Brooke Martin
Candlepower, also known as candela, is a unit of measurement for luminous intensity, or light intensity. It is derived from the amount of light that a candle of a specific size emits. In modern usage, candlepower is sometimes used interchangeably with the term candela, which is considered a more standard unit for light intensity. While there is no direct conversion from candlepower to watts, as watts are a measurement of resistance, a candle's wattage can be calculated by multiplying the rate at which it burns (in grams per second) by the energy in a gram of its material (in joules). A candle burning 2 thousandths of a gram per second of spermaceti, a material derived from sperm whales, would have a power of about 80 watts.
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What You'll Learn
Candlepower vs candela
Candlepower, also known 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. In 1860, the Metropolitan Gas Act defined candlepower as the light produced by a pure spermaceti candle weighing 1/6 pound (76 grams) and burning at a rate of 120 grains per hour (7.8 grams per hour). Spermaceti is a material derived from sperm whale heads that was historically used to make high-quality candles.
In 1948, the international unit (SI) candela replaced candlepower. One candlepower unit is approximately 0.981 candela. In modern usage, candlepower is sometimes used as a synonym for candela, with a direct 1:1 equivalence. However, "candlepower" is largely considered an obsolete term. Candlepower is still used in certain contexts, such as in the California Vehicle Code to define legal requirements for headlamps and other lamps.
Candela, or candela power, is a measure of luminous intensity. It is defined as the luminous intensity of a blackbody at the freezing point of platinum, which is approximately 58.9 international candles per square centimetre. A torch with 300,000 candela is considered a good thrower.
While candlepower and candela are both units of luminous intensity, they differ in their base references. Candlepower is based on the light emitted by a specific type of candle, while candela is defined relative to the luminous intensity of a blackbody at a specific temperature. Additionally, candela is the modern SI unit, replacing candlepower in 1948.
It is important to note that candlepower and watts are not directly interchangeable as units of measurement. Candlepower is an expression of lumens, while watts are a measurement of resistance. To convert watts to candlepower, one must multiply the wattage by the performance factor of the bulb and then divide by 12.57. For example, to convert 500 watts to candlepower, you would first determine the performance factor of the bulb, which is given as 2.5 lumens/watt. Then, you would multiply 500 watts by 2.5 lumens/watt, resulting in 1250 lumens. Finally, you would divide 1250 lumens by 12.57 to get the candlepower, which is approximately 99.44.
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Candlepower is luminous intensity
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 historical candlepower is equal to 0.981 candelas. In modern usage, candlepower is 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 (7.8 grams per hour). Spermaceti is a material from the heads of sperm whales that was once used to make high-quality candles.
In 1937, the international candle was redefined against the luminous intensity of a blackbody at the freezing point of liquid platinum, which was to be 58.9 international candles per square centimetre. In 1948, the international unit (SI) candela replaced candlepower. One candlepower unit is about 0.981 candela. In general modern use, a candlepower now equates directly (1:1) to the number of candelas—an implicit increase from its old value.
Candlepower is largely an obsolete term, but people still sometimes use it to describe the luminous intensity of high-powered flashlights and spotlights. Narrow-beamed lights of all sorts can have very high candlepower specifications because candlepower measures the intensity of the light on a target, rather than the total amount of light it emits. A given lamp has a higher candlepower rating if its light is more tightly focused.
Candlepower is still used today in law. For example, it is presently used in the California Vehicle Code to define the legal requirements for headlamps and other lamps, including accessory lamps.
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Watts are a measurement of resistance
Candlepower, also known as candela, is a unit of measurement for luminous intensity. One million candlepower is equivalent to 12,566,370 lumens. However, it is difficult to determine how many watts this is, as this would depend on the type of light bulb and its performance factor. For example, a 35-watt handheld halogen spotlight is about one million candlepower, which would be roughly equivalent to a 25-watt LED or 20-watt HID.
Watts are a measurement of power, specifically electric power, or the rate of electrical work. Watts can be calculated by multiplying voltage by the current. In other words, watts measure how much work can be done in a certain amount of time. For example, a 100-watt light bulb consumes 100 watts of power per hour.
However, watts are also related to resistance, which is measured in ohms. The higher the resistance, the more difficult it is for electricity to flow. Resistance is the strength of a given wire to oppose the flow of electrons. The relationship between watts, voltage, current, and resistance can be calculated using Ohm's Law: watts = volts x amps x ohms. Therefore, while watts are not solely a measurement of resistance, they are influenced by it.
In conclusion, while candlepower and watts are both units of measurement related to light and electricity, they are not interchangeable. Candlepower measures luminous intensity, while watts measure power. Watts are influenced by resistance, but they are also dependent on voltage and current.
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Candlepower is derived from candle light intensity
Candlepower, also known as the candela, 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 term candlepower was originally defined in the United Kingdom by the Metropolitan Gas Act 1860 as the light produced by a pure spermaceti candle that weighed one-sixth of a pound (76 grams) and burned at a rate of 120 grains per hour (7.8 grams per hour). Spermaceti is a material from the heads of sperm whales that was historically used to make high-quality candles.
In 1909, several agencies, including representatives from France, the United Kingdom, the United States, and Germany, met to establish an international standard for the candle. The majority of the group decided to redefine the candle in terms of an electric lamp with a carbon filament. However, the Germans disagreed and based their definition on the output of a Hefner lamp.
In 1921, the Commission Internationale de l'Eclairage (CIE) or the International Commission for Illumination redefined the international candle in terms of a carbon filament incandescent lamp. Later, in 1937, the international candle was again redefined against the luminous intensity of a blackbody at the freezing point of liquid platinum, which was set at 58.9 international candles per square centimetre.
In 1948, the international unit (SI) candela replaced candlepower. One candlepower unit is approximately 0.981 candela. In modern usage, candlepower is sometimes used as a synonym for candela, and it is equivalent to one lumen per steradian. The candela measures the luminous power per unit solid angle emitted by a light source in a particular direction.
While the term candlepower is considered obsolete, it is still used to describe the luminous intensity of high-powered flashlights and spotlights. Candlepower measures the intensity of light on a target rather than the total amount of light emitted.
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Candlepower and watts are not interchangeable
On the other hand, watts are a measurement of electrical energy poured into a light source, or power (volts x amperes) input into an electric lamp. Watts tell us nothing about light output, as some light sources consume energy more efficiently than others. For example, a 35-watt handheld halogen spotlight is about one million candlepower, which would be roughly equivalent to a 25-watt LED or 20-watt HID.
To calculate candlepower from watts, one must multiply the wattage by the performance factor of the bulb, then divide by 12.57. This is a tricky calculation because different bulb designs have different efficiencies.
While candlepower and watts are not interchangeable, they can be compared by looking at a bulb's lumens-per-watt performance, or how much light is produced for each watt of energy consumed. Lumens are a metric used to measure the total amount of light produced by a source or the amount of light falling on a surface.
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Frequently asked questions
One million candle power is approximately 35 watts.
In the UK, the Metropolitan Gas Act of 1860 defined candlepower as the light produced by a pure spermaceti candle that weighs 1⁄6 pound (76 grams) and burns at a rate of 120 grains per hour (7.8 grams per hour).
Candlepower is now defined as the luminous intensity of a blackbody at the freezing point of liquid platinum, which is 58.9 international candles per square centimetre.
To calculate candle power from watts, multiply the wattage by the performance factor of the bulb, then divide by 12.57.
A candle gives out about 80 watts of power, but only 0.05% of this energy is emitted as visible light, which is equivalent to the brightness of a 4-watt light bulb.
