Comparing apples to apples, at last...

In the vast background noise written on the subject of LED vs other light sources comparison, this post is a little gem. James Alexander makes an excellent job at summarizing the issue with easy to understand day to day examples. Moreover, the cited numbers are among the most up-to-date at this point in time.

Although I disagree with him on the subjective matter of using 5 mm LEDs as a "real ligh" source, this is definitively worth reading.