Why wattage is the wrong unit
Wattage tells you what the fixture draws, not what reaches the canopy. Plan by PPFD at canopy height and total daily light integral.
Stage targets
Seedlings need gentle light, veg wants steady intensity to build structure, and flower can take significantly more if temperature and CO2 keep up.
Reading the plant
Tacoing leaf edges and bleached top colas mean too much intensity long before a meter tells you.