What is Daily Light Integral (DLI)?
Daily Light Integral (DLI) is the total amount of photosynthetically active radiation (PAR) delivered to a plant over a full 24-hour day, measured in moles of light per square meter per day (mol/m²/day). It is the single most useful number for comparing how much light different growing setups actually deliver, because it folds together both light intensity and how long the light is on. [2, 1, 3]
The formula
How the chart works
On the calculator's chart, photoperiod runs along the x-axis and PPFD up the y-axis. Because DLI is the product of the two, every point that shares the same DLI traces a curve of the form PPFD = DLI ÷ (hours × 0.0036) — a hyperbola. These constant-DLI "iso-curves" divide the grid into shaded zones, each colored by DLI level from low to very high. Your current intensity and duration are plotted as a live marker, so you can see at a glance which zone you're in and how to move between them: more hours or more intensity both push you toward higher DLI.
The low / moderate / high / very-high labels follow Purdue Extension's categories for greenhouse crops: low-light crops need 3–6 mol/m²/day, medium 6–12, high 12–18, and very high more than 18. [1] The optional heatmap view shows the same relationship as a grid of PPFD × photoperiod cells, each colored and labeled with its DLI — a quick lookup table you can read like a chart.
Unit-conversion caveats
Foot-candles ↔ lux is an exact conversion (1 foot-candle = 10.764 lux), because both measure illuminance.
Lux → PPFD is an approximation. Lux is weighted to human eye sensitivity, while PPFD weights all PAR photons equally, so the conversion factor depends on the light's spectrum. A reading under sunlight, HPS, and white LED will each map to a different PPFD. [26] The calculator uses these per-source factors, for estimation only — for accuracy, measure PPFD with a quantum (PAR) sensor.
Where the crop numbers come from
Each crop range and planner preset on this site was assembled from the university extension tables and peer-reviewed studies listed below, and each one carries a short note on how its numbers were chosen. Two things to keep in mind when reading them:
- The "max" is usually a practical ceiling, not a biological one. For microgreens, lettuce, basil and cannabis, the studies found yield still rising at the top of the tested range. The upper bound here is where diminishing returns, heat and electricity cost make more light a poor trade, so it will move with your energy price and CO₂ level.
- Cultivar, temperature and CO₂ change the answer. The same DLI gives different results at 18 °C and 28 °C, with and without CO₂ enrichment, and across cultivars of the same crop. Use the ranges to get into the right zone, then tune on your own results.
Crop ranges
Purdue Table 2 puts Phalaenopsis, ferns, Maranta and Spathiphyllum at 2 (minimum), 4 (good) and 6–10 (high quality); low-light crops are defined as 3–6 mol/m²/day. [1]
Purdue recommends at least 10–12 for finishing; Virginia Tech lists impatiens 8–12, begonia and geranium 12–19, petunia 20–25; Faust et al. saw dry mass keep rising from 5 to 43 with diminishing returns above the mid-teens. [1, 4, 14]
Virginia Tech suggests 9–12. Jones-Baumgardt et al. found Brassica microgreen yield still increasing at 600 µmol/m²/s × 16 h (≈ 35 mol/m²/day), so the ceiling here reflects energy cost per tray, not a biological limit. [4, 10]
Cuttings rooted best toward the top of 1.2–10.7 (Lopez & Runkle); seedling quality improved up to about 12 (Pramuk & Runkle); tomato transplants did best at 13 (Huber et al.); Virginia Tech lists seedlings and cuttings at 5–10. [11, 12, 13, 4]
Cornell's CEA program grows lettuce to a constant 17 mol/m²/day for a 150 g head in 35 days; Virginia Tech lists 12–17; Baumbauer et al. found lettuce the most sensitive of the greens to DLI below 14. [5, 4, 6, 7]
