Luminous Intensity Converter
Convert candela (cd), millicandela (mcd), hefnerkerze (HK), international candle.
Result
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Base Unit
Relative Value
*Diagram shows values relative to the selected base unit (Candela).
Unit Information
What is Candela (cd)?
The candela (symbol: cd) is the SI base unit of luminous intensity. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 10¹² Hz (green light, near peak human eye sensitivity) to be 683 when expressed in the unit lm·W⁻¹. Essentially, it measures how much light a source emits in a specific direction.
What is Millicandela (mcd)?
Millicandela (symbol: mcd) is a submultiple of the candela, equal to one-thousandth of a candela (1 cd = 1000 mcd). This unit is commonly used for specifying the luminous intensity of LEDs (Light Emitting Diodes), especially indicator LEDs or those used in small displays, where the intensity is relatively low compared to general lighting sources.
What is Hefnerkerze (HK)?
The Hefnerkerze or 'Hefner candle' was an early standard for luminous intensity developed in Germany in the late 19th century. It was based on the light produced by a specific type of lamp (the Hefner lamp) burning a specific fuel under controlled conditions. It is approximately equal to 0.903 candelas.
What is International Candle (cd_intl)?
'Candlepower' or the International Candle was an obsolete unit of luminous intensity. It was an attempt to standardize light measurement before the modern definition of the candela was established. It is approximately equal to 1.019 candelas.
Formulas
1 cd = 1000 mcd
One Candela is equal to 1000 Millicandela.
Lumens = Candelas × Solid Angle (sr)
The total light output (lumens) is the intensity (candelas) multiplied by the solid angle over which it is emitted.
1 cd_intl ≈ 1.019 cd
The historical International Candle is very close in value to the modern Candela.
Key Reference Points
- A common wax candle: ~1 candela (cd).
- A typical indicator LED: ~5-50 millicandela (mcd) (can vary widely).
- A high-brightness LED for lighting: Can be tens or hundreds of candelas (cd) (depending on beam angle).
- Automotive headlight (high beam): Can be tens of thousands of candelas (kcd) in the main beam direction.
- A lighthouse beam: Can exceed 1,000,000 cd (1 megacandela).
- A 800 lumen light bulb emitting light in all directions has an average intensity of about 64 cd.
- An 800 lumen spotlight focusing its light into a narrow beam can have an intensity of over 15,000 cd in the center of that beam.
- A typical laser pointer has a low total light output (lumens) but a very high luminous intensity (candelas) due to its extremely narrow beam.
- A bare fluorescent tube has a low intensity in any single direction but a high total lumen output.
- The sun's luminous intensity is about 2.8 × 10²⁷ cd.
Did You Know?
The candela was originally based on the light emitted by a standard wax candle, hence its name (candela is Latin for candle). Early units like 'candlepower' were efforts to standardize this. The International Candle, adopted in 1909, was an attempt to create a more reproducible standard before the modern definition of the candela was established based on physical constants.
The luminous intensity of a light source can vary significantly depending on the direction and its beam angle. A source with a narrow beam angle will concentrate its light, resulting in a higher candela value within that beam.
LED technology has allowed for very high luminous intensities from small sources. This is why LEDs are effective in applications like traffic signals, automotive lighting, and high-powered flashlights.
An isotropic source is a theoretical point source that emits light uniformly in all directions. The relationship between its total luminous flux (in lumens) and its luminous intensity (in candela) is Lumens = 4π × Candelas.
The candela is a photometric unit, meaning it is weighted by the luminosity function, which models the average sensitivity of the human eye to different wavelengths of light. Our eyes are most sensitive to green light around 555 nm.
There is no simple conversion from watts (radiometric power) to candelas (photometric intensity). The conversion depends on the spectral distribution of the light source and the luminosity function of the eye. A green laser is very efficient at producing candelas from watts, while an infrared heat lamp produces very few.
Lighthouses use powerful lamps combined with large lenses (like Fresnel lenses) to concentrate light into a narrow, intense beam that can be seen for many miles. Their intensity can be in the range of millions of candelas.
This is a path on a chromaticity diagram that represents the color of an incandescent black-body radiator as its temperature changes. It's fundamental to the definition of the candela and understanding light source color.
The human eye is incredibly sensitive and can detect a luminous intensity equivalent to a single candle flame from as far as 30 miles (48 km) away on a clear, dark night.
The effectiveness of a signal lamp, like those used on ships or in air traffic control towers, is measured by its luminous intensity. A high candela rating ensures the signal is visible and distinguishable over long distances.
Invented by Augustin-Jean Fresnel, this type of lens can be made much thinner and lighter than a conventional lens of the same focal length. It's used in lighthouses and spotlights to collimate light from a source into a tight beam, massively increasing its luminous intensity.
Automotive headlight performance is regulated by standards that specify minimum and maximum luminous intensity values at various angles to ensure adequate illumination for the driver without causing glare for oncoming traffic.
Photometry (using units like candela) is the science of measuring light as perceived by the human eye. Radiometry (using units like watts per steradian) is the science of measuring electromagnetic radiation across the entire spectrum, regardless of human perception.
The apparent brightness of a star is measured by its apparent magnitude, but its intrinsic brightness is its luminous intensity. Stars are so far away that their intensity as measured on Earth is extremely low.
The Violle was a proposed unit of luminous intensity, defined as the light emitted by 1 square centimeter of platinum at its melting point. It was an an early attempt at a reproducible standard but was difficult to implement.
During manufacturing, LEDs are sorted or 'binned' based on their characteristics, including luminous intensity, color, and forward voltage. This ensures that LEDs used in a single product, like a large video screen, are visually consistent.
A goniophotometer is an instrument used to measure the directional light distribution of a source. It measures the luminous intensity at many different angles to create a complete picture of how the light is emitted, which is crucial for lighting design.
Lasers are classified based on their potential to cause eye damage. While this is related to their power (watts), the key danger is the very high luminous intensity (or more accurately, radiance) of the focused beam, which can instantly damage the retina.