For stable electric lighting, DLI = PPFD × hours × 0.0036. For changing output, DLI is the time integral of repeated PPFD measurements; the schedule tool approximates that integration with stable blocks.
Light reading
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PPFD is intensity now. DLI is exposure over time.A calibrated quantum sensor gives the strongest direct measurement context.
Daily light exposure
12 hours light in a 24-hour day
30.2Calculated DLI
—PPFD for your target DLI
—Stage context
—Measurement context
Why it changesAt the same PPFD, a longer photoperiod increases DLI. This shortcut assumes PPFD is stable while the lights are on; variable sunlight or dimming schedules require integrated measurements over time.
Variable-light DLI schedule
Use this when PPFD changes during the light period. Add each stable time block; the tool integrates photon exposure across the schedule instead of pretending one reading represents the whole day.
0.0 mol·m⁻²·day⁻¹
0.0 scheduled hours
DLI = Σ(PPFD × hours × 0.0036) for each block.
Use blocks only when output is reasonably stable inside each block.For sunlight, cloud-driven changes, or frequent dimming, use a logger that records PPFD repeatedly and integrate the time series.
Light logger
Track intensity over time.
Log repeated readings to inspect warmup, drift, daylight changes, dimming behavior and other time-dependent light patterns instead of relying on one snapshot.
0readings
0mlogged duration
—average
—median
—min / max
—logged photon integral
| Time | Basis | Reading | Method | Note |
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Measurement boundary: PPFD and ePAR are not interchangeable labels. Select ePAR only when the instrument or app actually measures the extended 400–750 nm range. The logged photon integral is calculated only across the recorded timestamps; it is not automatically a full-day DLI.
No readings logged yet. Auto-log records the value currently displayed on this page and stops if this page is closed.
Fixture calibration
Map the dimmer to measured light.
Grow-light output is often non-linear. Save measured output points for a fixture, then estimate PPFD and DLI between those points instead of assuming 50% dimmer means 50% photons.
One point per line as dimmer%:PPFD. Use at least two points. Values between measurements are interpolated; values outside the measured range are not extrapolated.
—Estimated PPFD
—Estimated DLI at current photoperiod
—Measured dimmer range
—Calibration age
Calibration profiles stay in this browser unless included in an exported survey.
Calibration is setup-specific.Changing fixture model, fixture count, mounting height, optics, diffuser, canopy plane, sensor, or major room geometry can invalidate the response curve. Re-check after material changes.
Survey record
Preserve the conditions behind the map.
A PPFD map is only comparable when fixture, sensor, height, power and canopy-plane context are recorded with it.
Survey data stays in this browser unless you export it.
Repeatability record
For comparisons, keep fixture model/count, dimmer setting, fixture-to-canopy height, sensor mode, sensor identity, canopy plane, and measurement geometry consistent. Record the most recent calibration or verification date when known.
Save at least two surveys to compare average PPFD, uniformity and variability.
Canopy mapper
One center reading is not a canopy.
Enter a grid of readings to expose hotspots, weak corners and uneven coverage. The map keeps every numeric value visible so color is never the only information.
Map setup
Measure at the same canopy plane. Keep fixture height, power and room conditions consistent while mapping.
PPFD heatmap
On small screens, this measurement grid can be scrolled horizontally.
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Delta view: green = ≥25 PPFD higher than baseline, red = ≥25 lower, gold = within ±24, gray = missing paired reading.
—Average PPFD
—Median PPFD
—Minimum
—Maximum
—Min ÷ average (legacy)
—Coefficient of variation
—Within ±10% of average
—Within ±20% of average
—Perimeter ÷ center average
—Approx. point spacing
—Inside your target range
—DLI range across map
—Max ÷ min spread
—Points mapped
Repeatable mapping protocolWarm the fixture, lock dimming and mounting height, measure on one canopy plane with the sensor level and unobstructed, include edges/corners, and repeat the same grid after any lighting change.
How to read uniformity
Min ÷ average is kept because growers and fixture maps commonly use it, but it can be distorted by one unusually low point. Also review coefficient of variation, the share of readings within ±10% and ±20% of the average, and perimeter-vs-center exposure.
Teaching Healthy Cultivation
Learn while you measure.
The tool explains what each number can tell you—and what it cannot prove by itself.
PPFD vs PAR
PAR describes the photosynthetically active waveband conventionally measured from 400–700 nm. PPFD describes how many photons in that band arrive at a square meter each second.
PPFD vs DLI
PPFD is instantaneous photon flux density. DLI integrates photon exposure across time. Converting one spot PPFD reading to DLI is valid only when output is reasonably constant during the stated photoperiod; variable daylight or scheduled dimming should be logged and integrated.
PAR vs ePAR
Conventional PPFD counts photons from 400–700 nm. ePAR/ePPFD extends the measurement range to approximately 400–750 nm. Preserve the sensor mode with every record because the two values are not interchangeable.
Same PPFD ≠ same spectrum
Two fixtures can produce the same PPFD while distributing photons differently across blue, green, red and far-red wavelengths. PPFD does not describe spectral composition.
Canopy interception
A top-canopy reading does not describe every leaf. Leaf angle, density, training, spacing and self-shading alter how radiation is intercepted deeper in the canopy.
Measurement quality
Real sensor measurements are strongest when the sensor is level, representative of canopy height and appropriate for the source spectrum. Manufacturer maps and estimates are reference context, not measurements of your room.
Acclimation matters
Plant response depends on the previous light environment. Large intensity changes can alter leaf energy balance, transpiration and water demand even when the final intensity is reasonable.
Measurement protocol
Keep the sensor plane consistentMeasure at the same crop plane and keep the sensor level. Cosine-corrected sensors are designed to account for light arriving from different angles, but poor positioning still changes what you are measuring.
Record sensor modePPFD/PAR conventionally covers 400–700 nm; ePPFD/ePAR extends the measured range. Do not compare the two as if they were identical.
Map the whole canopyCenter-only readings can hide weak edges or hotspots. Repeat the same grid after fixture height, dimmer, canopy height, or geometry changes.
Do not infer spectrum from PPFDEqual PPFD can come from very different spectral distributions. Record fixture/spectrum context separately when it matters.
Evidence-aware education
What the research actually supports
One controlled 2022 study tested average canopy PPFD of 600, 800 and 1,000 µmol·m⁻²·s⁻¹ for 12 h in one cultivar. A 2025 greenhouse study tested 150–700 µmol·m⁻²·s⁻¹ of supplemental LED plus sunlight across static and dynamic programs. These are treatment conditions from specific experiments—not universal target bands.
DLI and photoperiod are related but not interchangeable. Cannabis flowering behavior can respond to daylength independently of the total photon dose, and cultivar differences matter.
Quantum sensors are designed with cosine response so photons arriving at oblique angles are weighted appropriately. Keep the sensor plane consistent and record the measurement geometry; a map is only comparable when the setup is repeatable.
Spatial-light research in controlled environments has shown that minimum-to-average PPFD can overemphasize a single weak point. Distribution-based measures and normalized point values give a fuller picture of canopy uniformity, so this map reports CV plus the share of readings close to the mean and compares perimeter to center.
Connected measurement
Authenticated light provider.
Read normalized PPFD from the same-origin telemetry gateway when a compatible provider/device is configured. Provider credentials remain server-side.
—provider
0mapped metrics
—latest observation
No authenticated provider loaded. Provider polling updates the current reading only; it never auto-logs or changes PAR/ePAR basis.