Chloe Adams
Candlepower (cp or CP) is a unit of measurement for luminous intensity, expressing levels of light intensity relative to the light emitted by a candle of specific size and constituents. The unit was originally defined in the United Kingdom by the Metropolitan Gas Act 1860, as the light produced by a pure spermaceti candle weighing 1/6 of a pound and burning at a rate of 120 grains per hour. In modern usage, candlepower is sometimes used as a synonym for candela, which is the modern unit of luminous intensity. The term candela comes from the Latin word for candle. While candlepower and candela are used interchangeably, they are not equal, with 1 candlepower being equal to 0.981 candelas. This unit of measurement is important for understanding the brightness of light sources, such as flashlights, and how they are marketed and sold to consumers.
Candlepower vs Candela
| Characteristics | Values |
|---|---|
| Candlepower (abbreviation) | cp or CP |
| Candela (abbreviation) | cd or CD |
| 1 candlepower | 0.981 candelas |
| 1 candela | 12.57 lumens |
| 1 lumen | 0.08 candela |
| Metric prefix for candela | millicandela (mcd) for 10^-3 candela |
| Historical definition of candlepower | Light produced by a pure spermaceti candle weighing 1/6 pound and burning at 120 grains/hour |
| Modern definition of candlepower | Synonymous with candela |
| Candela definition | Luminous efficacy of monochromatic radiation of frequency 540x1012 Hz, Kcd, to be 683 in unit lm W-1 |
| Candela definition (alternate) | Luminous intensity, in the perpendicular direction, of a surface of 1/600 000 square metre of a black body at the temperature of freezing platinum under a pressure of 101 325 newtons per square metre |
| Beam distance | Length of light projection until brightness falls below 0.25 lux (equivalent to brightness of full moon) |
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What You'll Learn
Candlepower is a unit of measurement for luminous intensity
Candlepower, abbreviated as cp or CP, is a unit of measurement for luminous intensity. It measures light intensity relative to the light emitted by a candle of a specific size and composition. The standard candlepower is defined as the light produced by a pure spermaceti candle weighing one-sixth of a pound and burning at a rate of 120 grains per hour (7.8 grams per hour). Spermaceti is a material derived from the heads of sperm whales, which was historically used to make high-quality candles.
In 1948, the international unit (SI) candela replaced candlepower as the standard unit for luminous intensity. One candlepower is approximately equal to 0.981 candelas. Despite this, the term "candlepower" is still sometimes used in modern contexts, particularly when describing the luminous intensity of high-powered flashlights and spotlights.
The candela (cd) is the standard unit for measuring luminous intensity in the International System of Units (SI). It measures the luminous power per unit solid angle emitted by a light source in a particular direction. The adoption of the candela as the standard unit for luminous intensity was driven by the need for a consistent and reliable standard across different countries. Before 1948, various standards for luminous intensity were in use, often based on the brightness of a "standard candle" or the illumination from a specific type of lamp.
The definition of the candela has been refined over time to improve accuracy and address challenges in practical implementation. The most recent definition, established by the 26th General Conference on Weights and Measures (CGPM) in 2018, took effect on May 20, 2019. This definition specifies the luminous efficacy of monochromatic radiation of a particular frequency, which corresponds to a wavelength of about 555 nanometers in the visible spectrum near green. This frequency range is where the human eye exhibits the highest sensitivity under bright conditions.
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1 candlepower = 0.981 candelas
Candlepower, abbreviated as cp or CP, is a unit of measurement for luminous intensity. It expresses levels of light intensity relative to the light emitted by a candle of specific size and constituents. The unit was originally defined in the United Kingdom by the Metropolitan Gas Act 1860 as the light produced by a pure spermaceti candle weighing one-sixth of a pound and burning at a rate of 120 grains per hour. Spermaceti is a material derived from the heads of sperm whales, which was historically used to make high-quality candles.
The term "candela" is derived from the Latin word for candle. It is the modern unit of luminous intensity, which replaced the term "candlepower" in 1948. The candela is defined as the luminous intensity, in the perpendicular direction, of a surface of 1/600,000 square meters of a black body at the temperature of freezing platinum under a pressure of 101,325 newtons per square meter.
While the terms candlepower and candela are sometimes used interchangeably, they are not equal. One candlepower is equal to 0.981 candelas. This conversion factor allows for the conversion of candlepower to candelas and vice versa. For example, a flashlight with a light output of 200 lumens and a peak beam intensity of 25,000 candlepower would have a more focused beam than a flashlight with the same light output but a peak beam intensity of 12,000 candlepower.