Virginia Tech lists spinach 14–20; Baumbauer et al. saw spinach dry weight rise 42% from 8 to 14 mol/m²/day, less steeply than lettuce. [4, 6]
Kale dry weight rose 47% from 8 to 14 mol/m²/day with leaves getting smaller and thicker at higher DLI (Baumbauer et al.); range aligned with the spinach guidance in Virginia Tech's table. [6, 4]
Dou et al. tested 9.3–17.8 mol/m²/day: yield and phenolics rose throughout, with 12.9 suggested as the energy-efficient indoor point; Virginia Tech lists 15–25. [8, 4]
Virginia Tech lists parsley 10–15 and cilantro 15–20; Walters & Lopez modelled dill, parsley and watercress responses to DLI and temperature. [4, 9]
Ohio State's CEA berry guidance: minimum 10–12, optimum 20–25, stress above 30; Hidaka et al. roughly doubled greenhouse yield with LED supplemental light above 400 µmol/m²/s. [18, 17]
Purdue Table 2 rates tomato high quality at 22–30; Virginia Tech lists 20–30; Norwegian year-round production targets about 30 (Moe et al.); Dorais summarises the light response. [1, 4, 16, 15]
Purdue Table 2 rates Capsicum high quality at 22–30; Virginia Tech lists cucumber 20–30; Dorais summarises the light response of both crops. [1, 4, 15]
Moher et al. grew vegetative clones at 135–1,430 µmol/m²/s × 16 h: dry weight levelled off and plants became more compact as light rose; 30–40 mol/m²/day (≈ 460–620 µmol/m²/s at 18 h) sits on the flat part of that curve. [24, 20]
Flower yield rose linearly to 1,800 µmol/m²/s at 12 h (≈ 78 mol/m²/day) in Rodriguez-Morrison et al. and to at least 1,500 (≈ 65) in Eaves et al.; Llewellyn et al. confirmed proportional yield at 600–1,000 at commercial scale. Leaf photosynthesis peaks near 1,500 and gains ~50% with CO₂ at 750 ppm (Chandra et al.), which is why the top of the range assumes enrichment. [22, 21, 23, 19, 25]
Planner presets
Seedling and vegetative targets follow the propagation and vegetative-stage light studies (cuttings root best near 10 mol/m²/day; vegetative growth levels off around 30–40). Flowering targets sit on the linear yield-versus-PPFD relationship measured at 12 h, with the ripening stage eased back as leaf photosynthesis declines late in the cycle. The 18 h / 12 h photoperiods are the conventional short-day trigger; Ahrens et al. show 13–14 h also initiates flowering in many cultivars. [11, 24, 22, 23, 25]
Autoflowering cultivars are day-neutral, so the 18 h photoperiod is kept through flowering and the same per-stage DLI targets apply; the light-response data come from photoperiod cultivars, so treat this as an extrapolation. [24, 22, 21]
Germination and seedling targets follow the seedling DLI studies; the growth stage targets Cornell's 17 mol/m²/day lettuce integral and Virginia Tech's 12–17 range. 16 h photoperiods follow Kelly et al., who found longer days at lower PPFD out-yield short, bright days at the same DLI. [12, 5, 4, 7, 6]
Transplant stage targets 13 mol/m²/day after Huber et al.; vegetative, flowering and fruiting stages step up through the 20–30 range from Purdue Table 2 and Virginia Tech, toward the ~30 used in year-round Norwegian production. Photoperiod shortens toward 12 h in fruiting because tomato tolerates long days poorly. [13, 1, 4, 16, 15]
Sources
Numbered references used across the site. Each entry says what this site takes from it.
- 1.University extension
Torres, A.P. and Lopez, R.G. (2010). Measuring Daily Light Integral in a Greenhouse. Purdue Extension HO-238-W.
Used for: Definition of DLI, the low / medium / high / very-high light categories (3–6, 6–12, 12–18, >18), the 10–12 mol minimum for finishing shade-intolerant crops, and Table 2 (crop DLI requirements after J.E. Faust, Ball Red Book).
www.extension.purdue.edu/extmedia/ho/ho-238-w.pdf - 2.University extension
Runkle, E. (2006). Technically speaking: Daily light integral defined. Greenhouse Product News 16(11):70.
