Enter the total PPFD and the light hours per day into the calculator to determine the daily light integral (DLI).

DLI Formula

The following formula is used to calculate a DLI.

DLI = PPFD* LFD * (3600/1,000,000)
  • Where DLI is the daily light integral (mol/m^2/d)
  • PPFD is the photosynthetic photon flux density (umol/s*m^2)
  • LFD is the light hours per day

DLI Definition

DLI stands for daily light integral, and it is a measure of the total number of photosynthetically active photons (those in the range of 400-700nm) that are delivered to an area over a given period.

Example Problem

How to calculate DLI?

  1. First, determine the total number of light hours per day.

    For this example, the total number of light hours the area receives per day is 10 hours.

  2. Next, determine the PPFD.

    In this case, the photosynthetic photon flux density is found to be 15 umol/s*m^2.

  3. Finally, calculate the DLI.

    Using the formula above, the daily light integral is found to be:
    DLI = PPFDl * LFD * (3600/1,000,000)
    DLI = 10 * 15 * (3600/1000000)
    DLI = .54 mol/m^2/day


What is PPFD and how does it affect plant growth?

PPFD stands for Photosynthetic Photon Flux Density. It measures the amount of PAR (Photosynthetically Active Radiation) that reaches a plant’s surface in one second. This metric is crucial for understanding how much light a plant receives, as it directly influences photosynthesis rates, and consequently, plant growth and health.

Why is the Daily Light Integral (DLI) important in agriculture?

The DLI is a measure of the total quantity of usable light (photons) that plants receive in a day. It is significant in agriculture because it helps farmers and growers optimize light exposure for their crops, ensuring that plants receive the appropriate amount of light for healthy growth and maximum yield. Monitoring and adjusting DLI can lead to more efficient use of light resources and better crop performance.

How can adjusting the light hours per day impact DLI and plant growth?

Adjusting the light hours per day can significantly impact the DLI and, consequently, plant growth. Increasing light hours can raise the DLI, promoting faster growth and shorter production cycles in some plant species. Conversely, reducing light hours can decrease the DLI, which might be beneficial for species that require lower light intensities or for managing flowering times. Careful management of light hours is essential for optimizing plant health and yield.