Candela to Lux Calculator

How the Candela to Lux Calculator Works

The candela to lux calculator determines the illuminance (lux) on a surface based on the luminous intensity (candela) of a light source and the distance from the source to the surface. This calculation is essential for lighting design, photography, and ensuring adequate illumination in various environments.

By inputting the luminous intensity in candelas and the distance in meters or feet, the calculator computes the illuminance in lux. This helps users understand how bright a surface will appear under a specific light source at a given distance.

Understanding Candela and Lux

Candela (cd) measures the luminous intensity, indicating how much light is emitted in a particular direction. Lux (lx), on the other hand, measures illuminance, representing how much luminous flux is spread over a given area. In simpler terms, candela quantifies the source's strength, while lux indicates how bright a surface will be when illuminated by that source.

For example, a flashlight with a high candela rating emits a focused beam of light, making it appear brighter in a specific direction. However, the lux value will depend on how that light spreads over a surface area at a certain distance.

The Formula for Conversion

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

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

• Distance in feet: lux = 10.76391 × candela / (distance in feet)^2

These formulas illustrate that illuminance decreases with the square of the distance from the light source, emphasizing the importance of proximity in lighting design.

Practical Examples

Example 1:

A light source emits 100 candelas and is positioned 2 meters away from a surface.

Using the formula:

lux = 100 / (2)^2 = 100 / 4 = 25 lux

This means the surface receives an illuminance of 25 lux.

Example 2:

A spotlight with a luminous intensity of 500 candelas is 10 feet away from a wall.

Using the formula:

lux = 10.76391 × 500 / (10)^2 = 5381.955 / 100 = 53.82 lux

The wall receives approximately 53.82 lux of illuminance.

Is Lux the Same as Candela?

No, lux and candela measure different aspects of light. Candela quantifies the intensity of light emitted in a specific direction, while lux measures how much of that light illuminates a surface area. Therefore, while related, they serve distinct purposes in lighting measurements.

Why Does Distance Affect Lux?

Illuminance (lux) decreases with the square of the distance from the light source due to the dispersion of light over a larger area. As you move further from the source, the same amount of light spreads over a broader surface, reducing the intensity per unit area.

Illuminance Values for Common Environments

Environment	Recommended Lux
Office Work	300–500 lx
Classroom	300–750 lx
Hospital Operating Room	1000–2000 lx
Supermarket	750–1000 lx
Residential Living Room	100–300 lx
Street Lighting	10–20 lx
Full Daylight (Indirect)	10,000–25,000 lx
Direct Sunlight	32,000–100,000 lx

These values serve as guidelines for designing lighting systems that meet the specific needs of various environments.

Tips for Accurate Calculations

• 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 candela and lux, and utilizing the appropriate formulas, you can effectively design and assess lighting setups for various applications.