Compute the required photon flux: PPFD × grow area — both in the units the canopy actually receives and the area it covers.

Split that flux across one de-rated fixture: N = PPFD × A ÷ (efficiency × wattage × maintenance × thermal × dimming), rounded up to whole fixtures.

Charge the photoperiod: kWh/day = N × watts × hours ÷ 1000 × (1 + ballast/100) — the ballast overhead sits on top, invisible at the bulb.

Price it: cost per day = kWh × rate, then cost per month (×30) and cost per 90-day cycle fold the recurring line into the production budget.

Verify the optics: delivered PAR = N × w × e × m × τ × δ ÷ A against the target, plus the effective µmol/J after the three derates.

Run the comparison and the band: LED cost at your efficiency vs HPS at 1.7 µmol/J, then green/yellow/red on e_eff with the $50/day bill red flag.