How the Estimate Works
The estimator uses your LED wattage and efficacy to calculate total photon output, then distributes that output over your coverage area with an 85% capture efficiency factor — accounting for light that escapes to walls rather than hitting canopy.
Total photons (μmol/s) = Watts × Efficacy (μmol/J)Average PPFD = (Total photons × 0.85) / Coverage area (m²)This is an estimate, not a measurement. Real PPFD varies by beam angle, reflectivity of walls, and fixture height. Use a calibrated PAR meter for precise measurements.
PPFD Targets by Crop
| Crop | Min PPFD | Optimal PPFD | Sat. Point |
|---|---|---|---|
| Lettuce / Leafy Greens | 150 | 250 | 400 |
| Basil / Herbs | 200 | 300 | 500 |
| Tomato (veg) | 300 | 500 | 800 |
| Tomato (fruiting) | 500 | 700 | 1000 |
| Pepper | 350 | 600 | 900 |
| Strawberry | 250 | 450 | 700 |
| Cannabis (veg) | 300 | 600 | 900 |
| Cannabis (flower) | 600 | 900 | 1500 |
μmol/m²/s. Saturation point assumes ambient CO₂ (400 ppm). Sources: Bugbee 2017, USDA CEA data.
Estimates are useful for planning. For dialing in real results, a calibrated quantum sensor is essential — especially with LEDs, which smartphone apps and cheap meters misread by 30–50%.
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Frequently Asked Questions
What is PPFD and why does it matter?
PPFD (Photosynthetic Photon Flux Density) measures the number of photons in the 400–700nm range hitting one square meter per second, in μmol/m²/s. It is the most accurate way to describe light intensity for plants — unlike lumens or watts, which measure human perception or electrical consumption rather than plant-usable light.
How many PPFD do I need for my plants?
Seedlings and clones: 100–200 μmol/m²/s. Leafy greens (lettuce, herbs): 150–300 μmol/m²/s. Vegetative: 300–600 μmol/m²/s. Flowering / fruiting: 600–900 μmol/m²/s. High-light crops with CO₂ supplementation: 900–1500 μmol/m²/s. More is not always better — excess PPFD without CO₂ enhancement causes photoinhibition.
What is LED efficacy (μmol/J)?
Efficacy measures how efficiently a fixture converts electrical energy (watts) into photosynthetically useful photons (μmol). Modern quality LEDs achieve 2.8–3.2 μmol/J. Budget blurple fixtures typically reach 1.5–2.0 μmol/J. Top commercial fixtures (Fluence, Gavita) reach 3.5 μmol/J. Higher efficacy means more light per watt — lower electricity cost per gram of yield.
Is PPFD the same across the whole canopy?
No. PPFD is highest directly below the light and falls toward the edges. Our estimator calculates average PPFD over the coverage area and estimates peak center PPFD at approximately 1.3× the average — a typical ratio for modern LED panels at recommended hanging heights. For a precise map, use a PAR meter at multiple points.
What PAR meter should I use to measure PPFD?
The Apogee MQ-500 (full-spectrum quantum sensor) is the gold standard for LED measurement — LEDs emit light at wavelengths that cheap lux-based meters misread significantly. The Apogee SQ-520 is a good budget alternative. Avoid using smartphone apps — they are calibrated for human vision, not plant-usable light, and can be off by 30–50% under LEDs.