What is the DLI (Daily light integral) and how is it calculated

Daily Light Integral (DLI) indicates the amount of light that a crop can use within a 24-hour window. Understanding and optimizing DLI is essential for healthy plants and high yields.

What is DLI? 
The DLI is a measurement based on the PPFD method (see the article on what is PPFD). The DLI measures the photosynthetically active photons hitting the plant in a specific area, within a 24 hour window.

The light provided by the sun differs according to the geographic location and the time of year

Plants capture photons (the photon is the quantum of energy of electromagnetic radiation, also called the quantum of light) and convert them into energy with the help of chlorophyll and carotenoid - carotenoids help chlorophyll molecules absorb light in photosynthesis. Carotenoids also absorb excess light when it reaches dangerous levels.
The synthetically active photons are limited to light radiation which falls within the range of 400-700 nm. It is this type of light that plants use. When light leaves this range, it is essentially useless.

Instead of going into complicated calculations, let's skip the technical aspects for now and find out how DLI is beneficial to plants.

Why is light so important for plants?
Light is the primary driving force for all photosynthetic plants. Although other factors, such as the medium in which they are anchored, roots and humidity are extremely essential, light plays a fundamental role for most plants. Light powers every process of the plant, such as root growth, flower production and vegetative growth. The DLI measures the amount of light per day that plants use to reach their potential and that is why it is so crucial. Where we have a growing environment with too little light the plant will be fragile and weak, while too much light will damage it and prevent it from proceeding further in the photosynthesis process. Both of these conditions will result in poor yield.

All plants have optimal (or maximum) DLI. Knowing the optimal DLI of the plant allows you to adjust the daily photon requirement within a correct range. This is also absolutely necessary for greenhouse crops and just as often the farmer regulates this requirement instinctively, but based on experience.

Optimal lighting is essential for plant growth

Plants have different DLI requirements based on their natural habitat. A plant that grows on the ground in the jungle has a significantly lower DLI than that of a palm tree that receives an enormous amount of dazzling sunshine.

Let's take a look at the DLI of some crops that are commonly grown indoors.

PlantDLI
Lettuce14 – 16
Peas9
Basil12
Broccoli15 – 35
Tomatoes20 – 30
Zucchini25
Peppers30 – 40
Cannabis30 – 45
DLI = PPFD (μmol / m2) x 3,600 (s / h) x photoperiod (hours / day)

From this formula it is possible to derive both the PPFD value needed to reach a desired quantity of DLI, and the hours of light necessary for the correct lighting of a plant.

With regard to the DLI it is good to specify that in greenhouses, about half of the amount of natural light used is altered at the time of entry into the greenhouse, due to the absorption caused by the structure and the covering material. 

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Calculate the DLI (Daily light integral) of the greenhouse you have in mind. Starting from the Italian geographical area concerned and knowing the limiting factors, in terms of the reduction of light radiation determined by the structure and material chosen as roofing, you can calculate the DLI of your project.

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Naturae Plena

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