Good question digimidgi! Honestly, I really don't know! I was a little confused and annoyed the first time I figured it out. There are other manufacturers that do the same type of thing. IE. 357 magnum light, you would think it would draw at least 300 watts of power, but it actually only draws 180 watts. My bud, DUNIT used two of these to grow 9 purple Kush with a combined power draw of 360 watts! He was able to pull over 1 gram per watt with sticky icky beautiful buds. After seeing his grow journals I learned that it doesnt really matter about how much power your light draws, because it is a lot different than HID. The plants really thrive off the different spectrums that LED uses. I wanted to grow bigger and bushier plants so I chose to use 1000 watts of LED which the power draw is 608 watts. I figured either go big or go home, and I wanted to makes sure I had a successful grow. I probably would have been ok with 1 500w or better yet 1 500w and 1 240 blackstar. I wanted all my plants to be equal, so I decided to use 2 500s.