Candlepower

Candlepower is a unit of luminous intensity, historically defined by a standard candle and now generally treated as equivalent to the candela.

Luminous intensity: The amount of light emitted by a source in a particular direction, measured per unit solid angle. Candlepower names a unit for this directional quantity.
Jules Violle: A French physicist who proposed a luminous-intensity standard based on platinum at its melting point. His high-temperature reference helped move standards beyond ordinary candles.
Flashlight: A portable battery-powered device that directs light from an electric lamp or LED. Some flashlight specifications still use candlepower to describe beam intensity.
Lumen: The SI unit of luminous flux, representing the total visible light emitted by a source. A lumen measures total light output, whereas candlepower measures directional intensity.
Candela: The SI base unit of luminous intensity. The candela replaced candlepower as the standardized unit.
Hefner lamp: A standardized amyl-acetate lamp used as a luminous-intensity reference in late nineteenth-century Europe. It was one of the competing practical standards that candlepower displaced.
Beam candlepower: A measure of a lamp’s luminous intensity in the direction of its strongest beam. It is a specialized form of candlepower used for focused lights.
Lux: The SI unit of illuminance, equal to one lumen per square metre. Lux measures light falling on an area rather than light emitted in a direction.
Photometry: The science of measuring light as weighted by the human visual response. Candlepower belongs to photometry’s system of light measurement.
International candle: An early twentieth-century international standard of luminous intensity based on selected electric lamps. It replaced less consistent candle-based references before the candela.

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