How high to hang your LED at each stage, which PPFD and DLI values to aim for, how to use the dimmer and how to measure light with a PAR meter, lux meter or app.
How many hours of light each stage needs, how to switch to 12/12, why darkness must be total during flowering and which timer or controller to choose.
How many real watts each grow tent needs, how to read PPF and efficiency on the spec sheet and when HPS still makes sense, with a worked electricity cost calculation.