I don’t see where it says how much electricity the light actually uses:
300W LED Panel Grow Light Veg Lamp
LED Output Power:300W
LED Quantity:100PCS x 3W LEDs
Frequency: 50/60 HZ
Maybe I’m blind… assuming it’s somewhere around 150w you should be able to flower a 3-4 square feet of space. The tent itself is 6.25 square feet. If you were to fill the entire tent with plant, you’d want two of those lights (assuming 150w of actual electrical consumption is accurate).
They call that a “300W” light because it has 100 three watt diodes on it… but they aren’t driving (powering) them to their max wattage, so it’s not really a 300W light.