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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 candla. [1]
One of the best-known of these standards was the English standard: candlepower. One candlepower was the light produced by a pure spermaceti candle weighing one sixth of a pound and burning at a rate of 120 grains per hour. Germany, Austria, and Scandinavia used the Hefnerkerze, a unit based on the output of a Hefner lamp. [4]
The old light used a 120 volt, 300 watt lamp, giving 1700 candlepower. The new light, even though it uses a slightly smaller lamp, 32 volt, 250 watt, will give 9000 candlepower, due to the increased efficiency of the filament and the removal of the green shade. The fog signal is a single tone diaphone which emits 1 blast every 15 seconds.
The 26th General Conference on Weights and Measures (CGPM) redefined the candela in 2018. [10] [11] The new definition, which took effect on 20 May 2019, is: The candela [...] is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 10 12 Hz, [a] K cd, to be 683 when expressed in the unit lm W −1, which is equal to cd sr W −1 ...
10 32: 1.23 × 10 32 W astro: approximate luminosity of Deneb: 10 33: 1.26 × 10 33 W astro: approximate luminosity of the Pistol Star, an LBV which emits in 10 seconds the Sun's annual energy output 1.79 × 10 33 W astro: approximate luminosity of R136a1, [72] a massive Wolf-Rayet star and the most luminous single star known 2.1 × 10 33 W
lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to radiant flux: Luminous efficacy (of a source) η [nb 3] lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to power consumption Luminous efficiency, luminous coefficient V: 1: Luminous efficacy normalized by the maximum possible efficacy See also:
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Luminous efficacy can be normalized by the maximum possible luminous efficacy to a dimensionless quantity called luminous efficiency.The distinction between efficacy and efficiency is not always carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed in lumens per watt, or "efficacies" expressed as a percentage.