育成ライトの定格PPFDまたはluxから、逆二乗の法則を使ってキャノピー（葉冠）位置での光量を計算。生育ステージ別の推奨値付き。
| Distance | PPFD (µmol/m²/s) | Approx lux |
|---|
Light intensity falls off with the inverse square of distance: I₂ = I₁ × (d₁ / d₂)². Doubling distance cuts intensity to a quarter.
PPFD → lux: for white LEDs roughly 1 PPFD ≈ 54 lux. For HPS ≈ 82 lux. Plants care about PPFD (photosynthetically active 400–700 nm), not lux — but lux meters are cheaper.
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