Estimate daily plant light from intensity and time
A Daily Light Integral calculator estimates total usable light plants receive in 1 day. DLI is usually reported as moles of photons per square meter per day, written as mol/m2/day.
Calculate DLI by multiplying PPFD by light hours by 3,600, then dividing by 1,000,000. PPFD is the average light intensity at canopy level in micromoles per square meter per second.
For example, 500 umol/m2/s for 16 hours equals 28.8 mol/m2/day.
Use target DLI, natural light, area, fixture wattage, and electricity price to plan indoor grow lights, greenhouse supplemental lighting, seed starting, houseplants, microgreens, and flowering crops.
Total Daily Light Integral
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Fixture DLI
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Target status
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Required PPFD
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Required light hours
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Supplemental DLI needed
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Monthly electricity cost
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PPFD used
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Natural light
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kWh per day
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Canopy area
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DLI breakdown
Shows light intensity, photoperiod, target gap, required settings, and electricity math.
| Item | Estimate | Formula | Note |
|---|---|---|---|
| Run the calculator to see the DLI breakdown. | |||
Grow note: Measure PPFD at canopy level in multiple spots when possible. DLI can vary across a tray, bench, tent, or greenhouse bay because of fixture spacing, plant height, reflectors, sun angle, and shading.
How to use the Daily Light Integral calculator
- Choose a light input: Use measured PPFD if you have a PAR meter, lux estimate for rough comparisons, or fixture PPF and area for a layout estimate.
- Enter light hours: Use the number of hours the crop receives that average intensity each day.
- Add target DLI: Use a goal that matches the crop, growth stage, and production style.
- Add natural light: For greenhouse or window growing, enter sunlight DLI so the calculator can estimate supplemental light needs.
- Include uniformity loss: Reduce the estimate if light is uneven or the canopy edges are much dimmer than the center.
- Add electricity inputs: Fixture watts and electricity rate estimate daily and monthly operating cost.
Daily Light Integral formula
DLI converts light intensity and time into the total daily quantity of usable plant light. It is a useful bridge between instant PPFD readings and full-day crop light targets.
DLI = PPFD x hours x 3,600 / 1,000,000
Required PPFD = target DLI / hours / 0.0036
Required hours = target DLI / PPFD / 0.0036
Example: 300 umol/m2/s for 16 hours gives 17.3 mol/m2/day because 300 x 16 x 0.0036 = 17.28.
Formula and units reference: Virginia Cooperative Extension - Calculating and Using Daily Light Integral.
Quick PPFD to DLI reference
Use this table to sanity-check a light plan before fine-tuning the calculator. Each value assumes steady average PPFD at canopy level for the full photoperiod.
| Average PPFD | 12 hours | 14 hours | 16 hours | 18 hours | Best fit |
|---|---|---|---|---|---|
| 100 umol/m2/s | 4.3 | 5.0 | 5.8 | 6.5 | Low-light plants, gentle propagation, shaded spaces. |
| 200 umol/m2/s | 8.6 | 10.1 | 11.5 | 13.0 | Seedlings, cuttings, microgreens, compact starts. |
| 300 umol/m2/s | 13.0 | 15.1 | 17.3 | 19.4 | Lettuce, leafy greens, many herbs. |
| 500 umol/m2/s | 21.6 | 25.2 | 28.8 | 32.4 | High-light herbs, fruiting crops, flowering crops. |
| 700 umol/m2/s | 30.2 | 35.3 | 40.3 | 45.4 | Intensive production where climate and CO2 can keep up. |
Common DLI target ranges
Crop targets vary by cultivar, growth stage, temperature, CO2, and nutrition. Use these broad ranges for planning, then refine with crop response and local guidance.
| Crop type | Typical planning range | Use note |
|---|---|---|
| Low-light houseplants | 2 to 6 mol/m2/day | Useful for shade-tolerant plants and low-intensity indoor spaces. |
| Seedlings and propagation | 6 to 12 mol/m2/day | Young plants often need moderate light without excessive stress. |
| Leafy greens and herbs | 12 to 20 mol/m2/day | Common range for lettuce, basil, greens, and many indoor production crops. |
| Fruiting and flowering crops | 20 to 35+ mol/m2/day | Higher targets may require stronger fixtures, longer days, or supplemental CO2 and climate control. |
How to adjust DLI safely
Raise intensity
Move fixtures closer or increase dimmer output, but watch for heat, bleaching, leaf curl, or edge stress.
Extend photoperiod
Longer days can raise DLI without raising peak PPFD, but some crops respond to day length and need dark periods.
Improve uniformity
Adjust fixture spacing, reflective walls, bench placement, or canopy height so edges do not lag behind the center.
How to measure PPFD for a better DLI estimate
The calculator is most accurate when the PPFD input represents the whole canopy, not one bright measurement. Use a simple measurement grid to capture light intensity where plants actually receive it.
| Step | How to do it | Why it matters |
|---|---|---|
| Measure at canopy height | Place the sensor where the top leaves receive light. | PPFD changes quickly with fixture distance and plant height. |
| Use several points | Measure center, corners, edges, and any visibly dim zones. | Average PPFD gives a better DLI estimate than a single hotspot. |
| Check full output | Record dimmer setting, fixture height, and spectrum setting when measuring. | Small changes can make old readings inaccurate. |
| Repeat after canopy growth | Recheck after pruning, transplanting, trellising, or a major height change. | The canopy can move closer to the light or shade itself over time. |
Supplemental lighting in greenhouses and windows
Natural light can cover part of the daily target, but it changes with season, latitude, clouds, glazing, shade, and time of day. Use the natural DLI field to avoid overestimating how much grow-light time is needed.
Winter production
Short days and weak sun usually increase supplemental DLI needs, especially for seedlings, greens, flowers, and fruiting crops.
