With that particular light, you will need more than 1. SuperGreenLab only use 1 for setting up a teeny tiny seedling box. The wattage draw is only a maximum of 18W and coverage 15x15 cm2.
For your size of tent, you would likely need 4, and given they cost $35.99 (for UK) or $43.55 (for EU), you would be better off looking for a different light.
The "wattage" (LEDs tend to be sold as equivalent wattage to HPS, as opposed to true wattage draw) would be between 600W and 1000W.
If you can, get 1 that is Full Spectrum Sunlike (not Blurple) and with a dimmer.
Check out the forums here for
reviews and
recommendations, then...
Look around on {cough}Amazon/eBay{cough}, and once you see one you like, search for the companies own website to see if they sell/deliver in your country (I don't know if you're EIRE or NI), where you may even be able to get it cheaper.
For example, I decided on a Spider Farmer SF1000. On "Glamazon", they wanted £179.99. I went to Spider Farmer's official website, followed a link to their UK site, and it was only £119.99 with free delivery from UK warehouse (no import fees and had a UK plug). I even got a further £5.99 off thanks to a discount code, so I only paid £114.