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

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.

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.



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 & photperiod) 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

 


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 chart/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's producing 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.


6 comments

Max - LEDTonic

Hermann,

Try this phrase in Google:
Light requirements for aquatic plants + PPFD

The simplified general answer seems to be 30-40 PPFD on average.

Max - LEDTonic

C.Rosenthal,

Google tells me that ficus carica perform best in full sun. 500 PPFD x 16h will give you around 29 DLI which is a great level of light for full-sun species. Keep in mind that it’s often better to increase the light intensity gradually over a longer period of time than to suddenly increase from very low light intensities and short photoperiod, to the very opposite. In other words, it may be wise to start with 250 PPFD x 16h and work your way upwards from there.

Max - LEDTonic

Hello Jesse,

When we measure light intensity, we measure how many micromoles of photosynthetically active radiation that lands on a square meter, each second.

As the sensor is rather small, about an inch (2cm) in diameter, it only takes a spot measurement. The intensity measured, for example, 200 µmol/m2/s (PPFD), is how many photons that would land on a whole square meter each second if the light intensity was evenly distributed from the light source and equal to the light intensity measured at that spot. This is true when we are measuring the sun, a light source that is very far away, as moving the sensor sideways will still show us the same value outdoors. This doesn’t apply for smaller light sources. The smaller the light source and the closer it is to the sensor, the larger changes we will see in PPFD when moving the sensor sideways. This is why it is important to take several spot measurements that paint the full picture and show not only how intense light is right below the lamp, but also at X distance sideways.

What you want to know is what spot-intensity your plant is experiencing. If you move your plant sideways below the lamp and it receives lower light intensities, that will also result in a lower DLI value. Plants don’t care about how much light is produced in total, they only care about how much light they are actually receiving.

I hope this gave some clarity. Please let us know if anything was confusing.
Also, feel free to share some more information about your specific situation and we can help you calculate your lighting needs. You can always reach out to us at support@ledtonic.com

C.Rosenthal

Hi. What would the DLA be for a common fig plant – Ficus carica

Jesse Nichols

Does DLI, which is measured by the sq meter, translate directly to a sq foot calculation if you multiply the DLI by 0.0929 (which is the proportion of sq ft to sq meter), or is this an average that you need to maintain no matter if the space is a square meter, square foot, etc?

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