The summer solstice, June 21st, is the day with the longest lighting hours for growers in the northern hemisphere. Many happy growers and happy plants bask in the long hours of free natural light, but for others, it is a reminder that times are not always this good. Starting June 22nd, the days begin to get shorter, and before no time, winter is coming.
No greenhouse grower of light loving crops is immune from the challenges that winter light levels pose for their crops. The graph below shows the total photosynthetically active radiation (PAR) light intensity on average per month for Carpinteria, CA. Although light levels are abundant during the summer months, even in Southern California the drop off in light levels is dramatic come fall.
Figure: Daily Light Integral (DLI) Estimates for the inside of a greenhouse in Carpinteria, CA
Additionally, increased weather extremes outside of historic norms can lead to additional challenges. For example, many Southern Californian greenhouse growers reported lower yield and quality during the past winter season due to the record rainfall accompanied by months of above average cloud coverage. But, regardless of crop type, customers for tomatoes, lettuce, cannabis, etc. all continue to demand high quality products that meet their demands year-round.
Figure: Supplemental LED Philips Toplight Linear lights deployed in a cannabis greenhouse
Supplemental LED lighting is the best solution to buffer against the impacts of upcoming low-light seasons. Depending on a growers situation, a well designed supplemental lighting solution can allow for light levels to meet or exceed target levels year-round, allowing for more consistent yield and quality metrics year round. How much light is provided is customized based on individual growers’ situation, crop, greenhouse dimensions and structure, and budget.
Figure: Daily Light Integral (DLI) Estimates for the inside of a greenhouse in Carpinteria, CA with the addition of supplemental LED lighting.
Implementation of lighting controls and dimmability allows growers to “flatten the curve”. More advanced control systems can integrate with the onsite environmental control solution to respond to real time changes in PAR light measurement inside the GH. Maintaining consistent light levels year-round by responding in real time to high and low light conditions allows growers to maximize production and/or reduce energy costs.
Figure: Daily Light Integral (DLI) Estimates for the inside of a greenhouse in Carpinteria, CA with the addition of supplemental LED lighting and lighting controls.
Once a location’s natural daily light integral inside the greenhouse is determined, a target supplemental DLI can be determined. Many different variables go into a lighting calculation such as a light’s output, spacing, form factor, beam angle, mounting height, crop height, etc,. But ultimately, dividing the Daily light integral (Mol/day) by lighting hours/photoperiod (hrs/day) determines the target supplemental light intensity (umol/s/m2). Implementing a supplemental lighting solution is the only way to keep yields near their summer levels, even when winter has arrived.