Watts tell you about power use, and lumens are tuned to human vision. PPFD is measured at the canopy, so it shows what the plants get. Rough targets without CO2: 100-300 for seedlings, 300-600 in veg, 600-1000 in flower.
It varies across the tent: the middle is strong, the edges weaker. A lamp with a PPFD map at a given height lets you plan the hanging height and see how even the light is. Compare lamps in full-spectrum LEDs, and check efficiency (µmol/J) as well.
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