Summary
Leamington-Kingsville and Vineland received approximately 1/3 less light in December than November.
The average DLI for the month of December, 2025 for Leamington/Kingsville was 10 moles/m2/day. The maximum DLI was 18.1 recorded on December 4th, and the minimum DLI was 2 recorded on December 26th.
The average DLI for the month of December, 2025 for Vineland was 7.9 moles/m2/day. The maximum DLI was 14.7 recorded on December 5th, and the minimum DLI was 1.8 recorded on December 26th.
Listen to the monthly DLI radio report (below) that airs on the second Tuesday of every month on Country 92.9 during the agriculture show at noon.
Background
We mounted a daily light integral (DLI) meter on the border of Leamington and Kingsville, Ontario, in 2024, and another DLI meter at the Vineland Research and Innovation Centre (VRIC) in Vineland, Ontario, in 2025 to give greenhouse producers in those areas access to readily available light data.
The details of the Leamington-Kingsville data is available on this blog. If you are interested in the VRIC data, you can download the excel sheet at the bottom of this post or visit the ONFloriculture blog for more details.
Daily light integral (DLI) and photosynthetic photon flux density (PPFD) data are 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).
The data provided here reflects the amount of outdoor light. The amount of light that greenhouse crops receive inside a greenhouse can be significantly lower (90-50%) and is affected by the cover material (clear glass, diffused glass, single polyethylene, double polyethylene, triple polyethylene, etc.), cover material treatment (whitewash), and curtains (shade, energy, blackout, etc.). The ideal DLI inside a greenhouse for each crop is different. You can find more information on DLI levels for greenhouse fruit and vegetable crops in the production guides available in the OMAFA Greenhouse Fruit and Vegetable Publications section of this blog.
Objectives
The DLI and PPFD Data section of this blog provides greenhouse producers in southwestern Ontario and Niagara Region with outdoor light levels on a regular basis year-round. It is meant to serve as a record of the amount of light these locations 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 DLI-600 sensors from Apogee Instruments. They measured the extended PAR (ePAR) spectrum (400-760 nm), which includes far red light. The sensors were placed 90 cm off the ground outside of a greenhouse near the Leamington-Kingsville border and at VRIC in Vineland, Ontario.
When possible, 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: Available monthly DLI data for Leamington-Kingsville and Vineland in 2024 and 2025 presented in two graphs. A) Bar graph representing average ± standard deviation, and B) box whisker graph representing the average (indicated by the x within the box), median (indicated by the horizontal dash within the box), 25-75% of the data (indicated by the box) and minimum and maximum values (indicated by the ends of the whiskers or outlier values above and below the box).
A)
B)
Table 1: 2025 Monthly DLI data for Leamington-Kingsville.
| Month | Number of Days of Data | Monthly Average DLI (mol/m2/day) (average ± standard deviation) | Monthly Maximum DLI (mol/m2/day) | Monthly Minimum DLI (mol/m2/day) |
| January | 15 | 19 (± 5) | 28.4 | 8.7 |
| February | 28 | 21 (± 10) | 39.2 | 5.9 |
| March | 30 | 33 (± 12) | 50.1 | 9.8 |
| April | 29 | 43 (± 17) | 67 | 6.1 |
| May | 30 | 46 (± 20) | 72.9 | 9.3 |
| June | 29 | 53 (± 17) | 74.7 | 12.5 |
| July | 9 | 60 (± 14) | 72.8 | 36.4 |
| August | 24 | 50 (± 15) | 63.8 | 11.4 |
| September | 29 | 44 (± 11) | 59.6 | 13.5 |
| October | 30 | 30 (± 11) | 42.8 | 6.7 |
| November | 29 | 15 (± 9) | 30.5 | 3.3 |
| December | 30 | 10 (± 5) | 18.1 | 2 |
Figure 2: December, 2025, daily (24 hr period) DLI data for Leamington-Kingsville.
Table 2: December, 2025, daily (24 hr period) DLI data for Leamington-Kingsville.
| Date (day/month/year) | DLI (mol/m2/day) |
| 01-Dec-25 | 14.4 |
| 03-Dec-25 | 6.8 |
| 04-Dec-25 | 18.1 |
| 05-Dec-25 | 17.1 |
| 06-Dec-25 | 7.9 |
| 07-Dec-25 | 9.8 |
| 08-Dec-25 | 16.7 |
| 09-Dec-25 | 6.6 |
| 10-Dec-25 | 3.3 |
| 11-Dec-25 | 9.6 |
| 12-Dec-25 | 14.2 |
| 13-Dec-25 | 6.1 |
| 14-Dec-25 | 12.2 |
| 15-Dec-25 | 8.9 |
| 16-Dec-25 | 15.3 |
| 17-Dec-25 | 14.3 |
| 18-Dec-25 | 10.9 |
| 19-Dec-25 | 5.2 |
| 20-Dec-25 | 8.2 |
| 21-Dec-25 | 15.7 |
| 22-Dec-25 | 6.2 |
| 23-Dec-25 | 12.6 |
| 24-Dec-25 | 13.9 |
| 25-Dec-25 | 12.9 |
| 26-Dec-25 | 2 |
| 27-Dec-25 | 6.4 |
| 28-Dec-25 | 2.1 |
| 29-Dec-25 | 7.9 |
| 30-Dec-25 | 11.9 |
| 31-Dec-25 | 4.8 |
| December, 2025 DLI average ± standard deviation | 10 (± 5) |