as some others and i tried to explain you in an other thread, watt you'll need will depend on the area you'll want to flower due to how light dispersion quiclky decrease with artificial light (unlike the sun) when not directly under the source and getting far from it and this independtly from light schedule (as you're supposed to stay within a certain range anyway 12/12 to 20/4).
LED brand scale their LED panel wattage so you can achieve a certain DLI for a certain area when you're in that light schedule range.
Daily Light Integral represent the optimum amount of light a plant can sustain per day. It's a relation between the ppfd values of your light across the area/canopy and the time it's exposed to light.
What is DLI and how can it help you to grow bigger, better cannabis plants without spending a dime? It sounds too good to be true, but it's not!
www.growweedeasy.com