- Select whether you are targeting PPFD or DLI.
- Enter area, photoperiod, and existing canopy PPFD.
- Provide target PPFD, or target DLI for conversion.
- Set efficiency and uniformity to match your layout.
- Enter fixture PPF, or estimate it using efficacy.
- Press Calculate. Results appear above the form.
- Download CSV or PDF for notes and planning records.
| Scenario | Area | Existing PPFD | Target | Photoperiod | Efficiency | Fixture | Output |
|---|---|---|---|---|---|---|---|
| Seedlings | 2.4 m² | 120 | 250 PPFD | 16 hr | 75% | 480 µmol/s | Fixtures sized by tool |
| Leafy greens | 3.0 m² | 180 | 14 DLI | 14 hr | 70% | 2.7 µmol/J @ 240 W | PPF estimated by tool |
| Overwintering | 25 ft² | 90 | 220 PPFD | 12 hr | 65% | 350 µmol/s | Cost and DLI reported |
Lighting goals for indoor gardening
Supplemental lighting fills the gap between available daylight and the intensity plants need for steady growth. This calculator estimates how many fixtures are required to reach a chosen PPFD or DLI target over a defined photoperiod, supporting consistent results across seasons. It is useful for shelves, grow tents, propagation benches, and small greenhouses where winter light is limiting.
Key inputs that change the fixture count
Area, existing PPFD, and target level set the supplemental PPFD requirement. Efficiency represents canopy utilization, fixture optics, height losses, and maintenance conditions, while the uniformity factor covers edge falloff and spacing. Together, these inputs convert a canopy target into total photon flux needed. When plants are trained, moved, or staged, recheck area and uniformity to avoid underlit corners.
Fixture specifications and verification steps
You can enter fixture PPF directly from a datasheet, or estimate it from efficacy and watts when only electrical data is available. After installation, verify PPFD at canopy height at multiple points, then update efficiency or uniformity to match real distribution. Keep sensors level, measure at the same time of day, and record mounting height for repeatable checks.
Interpreting DLI, energy, and cost outputs
The results include existing, supplemental, and total DLI values computed from PPFD and hours per day. Energy use scales with fixture watts and photoperiod, producing daily and monthly kWh. Cost estimates apply your utility rate and selected currency for quick budgeting. Use monthly totals to compare schedules, such as longer hours at lower intensity versus shorter high-intensity runs.
Practical planning and optimization guidance
Use the output to compare fewer high-PPF fixtures versus more smaller units, and to test longer photoperiods versus higher intensity. If the calculated fixture count feels high, improve efficiency through better height, layout, and reflective surfaces before increasing power. Also consider dimming controls and timers to fine-tune DLI as daylight changes. For seedlings, gradual ramping helps prevent stress and lets you confirm targets early with leaf color and internode spacing.
What is the difference between PPFD and DLI?
PPFD is instantaneous light intensity at the canopy. DLI is the total photons delivered over a day. This calculator converts between them using your photoperiod to keep targets consistent across seasons.
How do I measure existing PPFD accurately?
Use a PAR meter at canopy height. Take several readings across the area and average them. Measure with the same fixture height and typical daylight conditions you expect during the schedule.
What efficiency value should I start with?
For simple setups, 70–80% is a practical starting range. Lower it if lights are high, spacing is wide, or surfaces absorb light. Increase only after measurements confirm better utilization.
Why is there a uniformity factor?
Uniformity accounts for edge losses and spacing variation so the whole canopy meets the target, not only the center. Use higher values for strict uniformity needs or irregular layouts.
When should I use efficacy mode instead of PPF?
Use efficacy mode when you know fixture watts and published efficacy but do not have a PPF rating. The calculator estimates PPF as efficacy multiplied by watts, then sizes fixtures accordingly.
How can I reduce energy cost without hurting growth?
Try extending photoperiod slightly, improving reflectivity, lowering mounting height safely, or using dimming. Recalculate DLI and cost for each change, then verify plant response with measurements.