Used for: Plain-language definition of DLI and the PPFD × photoperiod relationship.
gpnmag.com/article/daily-light-integral-defined/ - 3.Peer-reviewed
Faust, J.E. and Logan, J. (2018). Daily Light Integral: A Research Review and High-resolution Maps of the United States. HortScience 53(9):1250–1257. doi:10.21273/HORTSCI13144-18
Used for: Review of crop responses to DLI and the outdoor DLI range (roughly 5–60 mol/m²/day across the US).
journals.ashs.org/view/journals/hortsci/53/9/article-p1250.xml - 4.University extension
Stallknecht, E. (2025). Calculating and Using Daily Light Integral (DLI): An Introductory Guide. Virginia Cooperative Extension SPES-720.
Used for: Table 3, suggested DLI by crop: seedlings and cuttings 5–10, microgreens 9–12, lettuce 12–17, spinach 14–20, parsley 10–15, cilantro 15–20, basil 15–25, tomato / cucumber 20–30.
www.pubs.ext.vt.edu/SPES/spes-720/spes-720.html - 5.Peer-reviewed
Albright, L.D., Both, A.-J. and Chiu, A.J. (2000). Controlling greenhouse light to a consistent daily integral. Transactions of the ASAE 43(2):421–431.
Used for: The Cornell CEA lettuce target: a constant 17 mol/m²/day produced a 150 g marketable head 35 days after seeding.
elibrary.asabe.org/abstract.asp?JID=3&AID=2721&CID=t2000&v=43&i=2&T=1 - 6.Peer-reviewed
Baumbauer, D.A., Schmidt, C.B. and Burgess, M.H. (2019). Leaf Lettuce Yield Is More Sensitive to Low Daily Light Integral than Kale and Spinach. HortScience 54(12):2159–2162. doi:10.21273/HORTSCI14288-19
Used for: Kale, leaf lettuce and spinach grown at 8, 10, 12 and 14 mol/m²/day: dry weight rose linearly with DLI (lettuce +203%, kale +47%, spinach +42%).
journals.ashs.org/view/journals/hortsci/54/12/article-p2159.xml - 7.Peer-reviewed
Kelly, N., Choe, D., Meng, Q. and Runkle, E.S. (2020). Promotion of lettuce growth under an increasing daily light integral depends on the combination of the photosynthetic photon flux density and photoperiod. Scientia Horticulturae 272:109565.
Used for: Lettuce yield increases with DLI, and a longer photoperiod at lower PPFD can out-yield the same DLI delivered in fewer hours.
www.sciencedirect.com/science/article/abs/pii/S0304423820303939 - 8.Peer-reviewed
Dou, H., Niu, G., Gu, M. and Masabni, J.G. (2018). Responses of Sweet Basil to Different Daily Light Integrals in Photosynthesis, Morphology, Yield, and Nutritional Quality. HortScience 53(4):496–503. doi:10.21273/HORTSCI12785-17
Used for: Sweet basil at 9.3, 11.5, 12.9, 16.5 and 17.8 mol/m²/day: yield and phenolics rose with DLI; the authors suggest 12.9 as the energy-efficient indoor target.
journals.ashs.org/hortsci/view/journals/hortsci/53/4/article-p496.xml - 9.Peer-reviewed
Walters, K.J. and Lopez, R.G. (2021). Modeling growth and development of hydroponically grown dill, parsley, and watercress in response to photosynthetic daily light integral and mean daily temperature. PLOS ONE 16(3):e0248662.
Used for: DLI × temperature response of culinary herbs; basis for the general herb range.
journals.plos.org/plosone/article?id=10.1371/journal.pone.0248662 - 10.Peer-reviewed
Jones-Baumgardt, C., Llewellyn, D., Ying, Q. and Zheng, Y. (2019). Intensity of Sole-source Light-emitting Diodes Affects Growth, Yield, and Quality of Brassicaceae Microgreens. HortScience 54(7):1168–1174.
Used for: Kale, cabbage, arugula and mustard microgreens under 100–600 µmol/m²/s for 16 h (≈ 6–35 mol/m²/day): fresh weight kept rising to the top of the range.
journals.ashs.org/view/journals/hortsci/54/7/article-p1168.xml - 11.Peer-reviewed
Lopez, R.G. and Runkle, E.S. (2008). Photosynthetic Daily Light Integral during Propagation Influences Rooting and Growth of Cuttings and Subsequent Development of New Guinea Impatiens and Petunia. HortScience 43(7):2052–2059.
