Daily Light Integral (DLI) Info & Calculator

Daily Light Integral (DLI) is a measure used in horticulture to quantify the total amount of photosynthetically active radiation (PAR) received by a plant over the course of a day. PAR refers to the spectrum of light wavelengths (400-700 nm) that plants use for photosynthesis. DLI is expressed in units of moles of photons per square meter per day (mol/m²/day). It provides a comprehensive measure of the total amount of light energy available to plants for photosynthesis during a 24-hour period. DLI considers both the intensity and duration of light exposure, offering a more complete understanding of the light environment for plant growth.

When calculating DLI, two factors are crucial.

  • Photosynthetic Photon Flux Density (PPFD):

PPFD is a measure of the amount of light that is available for photosynthesis to occur in a specific area over a given time. PPFD is typically expressed in units of micromoles of photons per square meter per second (μmol/(m²·s)). PPFD is an important metric because it helps quantify the intensity of light that plants receive. PPFD provides an accurate measurement of the specific wavelengths of light that are most effective for photosynthesis.

  • Photosynthetic Photon Flux (PPF):

PPF is a measure of the total amount of photosynthetically active photons emitted by a light emitting diode (LED) light source in any given period. PPF is expressed in micromoles per second (μmol/s). The closer the LED is to your plants, the higher the concentration of photons will be.

Daily Light Integral (DLI):

DLI measures how much light a plant has received during one full day. This metric is employed to guarantee that your plants receive the intended quantity of light. As much as 95% of your plant’s final dry weight is derived from photons (light) rather than fertiliser inputs. DLI is the foremost factor in maximising yield.

DLI for different plant types:

Each species of plant will have differing DLI requirements for healthy growth. Low light plants require a DLI between 5-10, medium light plants a DLI of 10-15, and high light plants will require a DLI of more than 15 and as high as 40.

CO₂ Enrichment:

Photosynthesis is enhanced in high CO₂ environments. Growers will aim for higher DLIs to maximise the benefits of increased carbon dioxide availability. Monitoring and adjusting both light levels and CO₂ concentrations are key aspects of optimising plant growth in controlled environments.

A list of DLI requirements for many plant species is included. Click on DLI Levels For Plants below for a downloadable PDF.

Setting up your PRO GROW LED for correct DLI:

There are three factors that determine the DLI delivered to your plants.

  • The maximum PPF output of the LED fixture
  • The distance between your LED and the plant canopy
  • Manually dimming your LED

PRO GROW LED fixtures typically boast a greater PPF output compared to our competitors with a similar power output (Watts). Consequently, we strongly advise adhering to the suggested fixture heights outlined in our PPFD User Guide. For enhanced precision, utilise the DLI calculator provided below. Keep in mind that excessive light at inappropriate times can harm plants through oversaturation or photobleaching, leading to hindered growth and diminished yields. In such cases, it is not a fault of the LED but rather operator error.

Medicinal cannabis production:

In response to requests from licensed commercial facilities, we have developed a comprehensive weekly DLI chart specifically tailored for cannabis. Given the subtle differences among phenotypes, it is essential to exercise caution when applying the recommended DLI from our chart. The occurrence of leaf cupping, characterised by leaf edges curling up and inward, is an indication that the DLI is too high for the current growth stage or phenotype. Should this happen, it is advisable to reduce light intensity until regular leaf growth is observed.

Calculating DLI:

To use the calculator simply enter the PPFD, then the hours of light you are providing per day. The DLI will be calculated for you.

How do I determine the correct PPFD figure to enter?

There are two ways to determine the PPFD of your LED light source.

  1. Use a quality light meter:

    To accurately measure PPFD, purchase a quality light meter that reads in PPFD. When using a PPFD meter, take multiple readings at the upper layer of leaves and branches of the plant canopy.

  2. Use the PRO GROW PPFD User guide:

    The PRO GROW PPFD user guide tells you the PPFD of each fixture at a certain distance. As the distance from LED to plant canopy decreases, the PPFD gets higher. Enter the PPFD figure that is recommended for each stage of growth and make sure that your LED is at the recommended height listed for the corresponding week.

To access the PPFD User Guide click on the link below.

DLI Plant Guide
Medicinal Cannabis Guide
PPFD User Guide

DLI Calculator

DLI = 15