I have always found the [Beer-Lambert law](http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law) written in terms of light intensity, but what are the units of that light intensity?

When related to light, some people talk about cd, or W/cm/cm... What are the right units?

If they are W/cm/cm, could the Beer-Lambert law be rewritten in terms of power?