Used for: Cuttings rooted under 1.2–10.7 mol/m²/day: root and shoot mass rose steeply with DLI, and higher DLI shortened time to a marketable liner.
journals.ashs.org/hortsci/view/journals/hortsci/43/7/article-p2052.xml - 12.Peer-reviewed
Pramuk, L.A. and Runkle, E.S. (2005). Photosynthetic Daily Light Integral during the Seedling Stage Influences Subsequent Growth and Flowering of Celosia, Impatiens, Salvia, Tagetes, and Viola. HortScience 40(5):1336–1339.
Used for: Seedlings at 4.1–14.2 mol/m²/day: transplant quality improved as DLI rose to about 12.
journals.ashs.org/hortsci/view/journals/hortsci/40/5/article-p1336.xml - 13.Peer-reviewed
Huber, B.M., Louws, F.J. and Hernández, R. (2021). Impact of Different Daily Light Integrals and Carbon Dioxide Concentrations on the Growth, Morphology, and Production Efficiency of Tomato Seedlings. Frontiers in Plant Science 12:615853. doi:10.3389/fpls.2021.615853
Used for: Tomato transplants at 6.5, 9.7 and 13.0 mol/m²/day: 13.0 was best; CO₂ enrichment let 9.7 match it.
www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.615853/full - 14.Peer-reviewed
Faust, J.E., Holcombe, V., Rajapakse, N.C. and Layne, D.R. (2005). The Effect of Daily Light Integral on Bedding Plant Growth and Flowering. HortScience 40(3):645–649.
Used for: Eight bedding-plant species grown at 5–43 mol/m²/day: shoot and flower dry mass increased across the whole range, with diminishing returns above the mid-teens for most species.
journals.ashs.org/hortsci/view/journals/hortsci/40/3/article-p645.xml - 15.Reference
Dorais, M. (2003). The use of supplemental lighting for vegetable crop production: light intensity, crop response, nutrition, crop management, cultural practices. Canadian Greenhouse Conference, Toronto, 9 Oct 2003.
Used for: Light-response summary for greenhouse tomato, cucumber and pepper that most later DLI tables cite.
www.researchgate.net/publication/284348452_Physiological_response_of_greenhouse_vegetable_crops_to_supplemental_lighting - 16.Peer-reviewed
Moe, R., Grimstad, S.O. and Gislerød, H.R. (2006). The use of artificial light in year round production of greenhouse crops in Norway. Acta Horticulturae 711:35–42.
Used for: Year-round tomato and cucumber production targets around 30 mol/m²/day under supplemental HPS.
www.actahort.org/books/711/711_2.htm - 17.Peer-reviewed
Hidaka, K., Dan, K., Imamura, H., Miyoshi, Y., Takayama, T., Sameshima, K. et al. (2013). Effect of supplemental lighting from different light sources on growth and yield of strawberry. Environmental Control in Biology 51(1):41–47. doi:10.2525/ecb.51.41
Used for: Strawberry yield roughly doubled under LED supplemental light above 400 µmol/m²/s compared with unlit control.
www.jstage.jst.go.jp/article/ecb/51/1/51_41/_article/-char/en - 18.University extension
Ohio State University, Controlled Environment Berry Production Information: Photosynthetic lighting.
Used for: Strawberry DLI guidance: minimum 10–12, optimum 20–25, stress above about 30 mol/m²/day.
u.osu.edu/indoorberry/photosynthetic-lighting/ - 19.Peer-reviewed
Chandra, S., Lata, H., Khan, I.A. and ElSohly, M.A. (2008). Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO₂ conditions. Physiology and Molecular Biology of Plants 14(4):299–306.
Used for: Leaf photosynthesis peaked at 1,500 µmol/m²/s and 30 °C; raising CO₂ from 350 to 750 ppm lifted net photosynthesis by about 50%.
pmc.ncbi.nlm.nih.gov/articles/PMC3550641/ - 20.Peer-reviewed
Chandra, S., Lata, H., Mehmedic, Z., Khan, I.A. and ElSohly, M.A. (2015). Light dependence of photosynthesis and water vapor exchange characteristics in different high Δ⁹-THC yielding varieties of Cannabis sativa L. Journal of Applied Research on Medicinal and Aromatic Plants 2(2):39–47.
