Understanding PAR, PPFD, and DLI in Cannabis Cultivation

When cultivating cannabis, especially indoors, light plays a crucial role in yield and quality. Here, we’ll explore three essential terms—Photosynthetically Active Radiation (PAR), Photosynthetic Photon Flux Density (PPFD), and Daily Light Integral (DLI)—and how they relate to maximizing cannabis growth and potency.

What is PAR?

Photosynthetically Active Radiation (PAR) refers to the range of light wavelengths (400-700 nm) that plants use for photosynthesis. PAR doesn’t measure light quantity but rather identifies the light spectrum that supports plant growth. It covers the colors from blue to red, which are essential for cannabis because they influence different growth stages. Blue light, for example, promotes vegetative growth, while red light supports flowering and bud development.

Understanding PPFD

Photosynthetic Photon Flux Density (PPFD) measures the intensity of PAR light that hits a specific area (typically measured in micromoles per square meter per second, or µmol/m²/s). In simple terms, it’s the amount of usable light reaching the plant. Higher PPFD values generally support faster growth but should be matched to the plant’s tolerance level to prevent light stress.

For cannabis, target PPFD values vary by growth stage:

• Seedling Stage: 100-300 µmol/m²/s
• Vegetative Stage: 400-600 µmol/m²/s
• Flowering Stage: 600-900 µmol/m²/s

Higher PPFD during the flowering stage can improve bud density and yield but requires careful monitoring to prevent overheating and ensure plants can absorb the light provided.

The Role of DLI in Cannabis Cultivation

Daily Light Integral (DLI) represents the total amount of PAR light a plant receives in a day, calculated in mol/m²/day. It factors in both light intensity (PPFD) and the duration of exposure. For cannabis, DLI requirements vary depending on whether the plant is photoperiod or autoflowering.

• Photoperiod Strains: These strains depend on light cycles (typically 18/6 for vegetative and 12/12 for flowering). During the vegetative phase, cannabis may benefit from a DLI of around 25-30 mol/m²/day. During flowering, this can range between 20-25 mol/m²/day due to the shorter daylight period.
• Autoflowering Strains: Autos are not dependent on light cycles, often receiving continuous light (18-24 hours) throughout their lifecycle. For autoflowers, DLI can range higher, with 35-40 mol/m²/day being optimal, as the constant light allows for rapid growth and development.

How PAR, PPFD, and DLI Affect Yield and Quality

Achieving the right balance of PPFD and DLI directly impacts cannabis yield and quality. Over-lighting can lead to bleaching, heat stress, and nutrient burn, while under-lighting reduces yields and quality. Matching DLI and PPFD to the specific growth phase and plant type promotes better photosynthesis, increases THC and terpene production, and supports denser, larger buds.

In conclusion, understanding and optimizing PAR, PPFD, and DLI helps growers provide their cannabis plants with ideal light conditions. Monitoring these parameters can be the difference between an average and a high-quality harvest, making them fundamental for anyone looking to optimize cannabis cultivation.

How to Measure PPFD, PAR, and DLI with Photone

Measuring PPFD (Photosynthetic Photon Flux Density):

1. Download the Photone app on your smartphone and calibrate it. You will need either a filter purchased from Photone, or you can use a sheet of white paper 80 g/m2 or 22lb.
2. Position your phone’s sensor directly under the light source at canopy level.
3. Record the PPFD value displayed in micromoles per square meter per second (µmol/m²/s).

Measuring PAR (Photosynthetically Active Radiation): PAR is the light spectrum usable by plants (400-700 nm). Photone automatically filters light to this range, giving you PPFD directly related to PAR.