The importance of DLI

By measuring the Daily Light Integral, or DLI, grounds managers can assess whether additional lighting is needed, especially in shaded areas, to supplement natural sunlight and promote healthy grass growth. Monitoring DLI levels is essential for maintaining high-quality grass playing surfaces and ensuring optimal plant health.

What is DLI?

The DLI is a unit that represents the total amount of PAR available to a grass plant at a specific location on the field throughout the day. It is usually expressed as moles of light (mole photons) per square meter (m²) per day (d1) or mole * m² * d1.

For optimal growth, a grass plant requires a specific amount of light. Specifically, this involves Photosynthetically Active Radiation (PAR, 400 – 700nm), which is the portion of the sun’s light spectrum used by plants for photosynthesis and is crucial for grass plant growth.

DLI is measured per day and not per second. This is because there can be a lot of variation in light within a day (day/night and cloudy/clear skies), and an indication per 24 hours thus provides a better picture of the situation.

Why is DLI used for grass lighting systems?

By calculating the DLI, it can be determined whether the grass plant is receiving enough light for healthy growth, and thus whether additional light is needed.

If the calculation reveals that natural sunlight alone is insufficient for optimal grass growth, it can be determined, based on the calculated DLI, to what extent an additional light source – in the form of grass growth lighting units – is needed to create the optimal conditions for maximum grass growth after a training session or game.

The DLI also tells a grounds manager how much extra light a grow lighting unit radiates. DLI is an important variable that is considered in our growth model and thus partially determines which solution we believe is the best fit.

The SGL LED440 on the pitch at the Johan Cruijff ArenA.

How can you calculate DLI?

To calculate the DLI, you first need to know the Photosynthetic Photon Flux Density (PPFD). PPFD is expressed in micromoles of photons per square meter per second (micromole/m²/s) and can be measured using a PPFD meter.

Convert the measured PPFD value into a 24-hour value: μmol/m²/s * 60 seconds * 60 minutes * 24 hours.

Convert the calculated value into moles by dividing by 1,000,000 and you’ll get mol/m²/day, or DLI.

Example calculation

For example, the light output (PPFD) of an LED440 is measured at 354 μmol/m²/s. This is the average light level across 440 square meters.

  1. Calculate the value per day by multiplying 354 by the number of seconds in a day. Then you will have the amount of μmol/m²/day.
    (354 * 60 * 60 * 24 = 30,585,600)
  2. To get to mol/m²/day, divide the amount of μmol/m²/day by 1,000,000.
    30,585,600 / 1,000,000 = 30.58 mol/m²/day.
  3. Using the LED440 for 24 hours in the same location will provide an additional 30,58 mol/m² on that part of the playing surface.

If you want to calculate the DLI for the other SGL LED grow lighting units, i.e., the LED120 and the LED50, you can use the light output provided on the respective product pages.

What are the DLI requirements?

The amount of light a grass plant needs during the day depends on various variables. Grass species and the hours of playing surface usage are among the most important factors influencing these requirements. Every situation brings its unique challenges and opportunities. Through a comprehensive analysis of the growth conditions and detailed growth algorithm, we can accurately determine the specific needs of the grass. Schedule a meeting with one of our agronomists to discover how you can create a microclimate for optimal grass growth.