DLI (Daily Light Integral) Chart - Understand your plants' PPFD & photoperiod requirements

[Updated 02 March 2021]

 

How intense light (PPFD) to expose various species to and for how long.

Light intensity, or rather, how densely packed light is with photons, is measured in micromoles per meter squared per second, µmol/m2/s. This is called PPFD (Photosynthetic Photon Flux Density). Intense light has high PPFD and low-intense light has low PPFD. During bright daylight in a warm and sunny place, the sun's PPFD level hitting the earth is around 2000. During the evening, before sundown, it's down to 500-1000. During dark nights, close to zero.



Some plants thrive in warm climates while others do better in cold and shaded places. This means that some plants prefer intense sunlight (high PPFD) while others prefer less intense (low PPFD). Same goes for our everyday vegetables, herbs, fruits, houseplants, and flowers.
Time is also a factor. Low intense light but over a long period results in the same number of photons as twice the light intensity but only during half as long period of time. This is especially important to indoor grows where the light output of a grow light and its photoperiod (how long the light is on) can easily be regulated.

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Understanding PPFD and DLI is essential to successfully setup an efficient grow. Whether it's a small grow with a single basil plant in the window sill, a grow tent with LED grow lights and various vegetables, or a greenhouse illuminated by the sun, DLI should be accounted for. Too high DLI numbers will burn a plant while too low numbers will hinder its growth potential.

 

Closet vegetable grow with LEDTonic Q2



We've made it easy for you to calculate the DLI exposure your plants are receiving based on PPFD levels and photoperiod. The PPFD levels produced by your grow light should be supplied by the manufacturer. Adjust the lamp height-wise from the plant to achieve desired PPFD levels, then set how long period of time the lamp should be operational for, each day.

Find the DLI recommendations for common plants below. Supplied kindly by Erik Runkle (professor and floriculture Extension specialist in the department of horticulture at Michigan State University) and Dr. Lynette Morgan (B. Hort. Tech. degree and a PhD in hydroponic greenhouse production from Massey University, New Zealand. Lynette is a partner with Suntec International Hydroponic Consultants and has authored several hydroponic technical books. Visit suntec.co.nz for more information). Full credit and many thanks to both of these scientists.

Daily light integral (DLI) describes the number of photosynthetically active photons (individual particles of light in the 400-700 nm range) that are delivered to a specific area (1m2) over a 24-hour period.
The formula for calculating DLI is: μmol m-2s-1 (or PPFD) x (3600 x photoperiod) / 1,000,000 = DLI (or moles/m2/day)
PPFD is the number of photons that arrive at a specific area (m2) every second, measured in micromoles (μmol m-2s-1).
1.000.000 micromoles = 1 mole
3600 seconds = 1 hour

The number of moles per hour, per m2, multiplied with photoperiod (the number of hours with that intensity) = DLI, Daily Light Integral

DLI chart (PPFD & photoperiod) by LEDTonic
Erik Runkle:
Crop DLI
Vegetative cuttings (liners) - early 4-6
Vegetative cuttings (liners) - late 6-10
Seedlings (plugs) - early 6-10
Seedlings (plugs) - late
10-15
Shade plants (annuals and perennials) 6-10
Foliage plants 6-10
Potted bulbs 6-15
Stock plants (for cuttings)
10-20
Annual bedding plants 10+
Leafy greens and herbs 12+
Potted flowering plants 12+
Shrubs 12+
Cut flowers 15+
Fruiting vegetables

15+

 

Dr, Lynette Morgan:
Crop DLI
Violets, orchids, ferns 4-6
Seedlings/cuttings 6-8
Small herbs
10-12
Butterhead lettuce
14-16
Cucumber
20-30
Capsicum
20-30
Eggplant
20-30
Tomatoes
22-30

 
How to find the right LED grow light
LEDTonic Q2 LED grow light in a 2x2' tent growing mango, peppers, ginger, basil, and lemon. The lamp is hanging approximately 10"/25 cm above the plants, delivering around PPFD 300 µmol/m2/s in the center. At 18 hours of light per day, 19.4 DLI is achieved.


>> How To Find  the Right LED Grow Light (blog)

>> LEDTonic LED Grow Lights


Example:
You are growing cucumbers and want to give them around 25 DLI.
Your grow light produces 500 PPFD at 18" from the plant according to your grow light PPFD map/light footprint.
If the lamp's distance is increased to 20" from the plant, it produces 400 PPFD at the canopy.
If the lamp is lowered to 15", it produces 700 PPFD.

By looking at the chart we see that ~25 DLI is achieved by exposing the plant to 500 PPFD over 14 hours but also when exposing the plant to 400 PPFD over 17 hours or 700 PPFD over 10 hours.
Choose a combination that fits both your grow set up but also your plant's minimum and maximum PPFD limits. Very high PPFD levels over a short duration of time or very low PPFD levels over a long duration of time are rarely ideal for good growth.


 

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15 comments

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Max - LEDTonic

Hello Wei,

Light particles (photons) are like water droplets, in a way. Light footprints that overlap will add up and 100 PPFD + 100 PPFD = 200 PPFD.
As example, we’ve measured our Z5 LED grow light in different positions inside a reflective space. By mirroring the results and adding them together, we can see how two lamps perform and how their footprints overlap at different distances.

Light footprint comparison:
https://i.imgur.com/NjTXSD5.jpg

Wei Kee Keoh

Hello,
I am very new to indoor growing and I have a question regarding light. I am trying to grow lettuce indoor at the moment. The market available that I have access to is 4ft T8 LED grow light, with PPFD value of 150 umol/m2/s at 15cm, which gives 6.48 DLI in 12 hours. I understand that much lettuce need DLI of at least 12. Since installation of T8 LED grow light will be side by side, so my question is, will these overlapping of light compensate with the low PPFD? Or do I really need to source for a light that gives PPFD of at least 250 umol/m2/s?

Jesús Bejarano

Thanks for so clear explanation.

Douglas

I just had to post up and say thank you so much for the clear explanation and awesome chart. This information is golden and when not growing Cannabis there is just so little out there that doesn’t require a PHD to decipher.
Buying LED lights that fit the needs of Pepper Growers doesn’t require them to buy the latest tech and pay new tech prices. More lights make more sense and a more forgiving footprint. Thanks again.

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