Understanding the conversion from candela to lux is essential for professionals working with lighting and photometry. This conversion translates luminous intensity into illuminance, crucial for accurate lighting design.
This article explores the fundamental concepts, formulas, practical tables, and real-world applications of candela to lux conversion. It provides detailed explanations and expert insights for precise calculations.
Artificial Intelligence (AI) Calculator for “Candela to Lux Conversion”
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Comprehensive Tables for Candela to Lux Conversion
Below are detailed tables showing the illuminance (lux) values derived from various luminous intensities (candela) at different distances. These tables are invaluable for lighting engineers, architects, and technicians.
| Luminous Intensity (cd) | Distance (m) | Illuminance (lux) |
|---|---|---|
| 100 | 1 | 100 |
| 100 | 2 | 25 |
| 250 | 1 | 250 |
| 250 | 3 | 27.78 |
| 500 | 1 | 500 |
| 500 | 2 | 125 |
| 750 | 1 | 750 |
| 750 | 3 | 83.33 |
| 1000 | 1 | 1000 |
| 1000 | 5 | 40 |
These values assume a point source emitting light uniformly in all directions, which is a common approximation in photometric calculations.
Fundamental Formulas for Candela to Lux Conversion
Converting candela (cd) to lux (lx) involves understanding the relationship between luminous intensity and illuminance. The core formula is derived from the inverse square law of light propagation.
- Illuminance (lux) = Luminous Intensity (candela) / Distance² (meters)
Expressed in HTML-friendly format:
Where:
- Illuminance (lx): The luminous flux incident per unit area, measured in lux (lumens per square meter).
- Luminous Intensity (cd): The luminous flux emitted by a source in a particular direction per unit solid angle, measured in candela.
- Distance (m): The distance from the light source to the point where illuminance is measured, in meters.
Additional considerations include:
- Solid Angle (steradian, sr): The three-dimensional angle over which the luminous intensity is measured.
- Luminous Flux (lumens, lm): Total light output emitted by the source, related to candela by the formula:Luminous Flux (lm) = Luminous Intensity (cd) × Solid Angle (sr)
For a point source emitting uniformly in all directions, the solid angle is 4π steradians, so total luminous flux is:
In practical applications, the illuminance at a surface perpendicular to the light source is calculated using the inverse square law, assuming no absorption or reflection losses.
Extended Formulas for Non-Perpendicular Surfaces and Angled Incidence
When the surface is not perpendicular to the light source, the angle of incidence (θ) affects the illuminance:
Where:
- θ (theta): The angle between the direction of the light and the normal (perpendicular) to the illuminated surface.
This formula accounts for the effective reduction in illuminance due to the angle of incidence, which is critical in architectural lighting and photometric design.
Real-World Examples of Candela to Lux Conversion
Example 1: Calculating Illuminance from a Street Lamp
A street lamp emits a luminous intensity of 1200 candela. Calculate the illuminance on the ground 8 meters below the lamp, assuming the light is directed straight down (θ = 0°).
- Given: Luminous Intensity (I) = 1200 cd, Distance (d) = 8 m, θ = 0°
- Formula: Illuminance (E) = I / d²
Step 1: Calculate distance squared:
Step 2: Calculate illuminance:
The ground directly beneath the lamp receives 18.75 lux of illuminance.
Example 2: Illuminance on an Angled Surface from a Spotlight
A spotlight has a luminous intensity of 500 candela. The light hits a surface 3 meters away at an angle of 45°. Calculate the illuminance on the surface.
- Given: I = 500 cd, d = 3 m, θ = 45°
- Formula: E = (I × cos θ) / d²
Step 1: Calculate distance squared:
Step 2: Calculate cos 45°:
Step 3: Calculate illuminance:
The surface receives approximately 39.28 lux of illuminance from the spotlight.
Additional Technical Considerations in Candela to Lux Conversion
While the inverse square law provides a fundamental basis for conversion, real-world scenarios often require adjustments for:
- Beam Angle and Distribution: Real light sources emit light over specific beam angles, affecting the distribution of luminous intensity.
- Reflectance and Absorption: Surfaces may reflect or absorb light, altering the effective illuminance.
- Atmospheric Attenuation: In outdoor applications, atmospheric conditions can reduce illuminance.
- Extended Sources: For sources that are not point-like, geometric factors and source size must be considered.
Advanced photometric calculations often use software tools and photometric data files (e.g., IES files) to model these effects accurately.
Standards and Guidelines for Photometric Measurements
Professional lighting design and measurement adhere to international standards, including:
- ISO 8995-1:2002 (CIE S 008/E:2001) – Lighting of Work Places – Part 1: Indoor
- IES Lighting Handbook – Illuminating Engineering Society guidelines
- CIE Publications – International Commission on Illumination standards
These documents provide authoritative methodologies for measuring and converting photometric quantities, ensuring consistency and accuracy.
Summary of Key Points for SEO Optimization
- Clear explanation of candela and lux units and their relationship.
- Detailed formulas with variable definitions and practical interpretations.
- Extensive tables with real-world values for quick reference.
- Step-by-step examples demonstrating practical applications.
- Consideration of advanced factors affecting conversion accuracy.
- References to official standards and authoritative sources.
By mastering candela to lux conversion, lighting professionals can design efficient, compliant, and effective lighting systems tailored to specific environments.