Using a High Yield Photoperiod to Increase
Lettuce Production by 40%

Introduction

Daily Light Integral (DLI) is a commonly used metric to describe the amount of light a plant receives in a day. It is well-established that an increase in DLI generally correlates with an increase in crop growth, quality, and yield. LumiGrow Research investigated the effects of differing day lengths and intensities with equal DLI to better understand how to use supplemental lighting efficiently for growing leafy green crops. LumiGrow Research found that extending the photoperiod while maintaining the same DLI increased the harvestable biomass of baby lettuce by over 40%, and of mature lettuce by 15% in a greenhouse production environment.

The breakthrough discovery by LumiGrow Research is now being termed as a “High Yield Photoperiod”. “High Yield Photoperiod” lighting strategies dramatically boost crop yields by utilizing the same amount of energy that your lighting system is already using and delivering this light more appropriately over a longer period of time throughout the day. The process of maintaining a consistent DLI over a longer photoperiod has only recently become commercially feasible with the technological advancement of the world’s first integrated horticultural light sensor. The LumiGrow Light Sensor works with the LumiGrow smartPAR software platform by taking in solar data and using predictive analytics to automatically adjust LumiGrow fixtures. This makes it possible to achieve a specific DLI and photoperiod in a precise and consistent manner. In past studies, LumiGrow Research found that peppers and tomato seedlings grown under longer photoperiods with a similar DLI produce more overall growth. This research demonstrates the profound potential for achieving a “High Yield Photoperiod” for many types of crops.

Materials and Methodology

Methodology

Skyphos lettuce was grown under LumiGrow Pro 325 fixtures in a double-poly hoop house production environment at Cabrillo College in Aptos, CA. Seedlings were germinated and grown in a propagation area until first true leaves formed, then placed into treatments. Plants were grown for approximately 4 weeks under treatment conditions before destructive measurements were taken. Fresh mass and dry mass measurements were taken. Two replicates were conducted, reversing the placement of the two lighting conditions in the greenhouse.

Plant Materials

Light Conditions

Results

Lettuce Biomass Comparison

The combined data from both replicates demonstrated a fresh biomass increase of over 40% in baby lettuce, and a 15% increase in mature lettuce after a full production cycle is possible with longer photoperiods while maintaining a consistent DLI. The data for respective conditions was similar between replicates. Additionally, both replicates demonstrated a dry weight increase that correlated with the increase in fresh biomass. This demonstrates that the increase in fresh weight was due to increased production of leaf tissue.

Tip Burn Comparison

Skyphos in the 12-hour photoperiod exhibited greater tip burn in comparison to the 21-Hour treatment. This suggests photoperiod may allow for management of controlled environment production issues.

Conclusion

Smart LED lighting can be used to consistently achieve a higher DLI and longer photoperiod than solar light alone in the greenhouse. When maintaining a DLI of 17 mol-m^-2-day^-1, overall increases in fresh weight biomass under 21-Hour treatments compared to 12-Hour treatments can exceed 40% in baby lettuce and 15% in mature heads of lettuce. This methodology uses the same overall power usage to drive increased productivity.

Research conduct by:
Jake Holley, Brian Poel, Sarah Hulick, Peter Shaw, and Melanie Yelton
LumiGrow, 1480 64th Street, Emeryville, CA, 94608, USA.
Cabrillo College, 6500 Soquel Drive, Aptos, CA 95003, USA