Daily Light Integral (DLI) Calculator
Daily photon budget, crop goals & photoperiod planning.
Editable goal examples — verify species, cultivar and growth stage.
Light & Photoperiod Inputs
Daily Light & Goal Summary
Example calculation500 μmol/m²/s × 12 hours
Photoperiod & Light Visualizer
Photosynthetically Active Radiation (PAR) Reference
Crop stage, spectrum and the light/dark cycle matter. Lux conversion depends on the source spectrum.
Model Checks
- 1Measure average light at the canopy
- 2Set a verified crop-specific goal
- 3Check intensity and day/night duration
Formula & Worked Example
Frequently Asked Questions
Can lux be converted directly to PPFD?
Only approximately with a light-source-specific factor. Lux and foot-candles weight light for human vision, while PPFD counts PAR photons. The Sunlight and HPS options use Purdue HO-238 Table 1 factors; a custom LED needs a measured or manufacturer-provided calibration. A quantum sensor is preferred.
Does equal DLI mean equal crop growth?
No. Spectrum, intensity, photoperiod, temperature, CO₂, cultivar and growth stage can change plant response even at the same DLI. The goal-progress bar measures only the fraction of your entered photon target; it is not an optimum or safety assessment.
What if the target needs more than 24 hours?
The target is not attainable in a single 24-hour day at that PPFD. Find Hours shows the mathematical requirement and an infeasibility notice. The clock is cleared instead of drawing a false schedule. Increase intensity or revise the independently verified target.
Are crop presets universal recommendations?
No. The 12, 20, 30 and 22 mol examples are editable planning goals, not cultivar-specific recommendations. Selecting one changes the goal only; verify the species, cultivar, growth stage and lighting regime from an appropriate crop guide.
More calculation questions
What is Daily Light Integral?
DLI is the total PAR photon quantity received per square meter over one day, expressed as mol/m²/day. It integrates photon flux over time rather than measuring wavelength, electricity consumption or human-visible brightness.
What formula is used?
For constant or representative light-on average PPFD, DLI = PPFD × hours × 3600 / 1000000 = PPFD × hours × 0.0036. Required PPFD = target DLI / (hours × 0.0036); required hours = target DLI / (PPFD × 0.0036).
Which average PPFD should I enter?
Enter a representative canopy-level average during the entered light-on hours. A single changing-sunlight reading cannot represent a whole day. A 24-hour mean that includes darkness should instead be multiplied by 24 hours; do not multiply that mean by light-on hours again.
How do foot-candles and lux relate?
One foot-candle equals 10.76391041671 lux. Purdue lists approximate PPFD = fc × 0.20 for sunlight and fc × 0.13 for HPS. These become approximately 18.58 and 12.08 μmol/m²/s per klux. Neither is a universal LED factor.
Can the clock represent light across midnight?
Yes. The entered start time plus the photoperiod wraps through midnight. It is an illustrative light-on schedule, not a sunrise forecast. A 24-hour photoperiod has no dark interval; a zero-hour photoperiod is all dark. Crop suitability must be assessed separately.
What happens with zero PPFD or zero hours?
Forward DLI is zero. A positive target cannot be reached by solving for PPFD at zero hours or for hours at zero PPFD. The tool shows no finite result rather than dividing by zero. Goal DLI must be positive to calculate progress.
Is the PAR strip a measured light spectrum?
No. The 400–700 nm strip is a reference band. PPFD, lux and DLI alone do not describe spectral distribution, fixture efficiency, spatial uniformity or the fixture’s measured spectrum.
Do the controls update immediately?
Yes. Modes, goals, intensity, duration, source factor and schedule update together. PPFD/lux/fc switches preserve physical PPFD when a valid source conversion exists. Changing the source while entering lux/fc reinterprets the same reading with the selected factor. Copy includes the model assumptions.
Sources & References
Purdue ExtensionMeasuring Daily Light Integral · HO-238
Reference information is not institutional endorsement.
Calculate daily PAR photon dose from average canopy PPFD and photoperiod, or find required PPFD or hours for an editable DLI goal.