Cloudy periods
A cloudy week can push plants below target even if the average month looks adequate, so daily tracking can be useful.
Shade and glazing
Screens, dirty glazing, neighboring buildings, and window angle can reduce natural DLI before light reaches the canopy.
Greenhouse DLI planning reference: Michigan State University Extension - Daily Light Integral Maps.
Interesting Fact
A greenhouse can look very bright while still delivering much less plant light than an outdoor growing area. Virginia Cooperative Extension notes that greenhouses typically receive 30% to 50% less light than open fields because glazing and structural components reduce transmission. That means an outdoor DLI of 20 mol/m2/day might become only about 10 to 14 mol/m2/day inside before other shade losses are considered. Source: Virginia Cooperative Extension - Calculating and Using Daily Light Integral.
Troubleshooting DLI results
A good DLI number does not guarantee a good crop by itself. Use this table when plants look off even though the calculator says the target is close.
| Pattern | Possible cause | What to check next |
|---|---|---|
| Stretchy growth | DLI may be too low, or spectrum and spacing may be poor. | Measure edge PPFD, increase uniformity, or extend photoperiod. |
| Bleached or curled leaves | Peak PPFD may be too high even if daily DLI is acceptable. | Raise lights, dim fixtures, or spread light over a longer photoperiod. |
| Good center, weak edges | Light distribution is uneven across the canopy. | Adjust fixture spacing, side reflection, or enter a uniformity loss. |
| Slow growth despite target DLI | Temperature, nutrition, irrigation, CO2, or root health may be limiting. | Check the growing environment before adding more light. |
Indoor plant light reference: University of Maryland Extension - Lighting for Indoor Plants.
Frequently Asked Questions
What does daily light integral mean for plants?
Daily light integral, or DLI, is the total amount of photosynthetically active photons plants receive over one day. It is usually expressed as mol per square meter per day, so it connects light exposure, photosynthesis, and time in one number. Growers use DLI to compare sunlight, greenhouse conditions, indoor fixtures, and crop light targets.
How do I use PPFD to calculate daily light integral?
Multiply average PPFD by light hours and then by 0.0036. For example, 250 umol/m2/s for 14 hours gives 12.6 mol/m2/day. Use an average canopy-level PPFD across the growing area, not a single bright spot directly under the fixture, because DLI is based on photons reaching each square meter over the full day.
Can this calculator estimate DLI from lux or PAR readings?
You can estimate daily light integral from lux, but it is less accurate than using a PAR meter or PPFD sensor because lux is weighted for human vision, not plant photosynthesis. The conversion factor depends on the grow light spectrum and can vary between LEDs, sunlight, fluorescent lamps, and other sources. Use lux mode for rough comparisons, then use measured PPFD when crop decisions matter.
Should I increase PPFD or light exposure hours to reach target DLI?
Both approaches can raise DLI. Increasing PPFD raises intensity and may increase heat or light stress, while extending the daily exposure spreads photons over more hours. The best choice depends on crop type, growth stage, day-length sensitivity, grow light capacity, electricity cost, and temperature control.
What DLI target should I use for seedlings, vegetables, cannabis, or other crops?
Start with the crop preset closest to your growing goal, then adjust from plant response and crop-specific guidance. Seedlings and cuttings often need a lower DLI than leafy vegetables, while basil, tomatoes, cucumbers, regulated cannabis crops, and flowering crops usually need more daily light. The right target also depends on growth stage, temperature, CO2, nutrition, cultivar, and whether you are growing for compactness, flavor, yield, or flowering.
Why should I use average canopy PPFD instead of grow light wattage?
Grow light wattage tells you electrical power use, not how many useful photons reach the leaves. Average canopy PPFD captures fixture output, hanging height, beam angle, canopy area, dimmer setting, reflectors, and edge losses. For the best daily light integral estimate, measure several spots across the canopy and average them instead of using one reading from the brightest point.
How do I combine sunlight and grow light output in one DLI estimate?
Enter measured or estimated sunlight in the natural DLI field, then enter the PPFD and hours from your grow light. The calculator adds natural DLI and fixture DLI, then shows how much supplemental light is still needed to reach the target. This is especially useful for a greenhouse, windowsill, sunroom, or vegetable production setup where sunlight changes by month, cloud cover, and weather.
Can daily light integral be too high for plants?
Yes. Too much daily light integral or too much peak PPFD can cause bleaching, curled leaves, tip burn, water stress, or growth that outpaces nutrition and climate control. Some crops also need a dark period or respond strongly to photoperiod, so running lights longer is not always the best solution. Increase light exposure gradually and watch leaf temperature, irrigation demand, airflow, and plant response.
Other useful calculators
Disclaimer: This Daily Light Integral calculator is for general horticulture, greenhouse, indoor gardening, and educational planning only. It provides approximate DLI, required PPFD, required light hours, supplemental light needs, and electricity cost from user-entered PPFD, lux, fixture PPF, canopy area, photoperiod, natural light, target DLI, uniformity loss, fixture watts, electricity rate, and days per month.
Actual plant response can vary because of species, cultivar, growth stage, temperature, humidity, CO2, nutrition, irrigation, root-zone conditions, leaf temperature, fixture spectrum, canopy shape, sensor accuracy, fixture height, reflective surfaces, shading, photoperiod sensitivity, and stress history. Lux conversions and fixture PPF estimates are approximations and should not replace measured canopy PPFD when precision matters.
Use crop-specific production guidance, light manufacturer data, PAR meter readings, greenhouse records, and professional horticulture judgment for commercial decisions. This calculator is not a guarantee of growth, yield, flowering, crop quality, energy savings, or plant health.
Last updated: June 1, 2026