The unit of measure commonly used to describe the intensity of small LEDs is the millicandela (mcd), 1000 millicandela equals 1 Candela. The Candela rating is an expression of how much light is produced as measured at the light source. The candela is the Luminous Intensity, in a given direction, of a source of monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
The unit of measure commonly used for most other light sources is the Lumen. Lumens are units of Luminous Flux and they measure how much light actually falls on a surface. The Lumens from a light source is equal to the Luminous Intensity (Candelas) multiplied by the solid angle over which the light is emitted, taking into account the varying intensities in different directions. Because of the variations of beam intensity by direction in LEDs, as a practical matter there is no straight forward way to mathematically convert between Candelas and Lumens.