Luminous Intensity Converter
Convert between different luminous intensity units including candela, lumen/steradian, candle, hefner candle, and carcel unit.
Result
1 cd = 1 lm/sr
Understanding Luminous Intensity Units: Candela to Candlepower to Lumen per Steradian
Luminous intensity converters are essential tools for calculating light output, luminous flux per unit solid angle, and photometric intensity in lighting design, display technology, and photometry. Whether you're working with candelas (cd), lumen per steradian (lm/sr), candle (international), candle (German), candle (UK), decimal candle, pentane candle, hefner candle, carcel unit, bougie decimal, candlepower, or any of twelve luminous intensity units, understanding luminous intensity conversions is crucial for engineers, designers, and analysts in lighting design, display technology, automotive lighting, aerospace lighting, and photometric measurement industries.
Luminous intensity measurements quantify the light output per unit solid angle of a light source, representing directional light emission essential for light source characterization, lighting design, and photometric calculations. From low-intensity LEDs at 1-100 millicandela to high-intensity searchlights at 1,000,000+ candela, and from historical candle measurements to modern SI candela standards, this comprehensive converter supports twelve luminous intensity units with instant, accurate results for all your light output, luminous flux, and photometric intensity calculations across different measurement systems.
How to Convert Luminous Intensity Units: Formulas and Methods
Candela to Lumen per Steradian Conversions
Converting from candela (cd) to lumen per steradian (lm/sr) is exact, since 1 candela equals 1 lumen per steradian by definition in the SI system. For example, a luminous intensity of 100 cd equals 100 lm/sr. This relationship follows from the definition of candela as the luminous intensity in a given direction of a source emitting monochromatic radiation of frequency 540×10^12 Hz with a radiant intensity of 1/683 watt per steradian. These conversions are exact and commonly used in modern photometry.
Historical Candle Units and Conversions
Converting from candela to candle (international) is exact, since 1 candle (international) equals 1 candela by definition. Converting to candle (UK) multiplies by approximately 0.962, since 1 candle (UK) equals approximately 1.04 candela. Converting to candle (German), which historically used the Hefner candle standard, multiplies by approximately 0.901, since 1 candle (German) equals approximately 1.11 candela. These historical units reflect different national standards before the adoption of the international candela definition in 1948.
Hefner Candle and Carcel Unit Conversions
Converting from candela to Hefner candle multiplies by approximately 1.107, since 1 Hefner candle equals approximately 0.903 candela (defined using a Hefner lamp burning amyl acetate). Converting to carcel unit multiplies by approximately 0.104, since 1 carcel unit equals approximately 9.6 candela (defined using a Carcel lamp burning colza oil). These historical units were used in German and French photometry before standardization. Converting to candlepower (US) multiplies by approximately 1.019, since 1 candlepower equals approximately 0.981 candela.
Pentane Candle and Decimal Candle Conversions
Converting from candela to candle (pentane) is approximately 1:1, since pentane candles were designed to match the candela definition. Converting to pentane candle (10 candle power) divides by 10, since 1 pentane candle (10 candle power) equals 10 candela. Decimal candle and bougie decimal are equivalent to candela, with 1 decimal candle or 1 bougie decimal equaling 1 candela by definition. These units represent attempts to standardize luminous intensity measurements before the modern SI system.
Luminous Intensity Versus Luminous Flux and Illuminance
Luminous intensity (I, cd) measures light output per unit solid angle in a specific direction, while luminous flux (Φ, lm) measures total light output in all directions. Luminous flux relates to luminous intensity through integration over solid angle: Φ = ∫I dΩ. Illuminance (E, lux) measures luminous flux per unit area incident on a surface. Converting luminous intensity units helps engineers calculate light output, predict illumination patterns, and design lighting systems when working with different measurement systems and comparing international photometric standards.
Luminous Intensity Conversion Reference Table
| cd | lm/sr | candle (intl) | candle (UK) | hefner candle |
|---|---|---|---|---|
| 0.1 | 0.1 | 0.1 | 0.096 | 0.111 |
| 1 | 1 | 1 | 0.962 | 1.107 |
| 10 | 10 | 10 | 9.62 | 11.07 |
| 100 | 100 | 100 | 96.2 | 110.7 |
| 1000 | 1000 | 1000 | 962 | 1107 |
| 10000 | 10000 | 10000 | 9620 | 11070 |
Typical Luminous Intensity Values by Application
| Application | cd | lm/sr | Description |
|---|---|---|---|
| LED indicator | 1-100 mcd | 1-100 mcd | Status indicators |
| LED flashlight | 100-500 | 100-500 | Portable lighting |
| Car headlight | 1000-10000 | 1000-10000 | Automotive lighting |
| Stage spotlight | 10000-100000 | 10000-100000 | Theatrical lighting |
| Lighthouse beacon | 100000-1000000 | 100000-1000000 | Maritime navigation |
| Searchlight | 1000000+ | 1000000+ | High-intensity lighting |
| Candle flame | ~1 | ~1 | Historical reference |
| 60W incandescent bulb | ~70 | ~70 | General lighting |
Industry Applications and Use Cases
Lighting Design and Photometric Measurement
Lighting designers use luminous intensity measurements in candela to characterize light sources, optimize beam patterns, and ensure appropriate illumination in architectural and interior design. Typical luminous intensities range from 1-1,000,000+ candela for various lighting applications. Converting between candela, lumen per steradian, historical candle units, and candlepower helps designers work with international lighting standards, compare specifications, and design lighting systems when working with different measurement systems and equipment specifications.
