(cd) / d²

Where:

E = Illuminance in lux (lx)
I = Luminous intensity in candela (cd)
d = Distance from the light source in meters (m)

Practical Applications

This conversion is crucial in various fields:

Architecture: Calculating proper lighting levels for buildings
Photography: Determining flash power and lighting setups
Automotive: Designing headlight systems and visibility standards
Industrial: Ensuring adequate lighting for safety and productivity
Entertainment: Stage lighting and film production

Common Lighting Levels

Understanding typical lux values helps in practical applications:

1-10 lx: Moonlight, emergency lighting
50-100 lx: General room lighting, corridors
300-500 lx: Office work, reading areas
1000+ lx: Retail displays, detailed work
10,000+ lx: Direct sunlight

Important Considerations

When using this calculator, keep in mind:

The formula assumes a point light source
The surface should be perpendicular to the light direction
Real-world factors like reflectors, lenses, and surface properties affect results
Multiple light sources require separate calculations

Frequently Asked Questions

What's the difference between candela and lux?

Candela measures luminous intensity (how bright a light source appears in a specific direction), while lux measures illuminance (how much light falls on a surface). Candela is about the light source itself, while lux is about the light received by a surface.

Why does illuminance decrease with distance?

This follows the inverse square law. As light spreads out from a point source, it covers a larger area, so the same amount of light is distributed over more space, resulting in lower illuminance per unit area.

Can I use this calculator for LED lights?

Yes, but be aware that LED specifications often list lumens rather than candela. You may need to convert lumens to candela first, or use a lumens-to-lux calculator if you have the beam angle.

How accurate is this calculator?

The calculator provides accurate results for theoretical calculations with point light sources and perpendicular surfaces. Real-world accuracy depends on factors like light source design, reflectors, and surface properties.

What units can I use for distance?

Our calculator supports meters, feet, inches, and centimeters. All distances are automatically converted to meters for the calculation, ensuring accurate results regardless of your preferred unit.

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