Yeah you're confused. Now a lot of manufacturers of LEDs market models as the wattage rating of each diode times the number of diodes. So a lot of 300W lights are 100-3W LEDs but they aren't really running at 300W, more like a little over half of that. Though some do advertise more along the lines of actual watts. I'm doing a small 2x3 test grow using an area 51 xgs 190 that uses 190W on full force. This is my first round but I'm hoping it will compare to what I could accomplish with a 400 HPS.
The XGS should give you resultss in the same neighborhood as your 400W HPS, probably a little less, but pretty close.
Ohhhh I see. Well when I bought my grow tent it said to use with LED the recommended was 135w - 240w. Then I got to reading through the LED section and I was like like ehhh maybe 240w wouldn't be good enough. Lol
Let me guess, you have a tent from Gotham Hydro?
They would be the ones recommending LED lights in those wattages, as they correspond to the ones they sell.
Anyways, the minimum for flowering a tent like yours would be the light that gk skunky mentioned, the XGS-190 by Area 51.
Now depending on how big your budget is, and what you want your yield to be, you may want two units (XGS or SGS) for a 39"x39" area.
But for overall value, quality, and performance, we consider Area 51's LED lights to be the best bang for the buck (I use them myself).
Be wary of LED lights sold on ebay and amazon, they don't last long, and usually don't perform very well.
but thanks for the information you helped me a lot 
)