Horticultural Fixture Count and Energy
Counts fixtures from target PPFD, fixture PPF, and the on-target fraction, then reports connected load, efficacy.
Example
You enter
- Growing area (sq ft) 1000
- Target supplemental PPFD (micromol/m^2/s) 200
- Fixture PPF (micromol/s) 1700
- Fixture input power (W) 645
- On-target fraction 0.9
- Photoperiod (hours) 16
- Season length (days) 180
- Energy rate ($/kWh) 0.12
You get
- Growing area (m²) 92.903
- Photons required 18,581 micromol/s over 92.9 m^2
- Exact count 12.1442
- Fixtures required 13 (exactly 12.14)
- Perfect count 11
- Connected load 8,385 W, 90.3 W/m^2
- Watts per m² 90.2554
- Fixture efficacy 2.64 micromol per joule
- Seasonal energy 24,149 kWh, $2,898
- Season cost 2897.86
- Heat added to the house 28609.6
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method.
Details, formula, and sources
ScopeSeasonal energy, and the heat added to the house. Every connected watt arrives as heat: a credit in December, a cooling load in March, which makes lighting and ventilation one decision.
Formula or tablephotons required = target PPFD x area in square metres; fixtures = required / (fixture PPF x on-target fraction), rounded up; efficacy = PPF / input watts; heat = connected watts x 3.412 Btu/h.
Source and editionThe fixture manufacturer's PPF rating and a photometric layout govern the actual distribution.
Free accessPublic arithmetic; PPF ratings are published by fixture manufacturers.
What governsEstimate. AHJ and licensed professional govern.
API field namesgrowing_area_sqft, target_ppfd_umol_m2_s, fixture_ppf_umol_s, fixture_watts, on_target_fraction, photoperiod_hours, season_days, energy_rate_per_kwh, growing_area_m2, photons_required_umol_s, exact_count, fixture_count, perfect_count, connected_load_w, watts_per_m2, efficacy_umol_per_joule, season_kwh, season_cost, heat_btuh
- On-target fraction entered; the share of emitted photons landing on the crop rather than the aisle or wallphotometric layout
- Distribution uniform average assumed; a real layout has a distribution the count does not capturemanufacturer photometrics