Thunderfirst, welcome to confusing marketing.
Growing plants requires photons(just a unit of measurement) of light to grow plants. The confusion starts when we try to estimate how many photons of light a fixture can produce from each watt of electricity consumed. The efficiency of a light source has a huge impact on producing light(photon/watt)-this is where using power density(watts/sq ft) can help you estimate if you have enough intensity to grow good flower. For lower efficiency lights like CFL's, at least 50 w/sq ft. HID fixture(HPS,MH,CMH) 40-50 w/sq ft. Top-tier led's like a QB can hit that same light level at 30 w/sq ft.