Daily light integral (DLI), represents the number of photosynthetically active photons that are delivered to a given space over the course of a day. Considering not all wavelengths of light can be utilized by plants, it’s important to distinguish between PAR light and visible light. PAR stands for photosynthetic active radiation and represents the area within the visible light spectrum that drives photosynthesis (400 – 700 nm). This range in the visible light spectrum is also known as the quantum response area. PAR light is typically measured as PPFD, photosynthetic photon flux density. PPFD measures the precise number of photons that are delivered to one square meter in a given second. Quantum sensors are used to measure PAR light. They help growers calculate the daily light integral, the most accurate measurement for horticultural lighting.
Factors that can affect DLI are geographic location, weather and season. These variables cannot be controlled in an outdoor environment. Indoor horticulture allows for control of these metrics and consistency throughout a grow cycle. Light, temperature and carbon dioxide concentrations are the three factors that affect the rate of photosynthesis. An increased rate of photosynthesis promotes root development, plant growth and overall biomass production.
Many studies have shown that dialing in DLI values for specific crops can lead to increased flower number, larger biomass and decreased growth cycles. Various crop species require different DLI values for optimal growth. Plants also require different DLI values during various points in their life cycle. For instance, fruits and vegetables require DLIs ranging from 14-40 mol m-2d-2. Meanwhile, cannabis requires a much higher DLI. Large cannabis plants need about 65 mol m-2d-2 during their flower cycle. Sea of green grown cannabis requires about 48 mol m-2d-2 during flower. The sea of green growing method focuses on cultivating a large quantity of small plants, typically grown in vertical racking systems. Traditionally, growers cultivated a small number of large plants.