Automotive Lighting and Safety
Automotive engineers use luminous intensity measurements in candela to design headlights, taillights, and signal lights for safety and visibility. Typical automotive luminous intensities range from 100-10,000 candela for various lighting components. Converting between luminous intensity units helps engineers work with international automotive lighting standards, compare specifications, and design lighting systems when developing new vehicle lighting technologies.
Display Technology and LED Applications
Display engineers calculate luminous intensities in candela to design LED displays, optimize viewing angles, and ensure appropriate brightness in consumer electronics and professional displays. Typical LED luminous intensities range from 1 millicandela to 10,000+ candela for various display applications. Converting between luminous intensity units helps engineers work with international display standards, compare specifications, and design displays when developing new display technologies.
Aerospace and Aviation Lighting
Aerospace engineers use luminous intensity measurements in candela to design cockpit displays, navigation lights, and cabin lighting for safety and visibility. Typical aerospace luminous intensities range from 10-100,000 candela for various lighting applications. Converting between luminous intensity units helps engineers work with international aerospace standards, compare measurements, and design lighting systems when developing new aircraft lighting technologies.
Frequently Asked Questions
What is luminous intensity and how is it different from luminous flux?
Luminous intensity (I, cd) measures light output per unit solid angle in a specific direction, while luminous flux (Φ, lm) measures total light output in all directions. Luminous intensity describes directional light emission, while luminous flux describes total light output. Converting luminous intensity units helps engineers quantify light output and compare measurements when designing lighting systems and displays.
How do I convert candela to lumen per steradian?
cd equals lm/sr exactly, since 1 candela equals 1 lumen per steradian by definition in the SI system. For example, 100 cd equals 100 lm/sr. This relationship follows from the definition of candela as the luminous intensity in a given direction. This conversion is exact and commonly used in modern photometry.
How to convert candela to candle (international)?
cd equals candle (international) exactly, since 1 candle (international) equals 1 candela by definition. For example, 100 cd equals 100 candle (international). The candle (international) was the predecessor to the modern SI candela definition. This conversion is exact and commonly used in historical photometry.
How to convert hefner candle to candela?
Multiply hefner candle by 0.903 to get cd, since 1 Hefner candle equals approximately 0.903 candela (defined using a Hefner lamp burning amyl acetate). For example, 1 hefner candle equals approximately 0.903 cd. Hefner candles were used in German photometry before standardization.
What's the relationship between luminous intensity and illuminance?
Luminous intensity (I, cd) measures light output per unit solid angle, while illuminance (E, lux) measures luminous flux per unit area incident on a surface. For point sources, E = I/r², where r is distance. Converting luminous intensity units helps engineers calculate illumination levels and design lighting systems when working with different measurement systems.
How to convert carcel unit to candela?
Multiply carcel unit by 9.6 to get cd, since 1 carcel unit equals approximately 9.6 candela (defined using a Carcel lamp burning colza oil). For example, 1 carcel unit equals approximately 9.6 cd. Carcel units were used in French photometry before standardization.
How is luminous intensity measured in practice?
Luminous intensity is measured using photometers or goniophotometers that detect light output at specific angles through filters matching the human eye's spectral sensitivity. Measurements are performed at defined distances and angles, and luminous intensity is calculated from photometric readings. Converting luminous intensity units helps engineers interpret measurements and compare data across different measurement instruments and international standards.
How to convert candlepower to candela?
Multiply candlepower by 0.981 to get cd, since 1 candlepower (US) equals approximately 0.981 candela. For example, 100 candlepower equals approximately 98.1 cd. Candlepower was used in US photometry before standardization.
How accurate are luminous intensity conversions?
Our converter uses exact mathematical relationships with 10-decimal precision for SI units. cd to lm/sr: exact 1:1 conversion. cd to candle (international): exact 1:1 conversion. Historical units like hefner candle and carcel unit use approximate conversions based on historical definitions. These conversions ensure precision for scientific and engineering applications in photometry and lighting design.
How does luminous intensity relate to beam angle?
Luminous intensity describes light output in a specific direction, while beam angle describes the angular spread of light emission. For uniform sources, total luminous flux relates to peak luminous intensity through beam angle: Φ ≈ I × Ω, where Ω is solid angle. Converting luminous intensity units helps engineers calculate beam patterns and design lighting systems when working with different measurement systems.
How to convert pentane candle to candela?
Pentane candle equals cd approximately 1:1, since pentane candles were designed to match the candela definition. Pentane candle (10 candle power) equals 10 cd. For example, 1 pentane candle equals approximately 1 cd, and 1 pentane candle (10 candle power) equals 10 cd. Pentane candles were used in photometry before standardization.
How is the candela defined in the SI system?
The candela is defined as the luminous intensity in a given direction of a source emitting monochromatic radiation of frequency 540×10^12 Hz with a radiant intensity of 1/683 watt per steradian. This definition links luminous intensity to radiant intensity through the human eye's spectral sensitivity. Converting luminous intensity units helps engineers work with the SI system and compare measurements across different photometric standards.
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