Used for: Four drug-type varieties measured at 0–2,000 µmol/m²/s; photosynthesis kept responding at high PPFD.
www.sciencedirect.com/science/article/abs/pii/S2214786115000078 - 21.Peer-reviewed
Eaves, J., Eaves, S., Morphy, C. and Murray, C. (2020). The relationship between light intensity, cannabis yields, and profitability. Agronomy Journal 112(2):1466–1470. doi:10.1002/agj2.20008
Used for: Flower yield rose linearly with PPFD to at least 1,500 µmol/m²/s (≈ 65 mol/m²/day at 12 h) and the extra electricity paid for itself.
acsess.onlinelibrary.wiley.com/doi/abs/10.1002/agj2.20008 - 22.Peer-reviewed
Rodriguez-Morrison, V., Llewellyn, D. and Zheng, Y. (2021). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. doi:10.3389/fpls.2021.646020
Used for: Flowering under 120–1,800 µmol/m²/s at 12 h: dry inflorescence yield increased linearly all the way to 1,800 (≈ 78 mol/m²/day), while leaf photosynthesis saturated far lower.
www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.646020/full - 23.Peer-reviewed
Llewellyn, D., Golem, S., Foley, E., Dinka, S., Jones, A.M.P. and Zheng, Y. (2022). Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. doi:10.3389/fpls.2022.974018
Used for: Commercial-scale flowering at 600, 800 and 1,000 µmol/m²/s (≈ 26–43 mol/m²/day at 12 h): yield proportional to PPFD.
www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.974018/full - 24.Peer-reviewed
Moher, M., Llewellyn, D., Jones, M. and Zheng, Y. (2022). Light intensity can be used to modify the growth and morphological characteristics of cannabis during the vegetative stage of indoor production. Industrial Crops and Products 183:114909.
Used for: Vegetative clones under 135–1,430 µmol/m²/s for 16 h (≈ 8–82 mol/m²/day): dry weight rose then levelled off; plants got shorter, thicker and more compact with more light.
www.sciencedirect.com/science/article/abs/pii/S0926669022003922 - 25.Peer-reviewed
Ahrens, A., Llewellyn, D. and Zheng, Y. (2023). Is Twelve Hours Really the Optimum Photoperiod for Promoting Flowering in Indoor-Grown Cultivars of Cannabis sativa? Plants 12(14):2605. doi:10.3390/plants12142605
Used for: Ten cultivars flowered under 12–15 h photoperiods; several initiated normally at 13–14 h, so 12 h is a floor rather than an optimum.
www.mdpi.com/2223-7747/12/14/2605 - 26.Peer-reviewed
Thimijan, R.W. and Heins, R.D. (1983). Photometric, Radiometric, and Quantum Light Units of Measure: A Review of Procedures for Interconversion. HortScience 18(6):818–822.
Used for: The standard reference for converting lux, W/m² and µmol/m²/s per light source, and why the factor is spectrum-dependent.
journals.ashs.org/hortsci/view/journals/hortsci/18/6/article-p818.xml - 27.Reference
Apogee Instruments. Conversion – PPFD to Lux (technical note, based on measured lamp spectra).
Used for: Lux per µmol/m²/s: sunlight 54 (0.0185), cool-white fluorescent 74 (0.0135), mogul HPS 82 (0.0122), metal halide 71 (0.0141), ceramic metal halide 4200 K 65 (0.0154).
www.apogeeinstruments.com/conversion-ppfd-to-lux/ - 28.Reference
Sharakshane, A. (2018). An easy estimate of the PFDD for a plant illuminated with white LEDs: 1000 lx = 15 µmol/s/m². bioRxiv preprint. doi:10.1101/289280
Used for: White-LED rule of thumb of 15 µmol/m²/s per 1,000 lux (factor 0.015), derived from phosphor-LED spectra across 2700–6500 K.
www.biorxiv.org/content/10.1101/289280v1