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Daily Plant Light Budget from PPFD & Duration

Calculate a daily light integral from measured photon flux and daily exposure, or find the light duration or PPFD needed for a specified photon budget.

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

An average PPFD of 200 μmol/(m²·s) for 16 hours delivers 11.52 mol/(m²·day) of photosynthetically active photons.

DLI = PPFD × illuminated hours per day × 3600 / 1000000; hours = DLI / (0.0036 × PPFD).

Worked example

Enter these known values and leave the other values blank.

Illuminated duration per day
16 hrs
Average photosynthetic photon flux density
200 μmol/(m²·s)
Daily photosynthetic light integral
11.52 mol/(m²·day)

Assumptions and limitations

  • PPFD is micromoles of photosynthetically active photons per square meter per second at the plant surface, conventionally over 400–700 nm. Use a calibrated plant-level measurement or an appropriate time average; fixture total PPF, lumens, lux and electrical watts are different quantities.
  • The formula integrates a constant PPFD, or its average over the illuminated interval, within one 24-hour day. Duration must be greater than zero and no more than 24 hours regardless of the selected time unit.
  • This retained captured operating model requires positive PPFD and positive DLI. Dark/off-state zero values are outside its domain. Enter any two known quantities and clear the third to solve its unique positive inverse.
  • For changing sunlight or dimmed lamps, integrate measured PPFD over time or use a suitable interval average. Add photon-budget contributions from different sources as DLI; do not double-count overlapping illuminated durations.
  • A fixed average month means 30.4375 days or 2629800 seconds, not a calendar month. Its selector is retained as a duration conversion; it never permits more than 24 illuminated hours in a daily calculation.
  • Equal DLI values do not make all light schedules equivalent for a plant. Crop, cultivar, growth stage, spectrum, temperature and required dark periods affect outcomes. Conditional light-budget bands provide context rather than universal crop prescriptions.

Common questions

How does PPFD become a daily light integral?

Multiply the photon flux by elapsed seconds, then divide by one million to convert micromoles to moles. Sixteen illuminated hours contain 57600 seconds.

Can the daily illuminated duration exceed 24 hours?

No. This calculator measures one daily photon budget, so a duration longer than one day is rejected in every unit.

Does the same DLI guarantee the same plant growth?

No. Spectrum, photoperiod, crop, growth stage and the environment also matter; a photon total is only one part of a growing-light plan.

References

A daily photon budget covers one 24-hour day, so illuminated duration cannot exceed 24 hours. Guard both dividing inverses with their positive denominators while preserving the captured positive operating domain and photon-count relationship.

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