What does candlepower mean?
Candlepower is a unit of luminous intensity — a measure of how bright a light source appears along a given direction. It originated in the nineteenth century, when the output of lamps was compared with that of a standard candle made from specified wax; the term thus predates modern photometry. Candlepower served scientists and engineers for decades, appearing in the specifications of lighthouses, searchlights, and early electric lamps, before being formally superseded by the candela, the SI base unit adopted in the mid-twentieth century. One candlepower corresponds to slightly less than one candela, so the two are often treated as interchangeable in casual use. Today the word survives mostly in historical texts, technical literature on lighting, and informal descriptions of powerful lamps, such as flashlights or vehicle spotlights marketed by their 'candlepower' rating. For readers, it offers a vivid reminder of an era when even scientific measurement was anchored to everyday objects like a humble burning candle.
nounA former unit of luminous intensity, originally defined as the light emitted by a standard candle and later standardized internationally as the candela (one candlepower ≈ 0.981 candela).
- A unit of luminous intensity based on the light of a standard candle, now largely superseded by the SI unit candela.
- Informally, the brightness or illuminating power of a lamp or light source.
"The old lighthouse manuals rated the lamp's beam in thousands of candlepower."
"The searchlight on the coast guard vessel was advertised as producing ten million candlepower."
"Early automobile headlights were graded by their candlepower rather than by lumens."
The plural is rare, since candlepower typically functions as a unit name rather than a countable object; measurements are usually given as a single figure followed by the unit.
"The catalog compared lamps ranging from a few hundred to several thousand candlepowers."
Before lasers and LEDs, engineers measured a light's strength by comparing it to actual burning candles — hence 'a million candlepower' literally means 'as bright as a million candles.'
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of candlepower
Candlepower is a straightforward English compound formed from 'candle' and 'power', coined during the nineteenth century when the brightness of lamps was standardized against a candle of defined composition and burn rate. The word 'candle' itself derives from Old English 'candel', borrowed from Latin 'candela', meaning a taper or wax light, which in turn comes from 'candere', 'to shine or glow white'. Its closest relative in modern measurement vocabulary is the candela, the SI successor to candlepower, while other cognates sharing the same Latin root include 'chandler' (a candle seller) and 'incandescent' (glowing with heat).
How candlepower is actually used
Candlepower is chiefly technical or historical in register, encountered in lighting engineering, lighthouse documentation, and older product specifications. In everyday modern usage it has been almost entirely replaced by the candela and related SI units.
Easily confused with candlepower
The candela is the modern SI unit of luminous intensity that replaced the candlepower, with one candlepower equal to roughly 0.981 candela.