How Grow Light Check estimates plant-level light

Evidence priority

1. PPFD measured at a known distance
2. Published photosynthetic photon flux (PPF)
3. Photon efficacy (PPE) multiplied by actual electrical watts
4. Center beam candlepower for a directional reflector
5. Lumens converted conservatively for an ordinary broad-white LED

Watts alone are treated as insufficient because they describe power consumption, not photon output or distribution.

Geometry and daily light

Directional lamps use a cosine-power beam derived from the published beam angle. Panels and bars are divided into emitting regions so their size affects near-field distribution. The model calculates PPFD at the leaves and daily light integral as DLI = PPFD × hours × 0.0036 for constant electric lighting.

Transparent covers, mesh and water can reduce output. When selected, bounded transmission estimates are applied after the open-air light calculation.

How a recommendation is chosen

The engine compares simulated PPFD and DLI with practical plant target bands. Uncertainty trials reflect weaker source data and missing specifications. A recommended distance requires most trials to fit; an uncertain fit is labeled accordingly rather than presented as exact.

Known limitations

• CCT does not provide a complete spectral power distribution.
• A beam angle cannot reproduce reflector rings, asymmetric output or every diffuser loss.
• A single center PPFD value does not describe the canopy average.
• Walls and tent reflections are excluded when geometry and reflectance are unknown.
• Watering, temperature, nutrition and species response still affect growth.

For valuable or sensitive setups, confirm the final position with a cosine-corrected PAR or quantum meter.

Core references

• Illuminating Engineering Society: beam angle
• Peer-reviewed guidance on photometric and photosynthetic quantities
• University of Maryland Extension: lighting indoor plants
• Virginia Cooperative Extension: daily light integral

Review and maintenance

Plant targets, supported evidence paths, and recommendation records are versioned in the project source and protected by automated tests. Product recommendations are reviewed separately from calculator results, and affiliate availability cannot change the suitability calculation. Report a reproducible issue or stronger source to nopredevelopment@gmail.com.

See the separate product recommendation method for identity, evidence-tier, safety, and affiliate rules.