Daily Light Integral Calculator

Created by Komal Rafay
Reviewed by Łucja Zaborowska, MD, PhD candidate and Adena Benn
Last updated: Mar 24, 2023

The DLI or daily light integral calculator is here to tell you that there is more to plants than we know. Like there can be other light sources for a plant to be photosynthetically active. I bet that came as a surprise!

There is no need to worry because after reading this article, you will know what we mean by other sources of light. We will be discussing everything about DLI, from PPF (photosynthetic photon flux) and PPFD(photosynthetic photon flux density) to the value and formula of DLI.

We will ensure you are efficient in calculating the value even without using a DLI calculator.

What is DLI?

DLI stands for Daily Light Integral, and for the conciseness of this article, we will refer to it as DLI.

The light that plants absorb daily is a variable we can measure. And that is where DLI comes in. It measures the light a plant gets daily. This light doesn't have to be from the sun only. In the world of horticulture (a branch of agriculture that deals with the art, technology, and aesthetics of plant cultivation), the DLI holds significance because they use artificial means of light to ensure plants perform photosynthesis. We all know the importance of photosynthesis, as it is the process by which plants produce oxygen and energy for their food using sunlight, water, and carbon dioxide.

DLI is an incremental measure of the sum of photons that reach plants in their photoperiod(the daylight a plant/organism receives in a day).

The unit to measure the DLI value is mol/m²/day, the number of moles of photons per square meter per day.

What is PPFD?

PPFD stands for photosynthetic photon flux density.

PPFD measures the number of photosynthetically active photons that fall on a given plant surface per second. The unit to measure PPFD is μmol/s·m².

The value of PPFD is of major significance for horticulturalists and greenhouses, as they use it as a base to measure the intensity of light sources to grow plants without the sun.

We suggest you try out our photon energy calculator so you can explore the relationship between the wavelength and frequency of the photon and its energy.

Daily light integral calculator

Daily light integral and photosynthetic photon flux density sound heavy, which is one of the reasons we made sure that our tool is nothing but the opposite of heavy. By that, we do not mean light, but we guarantee it is easy to use and understand.

So to start, there are only two things you need to know to get the value of DLI:

  1. Input the light hours in a day. There is a list of units to choose from. The default value is hours.
  2. Next, input the PPFD value as μmol/s·m².
  3. Now, it is up to the tool to display the resultant DLI as mol/m²/day.

Let's consider an example to ensure that our daily life integral calculator produces the results we promise it does.

For instance, you input the light hours in a day as 9 hours and the photon flux density as 1500 μmol/s·m². The calculator displays the DLI to be 48.6 mol/m²/day.

A nice idea would be to give our plant spacing calculator a try. It helps you navigate how to calculate plant spacing in that critical planning stage.

DLI formula

The formula for DLI uses the photosynthetic photon flux density and the daily light hours to estimate the value of DLI:

dli = ppfd × lhd × 3600 / 1000000


  • dli – Daily light integral;
  • ppfd – Photosynthetic photon flux density; and
  • lfd – Light hours in a day.

How to calculate DLI

Now that we are familiar with the DLI formula, we can prepare ourselves to face a situation where we don't have access to the daily light integral calculator, like if the teacher asks in a pop quiz.

So, by following these steps, you can determine the DLI value by yourself.

  1. Note down the number of light hours.
  2. Note down the PPFD value in μmol/s·m².
  3. Multiply the light hours by PPFD.
  4. Multiply the result by 3600.
  5. Next, divide the result from step 4 by 100,000.
  6. The result is the DLI value in mol/m²/day.

Significance of DLI

The DLI impacts plants in several ways; hence is significant. It is an efficient means to execute supplemental lighting in greenhouses.

It has a notable influence on the following:

  • Growth of roots;
  • Growth of shoots of plants;
  • Stem girth;
  • Height of the plant;
  • The branching pattern;
  • Number of flowers; and
  • Flowering times.

These are also the attributes that influence crop quality and yield.

For the growth of seedlings and baby plants, the recommended DLI is 6 - 8 mol/m²/day. Its gradual increase is the need for growing plants.

Use the plant population calculator to calculate the number of plants you can grow in your farm field and make early yield and profit estimates.


What happens if the DLI value is low?

A low DLI value means the plants are not getting enough light. It could cause slow growth and retarded photosynthesis. As a result, slower food production.

In some plants like tomatoes, a low DLI can cause the fruit to be dry and flavorless.

Is PPF the same as PPFD?

No, they are not. They might seem the same, but they have a crucial difference.

They both measure the amount of light from a source of light. But the difference is that PPFD (photosynthetic photon flux density) measures the density of the photons falling on a surface, whereas PPF (photosynthetic photon flux) measures the total number of photons a light source emits.

What is the unit of DLI?

The unit of the daily light integral is mol/m²/day.

It means that the DLI gauges the number of moles of photons per square meter per day.

Is PPFD important for calculating DLI?

The PPFD(photosynthetic photon flux density) determines the number of photosynthetically active photons falling on the plant every second. Hence, becoming a vital part of estimating the DLI value.

It is part of the DLI formula as:

dli = ppfd × lhd × 3600 / 1000000


  • dli – Daily light integral;
  • ppfd – Photosynthetic photon flux density; and
  • lfd – Light hours in a day.

How can I calculate the DLI value?

You may calculate the DLI(daily light integral) value by following the steps given below:

  1. Multiply the PPFD(photosynthetic photon flux density) by the daily light hours.
  2. Multiply the result by 3600.
  3. Divide the result from step 2 by 1000000.
  4. The result is the DLI value as mol/m²/day.

What is the DLI value with 11 hours of light?

The DLI (daily light integral) value is 87.12 mol/m²/day if we suppose the photosynthetic photon flux density value is 2200 μmol/s·m².

Komal Rafay
Light hours per day
Photon flux density (PPFD)
Daily light integral (DLI)
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