Lux, mcd (millacandella), and candella (candlepower-cd) are readily interchangable because they're intensity measurements. They're in ready use for directional light sources (such as LEDs) because they're easy to measure - point the center of the light source beam at the sensor and you've got an intensity measurement.
Lumens is total light output, and requires a much more expensive (and cantankerous) integrating sphere to measure.
There are simple forumula for converting mcd/cd X beam angle to lumens, but they're inaccurate since intensity varies over the beam profile and beam angles are generally quoted to half-intensity.
Whenever you see a light figure quoted a spherical candlepower, there's a constant it can be multiplied by to determine lumens accurately.