It's not so much about watts as how much usable energy is delivered to the plants. If you look up PAR and read some stickies in the Lighting part of the forum you will find a ton of info and discussions on the subject.
Many people on TPT use Finnex LED lights with great results - if you search the forum you will find a lot of pictures and testimonials. Good light and a good company.
Courtesy * Integrity * Perseverance * Indominable Spirit * and Self Control
Tenets of TKD