The plant light requirements calculator and the plant growth calculator are the two weather-style plant indices in the Weather & Environment category: one summarizes light, the other summarizes heat. Both are measurement worksheets rather than recommendation tools — you supply documented measurements and a named method, and the calculator returns an index you can compare against a crop-specific reference from your own source. The genuine choice is about which environmental driver you are measuring.
Neither calculator diagnoses plant condition, establishes a growth stage, or prescribes watering, nutrients, or harvest timing. Each one warns that its result is a scenario summary, not a confidence interval or a prescription.
What each calculator does
The plant light requirements calculator translates a measured PPFD and a photoperiod into daily light integral:
DLI (mol/m²/day) = PPFD × photoperiod × 3,600 / 1,000,000
The 3,600 converts hours to seconds and 1,000,000 converts micromoles to moles. The single-value method treats the entered PPFD as constant across the photoperiod. For the worked example, a PPFD of 300 µmol/m²/s over 12 hours gives 12.96 mol/m²/day; a zero PPFD or zero-hour photoperiod gives 0.00. The calculator records sensor basis, provenance, and uncertainty with the result, and it provides no lux conversion or species requirements.
The plant growth calculator accumulates growing degree days using the simple daily average:
mean temperature = (daily minimum + daily maximum) ÷ 2
daily GDD = max(0, mean temperature − base temperature)
new cumulative GDD = previous cumulative GDD + daily GDD
For the worked example, a 10 °C minimum, 24 °C maximum, and 10 °C base give 7.0 daily GDD and 7.0 cumulative GDD; a day below the base contributes zero, and the cumulative total carries forward. The method applies no upper-temperature cutoff, hourly integration, or forecast, and the base must come from a named crop or project reference.
Side-by-side comparison
| Feature | Plant Light Requirements calculator | Plant Growth calculator |
|---|---|---|
| Index computed | Daily light integral (DLI) | Growing degree days (GDD) |
| Core inputs | PPFD (µmol/m²/s), photoperiod (h/day) | Daily min/max temperature, base temperature, previous GDD |
| Formula | PPFD × photoperiod × 3,600 ÷ 1,000,000 | max(0, (min + max) ÷ 2 − base) |
| Worked example | 300 µmol/m²/s × 12 h → 12.96 mol/m²/day | 10/24 °C with 10 °C base → 7.0 GDD |
| Key boundary | Zero PPFD or photoperiod → 0.00 | Day at or below base → 0 GDD |
Verdict and limitations
Use the plant light calculator when you have light measurements and want a DLI to compare with a light target, and use the plant growth calculator when you are keeping a daily temperature log and want a running heat total for a named crop base. The two indices are complementary: light and temperature drive different parts of plant response, and each article points to the other as the natural next tool. Record the measurement basis, method version, and uncertainty with every result, and only compare against thresholds supported by the same applicable reference. A finite arithmetic result does not establish that a plant is healthy, ready to harvest, or correctly watered.