Summary
DLI data for the last two weeks of April were available for Leamington-Kingsville. Average DLI for the month of April, 2026 for Leamington-Kingsville was 43 moles/m2/day. The maximum DLI was 63.1 recorded on April 20th, and the minimum DLI was 14.8 recorded on April 29th.
The average DLI for the month of April for Vineland was 32 moles/m2/day. The maximum DLI was 56.5 recorded on April 22th, and the minimum DLI was 10.1 recorded on April 29th.
Leamington-Kingsville received 79% more light in April than March. The monthly DLI average for April, 2026 was similar to 2025, but the last week of April (week 17) received 22% less light in 2026 than 2025.
Vineland received 45% more light in April than March, but it received 26% less light than Leamington-Kingsville.
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 are available on this blog. If you are interested in the VRIC data, you can download the excel sheet at the bottom of this post.
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 is different for each crop. 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 at 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 week in Figure 2 and for each day (24 hr period) of the current month in Figure 3 and Table 2. 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, 2025 and 2026 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 and 2026 monthly DLI data for Leamington-Kingsville and Vineland. NA = not available.
Figure 2: Available weekly DLI data for Leamington-Kingsville and Vineland in 2024, 2025, and 2026. Week 1 = January 1-7, week 2 = January 8-14,…,week 52 = December 24-31.
Figure 3: April, 2026, daily (24 hr period) DLI data for Leamington-Kingsville.
Table 2: April, 2026, daily (24 hr period) DLI data for Leamington-Kingsville.
