坎德拉（拉丁语：Candela），发光强度的单位，国际单位制七个基本单位之一，符号cd。1979年10月第十六届国际计量大会将坎德拉定义为：给定一个频率为540.0154×10 Hz的单色辐射光源（黄绿色可见光）与一个方向，且该辐射源在该方向的辐射强度为1/683W/sr，则该辐射源在该方向的发光强度为1坎德拉。1坎德拉的点状光源所发出的总光通量为4π流明。一支普通蜡烛的发光强度约为1cd。

中国早些时候，把每1瓦的白炽灯的发光强度称之为一支烛光，如25瓦的就称之为25支烛光。其原因是一只220V/100W的白炽灯发出的光通量约等于400π流明。换算下来每1W的发光强度差不多就是1cd。

The candela (/kænˈdɛlə/ or /kænˈdiːlə/; symbol: cd) is the SI base unit of luminous intensity; that is, luminous power per unit solid angle emitted by a point 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 standard luminosity function (a model of the sensitivity of the human eye to different wavelengths). A common 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.