Lumens (luminous flux) is the amount of light that humans see. If you want to measure what a plant sees, you need to measure radiant flux.

You can veg with anything. The best wavelength for veg is, well look at the chart. You cannot bud with anything. It must be the proper wavelength or you do little better than vegging. You can have thousands of LED's, several CFL's, or one HPS give you the same yield. Use whatever is the best for your situation. Just choose the proper color for the stage of development your plants are in.