What is DLI and why is it essential?

Growers need to balance multiple factors to ensure that their plants receive optimum lighting to achieve optimum growth and quality. One of these factors is the Daily Light Integral (DLI), a concept that has been used for several years now, but is becoming increasingly relevant in helping growers to refine their use of supplemental lighting.

DLI is measured by the total volume of photons of PAR that gather in a particular area of a set period of time. You can measure DLI using a variety of different tools, maps and systems – all designed to provide you with insight into what supplemental lighting methods or solutions you will need to optimise your grow lighting and light planning. There are numerous DLI maps available for the United States, South Africa, Canada, China and Europe, among others, and their value lies in their ability to help you refine your crop production outputs more efficiently.

DLI: The basics
DLI is, essentially, the volume of light that is photosynthetically active, the light that has a direct impact on plant growth, crop quality and yield. It has become an important tool for growers because DLI has to be managed as carefully as soil, nutrients and shade. DLI, by its nature, changes with the seasons, the time of year, the length of the day, and your latitude. Each of these factors influences the value of your DLI and what you should consider doing to improve it.

Ultimately, the reason why any grower uses supplemental lighting is to improve the quality of the light for the crops. The right lighting can have an immensely positive impact on the crop. As researchers in a study entitled ‘Measuring Daily Light Integral in a Greenhouse’ point out, the main reasons why growers focus on the correct lighting is because it can do so much more than just manipulate light levels. It can manage temperatures, minimise crop stress, and optimise photosynthesis. Which is where DLI comes in…

DLI: The importance
DLI has a major influence on plant growth, development, yield and quality because it ensures that the light received by the plants is optimum for their growth cycles and needs. It can have an impact on the growth of seedling roots and shoots, and it can impact the thickness of a plant’s stem or the number of flowers. According to the paper outlined above, ‘commercial growers who routinely monitor and record the DLI received by their crops can easily determine when they need supplemental lighting or retractable shade curtains’.

Let’s look at some numbers. DLI values in a greenhouse rarely rise above 25 mol.m2.d1, this is largely due to factors such as glazing, time and length of the day, cloud cover etc. Outdoor DLI values are between 5-30 mol.m2.d1 in the growing months but can drop to as low as 1-5 mol.m2.d1. With these numbers in place, you can use a reliable measurement tool that helps you to determine your DLI mol.m2.d1, and then you can use supplemental lighting to then optimise your DLI to match the specific requirements for crop, growth cycle and stage.