Manufacturers of flashlights often use candlepower as a marketing tool, touting high candlepower values to attract consumers. However, it is important to note that candlepower only measures the brightness of a directed beam, while lumens measure the total light output. Therefore, when comparing flashlights, it is essential to consider both candlepower and lumens, as well as other factors such as beam distance and colour temperature, to gain a comprehensive understanding of the flashlight's performance.
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Candela is derived from the Latin word 'candela' meaning candle
The term "candela" is derived from the Latin word "candela", which means candle. The word "candela" is used interchangeably with "candlepower" to refer to a unit of measurement for luminous intensity. Candlepower expresses levels of light intensity relative to the light emitted by a candle of specific size and constituents.
The historical candlepower is equal to 0.981 candelas, with the modern definition of candlepower sometimes used as a synonym for candela. The term candlepower was originally defined in the United Kingdom by the Metropolitan Gas Act 1860 as the light produced by a pure spermaceti candle weighing one-sixth of a pound and burning at a rate of 120 grains per hour. Spermaceti, a material derived from sperm whale heads, was once used to make high-quality candles.
In 1948, the term "candela" was adopted as the new name for the unit formerly known as the "new candle", which had been proposed by the Commission Internationale de l'Éclairage (International Commission on Illumination) and the CIPM in 1937. The value of the new candle was chosen to resemble the earlier unit of candlepower, with the brightness of a full radiator at the temperature of solidifying platinum set at 60 new candles per square centimetre.
The candela, like other SI units, can be modified by adding a metric prefix that multiplies it by a power of 10, such as the millicandela (mcd) for 10^-3 candela. The unit is used to quantify the luminous intensity or the amount of light emitted by a lighting device in a specific direction.
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The candela unit was redefined in 2018
The candela, represented by the symbol 'cd', is the SI unit of luminous intensity. It measures the luminous power per unit of solid angle emitted by a light source in a particular direction. The word 'candela' is derived from the Latin word 'candela', which means candle. The unit candela was introduced in 1948 as a replacement for the term 'candle'.
The candela is a unique SI unit as it is highly dependent on human perception. It is the SI unit for photometry and should not be confused with the total light emitted by an object, which is given by lumen. The candela does not represent the entire amount of light shining from an object but only the amount of light perceived by the human visual system. It is not used for every type of electromagnetic radiation. For example, radio waves and X-rays are measured in watts of power.
The candela is also referred to as candlepower. Candlepower is a unit of measurement for luminous intensity. One candlepower is equal to 0.981 candelas. Consumers frequently use candlepower, whereas labs use candela when reporting specifications according to the FL1 standard.
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Lumens measure total light output, while candelas measure the brightness of a directed beam
Lumens and candelas are both units used to measure the luminous efficacy of lighting devices. However, they refer to different aspects of a lighting device. Lumens measure the total light output, while candelas measure the brightness of a directed beam.
Lumens refer to the total amount of light emitted by a lighting apparatus. The higher the lumens value, the greater the light emitted and the larger the area it can illuminate. Lumens are not affected by the reflector or direction of the light. Instead, they represent the sum total of all the light emitted in all directions. For example, a standard fluorescent light device that emits a wide-spread beam can have a rating of 1,700 lumens and 135 candelas. However, if the light emitted from this apparatus is narrowed to shine within a 20-degree beam, its candela value will increase to 18,000, while the lumen value remains the same.
Candelas, on the other hand, refer to the amount of light emitted by a lighting device in a particular direction. Candela is another word for candlepower, which was derived from the amount of light emitted by a candle of specific dimensions. Candlepower was replaced by the term candela in 1948, and one candela is approximately equal to the light produced by such a candle. Candelas are used to measure peak beam intensity, which describes the light's intensity in a specific direction. For instance, a light source with a reflector will have a higher candela value as the light is intensified in one direction, even though the light output remains unchanged.
The relationship between candelas and lumens can indicate how focused a light beam is. For example, a flashlight with a light output of 200 lumens and a peak beam intensity of 25,000 candelas will have a more focused beam than a flashlight with the same light output but a lower peak beam intensity of 12,000 candelas.
It is important to understand the difference between lumens and candelas when choosing lighting devices to ensure that you select the most suitable option for your needs and avoid being misled by retailers quoting impressive values that may not be relevant to your specific requirements.
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Frequently asked questions
Candlepower (abbreviated as cp or CP) is a unit of measurement for luminous intensity. It expresses levels of light intensity relative to the light emitted by a candle of specific size and constituents.
The candela is the modern unit of luminous intensity. The word candela is Latin for candle. One candela is approximately equal to the light that a candle with specific dimensions produces.
Lima is not a standard unit of measurement. However, 1 candlepower is equal to 0.981 candelas.
The candela value of a lighting device is concerned primarily with a focused beam of light. Candlepower measures the brightness of the directed beam.
