Lux to Candela Calculator

How the Lux to Candela Calculator Works

The lux to candela calculator determines the luminous intensity (candela) of a light source based on the measured illuminance (lux) and the distance from the light source to the illuminated surface. This calculation is essential in lighting design, allowing professionals to assess how much light is emitted in a particular direction from a source.

By inputting the illuminance in lux and the distance in meters or feet, the calculator computes the luminous intensity in candelas. This aids in selecting appropriate lighting fixtures and ensuring adequate illumination levels for various applications.

Understanding Lux and Candela

Lux (lx) measures illuminance, indicating how much luminous flux (lumens) is spread over a given area. It represents the amount of light received per unit area. Candela (cd), on the other hand, measures luminous intensity, quantifying the amount of light emitted by a source in a particular direction.

In simpler terms, lux tells us how brightly a surface is illuminated, while candela tells us how intense the light source is in a specific direction. Understanding the relationship between these units is crucial for accurate lighting calculations.

Conversion Formula

To convert lux to candela, the following formulas are used, depending on the unit of distance:

• Distance in meters: candela = lux × (distance in meters)^2

• Distance in feet: candela = 0.09290304 × lux × (distance in feet)^2

These formulas illustrate that luminous intensity increases with the square of the distance from the light source, emphasizing the importance of accurate distance measurements in lighting design.

Practical Examples

Example 1:

A surface is illuminated with 500 lux, and the distance from the light source is 2 meters.

Using the formula:

candela = 500 × (2)^2 = 500 × 4 = 2000 cd

Therefore, the luminous intensity of the light source is 2000 candelas.

Example 2:

A surface is illuminated with 300 lux, and the distance from the light source is 10 feet.

Using the formula:

candela = 0.09290304 × 300 × (10)^2 = 0.09290304 × 300 × 100 = 2787.09 cd

Therefore, the luminous intensity of the light source is approximately 2787.09 candelas.

Why Can't Lux Be Directly Converted to Candela Without Distance?

Lux and candela measure different aspects of light. Lux quantifies the illuminance on a surface, while candela measures the luminous intensity emitted by a source. Without knowing the distance between the light source and the illuminated surface, it's impossible to accurately convert lux to candela, as the illuminance decreases with the square of the distance from the source.

How Does Distance Affect the Conversion?

The illuminance (lux) on a surface is inversely proportional to the square of the distance from the light source. As the distance increases, the same amount of light spreads over a larger area, reducing the illuminance. Conversely, when calculating the luminous intensity (candela) from a known illuminance, the intensity increases with the square of the distance.

Illuminance and Luminous Intensity Comparison

Distance (m)	Illuminance (lux)	Luminous Intensity (cd)
1	100	100
2	100	400
3	100	900
4	100	1600
5	100	2500

This table demonstrates how, for a constant illuminance, the required luminous intensity increases with the square of the distance.

Tips for Accurate Conversion

• Measure Distance Precisely: Ensure accurate measurement from the light source to the surface.

• Consider Beam Angle: The spread of light affects illuminance; narrow beams concentrate light, increasing lux.

• Account for Reflective Surfaces: Surfaces that reflect light can alter actual illuminance levels.

• Use Consistent Units: Stick to either meters or feet throughout your calculations to maintain consistency.

By understanding the relationship between lux and candela and utilizing the appropriate formulas, you can effectively design and assess lighting setups for various applications.