Candela
The candela (/kænˈdɛlə/ or /kænˈdiːlə/; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous to radiant intensity, but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the luminous efficiency function, the model of the sensitivity of the human eye to different wavelengths, standardized by the CIE and ISO. A common wax candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured.
| candela | |
|---|---|
Photopic (black) and scotopic (green) luminous efficiency functions. The photopic includes the CIE 1931 standard (solid), the Judd–Vos 1978 modified data (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data (dotted). The horizontal axis is wavelength in nm. | |
| General information | |
| Unit system | SI |
| Unit of | luminous intensity |
| Symbol | cd |
| Conversions | |
| 1 cd in ... | ... is equal to ... |
| international candles | ≈ 1.02 cp |
| Hefner Kerze | ≈ 1.11 HK |
The word candela is Latin for candle. The old name "candle" is still sometimes used, as in foot-candle and the modern definition of candlepower.