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Cost-per-DLI Calculator.

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Cost-per-DLI Calculator

What does it cost to deliver one mol of light dose to one square meter? The economic-decision metric for fixture selection.

Per-fixture economics

Typical modern LED 2.5–3.0; older HID 1.4–1.7
Fraction of lighting energy spent on cooling it
For amortized cost over lifetime
Fixture PPF —μmol/s Power × PPE
Average canopy PPFD —μmol/m²/s Across coverage area
Daily DLI delivered —mol/m²/d vs target
Daily energy cost (light only) $— Per fixture per day
Daily energy cost (light + HVAC) $— Total daily operating cost
Cost per mol delivered $— $/mol photons
Cost-per-mol per m² $— Headline efficiency metric
Annual energy cost $— Continuous operation

Why this metric matters

Fixtures are sold on PPE (μmol/J) and price. But the real cost-of-operation depends on:

  • Power draw × hours × electricity rate
  • HVAC load to remove the heat the fixture produces
  • Cooling efficiency of the HVAC (EER)
  • How efficiently the fixture's photons reach the canopy

Cost-per-mol-per-m² rolls all of these into a single decision-grade number. A high-PPE fixture with high purchase price but lower energy bills may have lower cost-per-mol than a cheap fixture with worse PPE.

Reference benchmarks

Setup$/mol/m²Notes
Modern LED, PPE 2.85, $0.10/kWh, EER 14~$0.040Best-case indoor
Modern LED, PPE 2.85, $0.13/kWh, EER 11~$0.055Typical indoor
Older LED, PPE 2.2, $0.13/kWh, EER 11~$0.075Common older indoor
HPS DE 1000W, PPE 1.7, $0.13/kWh, EER 11~$0.090HID with HVAC
HPS, $0.30/kWh CA peak, EER 10~$0.230Worst case high-rate
Greenhouse with no HVAC, supplemental LED~$0.018Best when sun does most work

For a 50 mol/m²/day cannabis flower run over 65 days: at $0.05/mol/m², ~$162 per square meter per cycle just in lighting energy. At $0.09/mol/m² (HID): $292 — almost double. Per pound harvested, this is the difference between a viable margin and a losing operation.

Hidden costs to remember

  • Fixture amortization — typical lifetime 50-90,000 hours. A $1200 fixture amortized over 50,000 hours = $0.024/hour. Add to operating cost.
  • Driver replacement — LED drivers fail more than LEDs. Plan for some maintenance.
  • Heat removal infrastructure — bigger HVAC = bigger upfront cost and higher demand-charge exposure for commercial accounts.
  • Demand charges — commercial electric rates often have a peak-demand component. Lighting startup spike matters.
  • Insurance / labor — heat-related, equipment-related, etc. Not in this calculator but real.

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