Background
Daily light integral (DLI) and photosynthetic photon flux density (PPFD) data is important to greenhouse production because they measure the amount of light that is available to the crop. This data can be used to adjust the growing environment, such as irrigation and carbon dioxide levels, to optimize photosynthesis and crop yield.
DLI is the total amount of light within the photosynthetically active radiation (PAR) spectrum (light wavelengths of 400-700 nm) that impacts a surface in a day. It is measured in moles per metre squared per day (mol/m2/day).
PPFD is the total amount of light within the PAR spectrum that impacts a surface every second. It is measured in micromoles per metre squared per second (µmol/m2/second).
Objectives
The DLI and PPFD Data section of this blog provides greenhouse producers in southwestern Ontario with outdoor light levels on a regular basis year-round. It is meant to serve as a record of the amount of light this location received on a daily basis throughout the year.
Each blog post in this section contains tables with the available data for a one-month period and an Excel file with data from previous months.
NOTE: This data is provided for information purposes and does not represent the amount of light at other locations.
Materials and Methods
The data was collected using a DLI-600 sensor from Apogee Instruments. It measured the extended PAR (ePAR) spectrum (400-760 nm), which includes far red light. The sensor was placed 90 cm off the ground outside of a greenhouse near the Leamington-Kingsville border in Ontario.
A NanoLambda light meter was also used to measure irradiance (W/m2 for light in the 340-1010 nm spectrum range) and PPFD (µmol/m2/second for light in the 400-700 nm spectrum range) at a specific date and time. It was placed beside the Apogee light meter when measurements were taken.
Available DLI data is presented for each month in Figure 1 and Table 1, for each day (24 hr period) of the current month in Figure 2 and Table 2, and it is all available to download in the attached Excel sheet in the last section.
DLI Data
Figure 1: Monthly DLI data for Leamington-Kingsville.
Table 1: Monthly DLI data for Leamington-Kingsville.
| Month and Year (number of days of data) | DLI (mol/m2/day) (average ± standard deviation) |
| July, 2025 (9 days) | 60 (± 14) |
| June, 2025 (29 days) | 53 (± 17) |
| May, 2025 (30 days) | 46 (± 20) |
| April, 2025 (29 days) | 43 (± 17) |
| March, 2025 (30 days) | 33 (± 12) |
| February, 2025 (28 days) | 21 (± 10) |
| January, 2025 (15 days) | 19 (± 5) |
| December, 2024 (0 days) | not available |
| November, 2024 (8 days) | 10 (± 5) |
| October, 2024 (13 days) | 34 (± 10) |
| September, 2024 (29 days) | 39 (± 14) |
| August, 2024 (27 days) | 49 (± 12) |
| July, 2024 (25 days) | 56 (± 12) |
| June, 2024 (22 days) | 59 (± 12) |
Figure 2: Daily (24 hr period) DLI data for Leamington-Kingsville for July, 2025.
Table 2: Daily (24 hr period) DLI data for Leamington-Kingsville for July, 2025.
| Date (day/month/year) | DLI (mol/m2/day) |
| 01-Jul-25 | 54.3 |
| 02-Jul-25 | 72.8 |
| 03-Jul-25 | 64.3 |
| 04-Jul-25 | 68.8 |
| 05-Jul-25 | 71.9 |
| 06-Jul-25 | 71 |
| 07-Jul-25 | 36.4 |
| 08-Jul-25 | 65.2 |
| 09-Jul-25 | 38.3 |
| July, 2025 DLI average ± standard deviation | 60 (± 14) |