According to Dr. Bruce Bugbee's research, cannabis can tolerate very high Daily Light Integral (DLI) levels, potentially as high as
60 to over 100 mol/m²/day, provided all other environmental factors (specifically
CO2, nutrients, and temperature) are optimized.
Key points from his research and discussions:
- High Tolerance: Dr. Bugbee has noted that cannabis can handle DLI levels up to and potentially exceeding the DLI found in natural full sunlight on a clear summer day (which can reach 60 mol/m²/day or more).
- Optimal Conditions are Key: Pushing to these extreme DLI levels is only effective if other conditions are perfectly dialed in. High light intensity in a poor environment (e.g., inadequate nutrients or CO2, incorrect temperature/VPD) can lead to stress or light burn.
- CO2 Enrichment: Dr. Bugbee emphasizes that CO2 enrichment (to around 1200 ppm) is crucial to leverage high light intensities and avoid diminishing returns or yield dilution.
- Diminishing Returns: For many home growers not supplementing CO2, a DLI near 40 mol/m²/day may be a practical point of diminishing returns before needing advanced environmental controls.
- Variations by Stage: While high DLI can be beneficial during mid-to-late flower, some growers, referencing his work, suggest slightly reducing DLI in very late flower to potentially avoid issues like "foxtailing" (a type of abnormal bud formation).
In summary, while cannabis can technically tolerateextremely high DLI under optimized, research-level conditions, a more common and achievable high DLI range for advanced growers is often considered to be around 45-60 mol/m²/day when using CO2 supplementation.