Latest research: optimizing lighting for greenhouse cultivation

Photos courtesy of Resource Innovation Institute (RII)

The Resource Innovation Institute (RII) has gathered members of our Technical Advisory Council into Working Groups to develop best practices guides for controlled environment agriculture since 2019, when we published our Lighting Best Practices Guide for Cannabis Cultivation. The Key Horticultural Lighting Terms companion to the Lighting Guide helps growers and project teams use a common language to design systems for cultivation operations. Learn more on the RII catalog at bit.ly/usda-rii

Designing supplemental lighting systems

Along with facility type and crop type, the stages of plant growth that occur in greenhouses can influence the lighting equipment used for production.

There are various kinds of horticultural lighting systems used by CEA producers such as fluorescent lights like T8, high-intensity discharge (HID) lights like high-pressure sodium (HPS), and light-emitting diode (LED) fixtures. LED horticultural lighting products fall into two major categories: narrow band and full spectrum. Narrow band LEDs provide photons in a selection of wavelengths and often have a higher proportion of red diodes, increasing fixture PPE. Full spectrum LED fixtures produce photons from most wavelengths and often have a higher proportion of white or blue diodes, reducing fixture PPE.

In California, greenhouses installing new lighting systems or facilities replacing more than 10% of existing lights will need to comply with horticultural lighting minimum efficacy requirements when energy code changes come into effect at the beginning of 2023.

Greenhouses with more than 40 kW of connected lighting load must use light fixtures with PPE of at least 1.7 µmol/J. This can be achieved with double-ended HPS fixtures and LED solutions. In the future, code minimum PPE may be raised to mandate LED horticultural luminaires.

Prepare for regulations and maximize energy efficiency in greenhouses by using certified lighting equipment. Independent organizations can help you select equipment certified to meet minimum technical requirements set by subject matter experts. The DesignLights Consortium (DLC) is a nonprofit organization that qualifies the performance of high-performance lighting technology like horticultural LED light fixtures and lamps. Look for the DLC logo when reviewing product specification sheets (see figure at right). Growers who may not trust LED fixtures can find peace of mind in the third-party assurance of quality that DLC qualification can provide.

The DLC develops technical requirements for horticultural lighting products and qualifies equipment to be included in their Horticultural Qualified Products List (Hort QPL). Fixtures listed on the Hort QPL must meet equipment testing and reporting, and thresholds for minimum photosynthetic photon efficacy (PPE), flux maintenance, component lifetime and warranties. All manufacturers must submit their products to be tested by a third-party laboratory to be considered for qualification. Performance and lifetime claims are evaluated through third party LM-79, ISTMT and safety testing reports.

Products that meet the required performance criteria can be added to the QPL. The Hort QPL offers programs and cultivators over 550 fixtures that meet the criteria outlined in the DLC Horticultural Technical Requirements V2.1. The DLC will be issuing a draft for V3 of the Horticultural Technical Requirements later in 2022. The timeline for when V3 would come into effect is still being determined. An efficacy increase is being considered. Efficiency programs may use the Hort QPL of LED lighting systems when specifying eligible equipment for their CEA programs. The Hort QPL is available online at designlights.org/qpl/hort.

Efficiency programs in 35 states support efficient horticultural lighting equipment, and 275 programs in regions across the nation offer specialized horticultural lighting incentives.

The average rebate for a 600 W LED fixture replacing a 1,000 HPS fixture is approximately $160 in February 2022. Contact programs early in design to understand requirements for incentives and understand how high-performance fixtures with high PPE can receive custom financial support. Efficiency programs may use the DLC Hort QPL of LED lighting systems when specifying eligible equipment for their CEA incentive programs. Do not assume that a DLC-listed fixture automatically qualifies for rebates and check with your efficiency program partner before purchasing any equipment.

Share lighting design details with utilities and efficiency programs so they can calculate your facility’s energy savings and custom financial incentive. In some regions, growers can receive rebates for horticultural lighting through rebate programs that do not require energy modeling.

Benchmarking lighting system operation

In 2020, RII and ACEEE were awarded a Natural Resources Conservation Service Conservation Innovation Grant from the United States Department of Agriculture (USDA) for a project titled Data-driven market transformation for controlled environment agriculture.

In 2021, RII began to benchmark food and floriculture greenhouses and indoor farms with PowerScore to help producers identify efficiency opportunities and celebrate energy and water best practices.

One of the early participants in the benchmarking initiative is the University of Vermont’s (UVM) Stafford Greenhouse, the main academic greenhouse serving the campus for research, teaching and production activities. The facility has benchmarked two years of energy performance, space utilization and revenue in order to measure the impact of 36 new horticultural light fixtures installed in 2021.

In addition to 18 new double-ended HPS light fixtures, 18 new DLC-listed LED fixtures were also purchased thanks to funding received from a UVM Core Facility Upgrade Fund grant. For each LED fixture, UVM received a rebate of $150 from their local efficiency program, the Burlington Electric Department, for a total rebate savings of $2,700.

Benefits of LED lighting

The University of Vermont is committed to using electricity efficiently and reducing energy consumption, and although lighting at the Stafford Greenhouse is a small energy consumer in comparison to the wider university campus, greenhouse growers will know that supplemental lighting costs make up a significant portion of their expenditures.

When the need arose to upgrade lighting at the facility, we knew it was the perfect opportunity for the greenhouse to invest in a high-quality lighting system befitting an academic research and teaching institution, while also making strong strides toward the UVM sustainability commitment.

The LED lighting investment is paying off, and already the Stafford Greenhouse is seeing a reduction in electrical consumption and an increase in overall research space use. The installation of LED fixtures at the Stafford Greenhouse last year has resulted in a savings of 9% total electricity use from greenhouse lighting system operation, and from the electrical savings alone, the greenhouse is on target for a simple payback of less than five years.

In addition to energy savings, the installation of all new supplemental lighting in 2021 increased facility space use by 6% between 2021 and 2022, allowing for more research, teaching and production activities. In turn, this has increased the dollar value of space in use by 17%, so that in 2022, the value of space in use is now more than double the cost of annual lighting system operation.

The academic greenhouse has over 50 1,000-Watt HPS fixtures each still in use, which drive peak demand charges on their utility bills. RII evaluated the electrical energy and demand savings from replacing the remaining HID light fixtures with LED would reduce electricity use by 24% and drop annual electric bills by over $9,000 (including peak demand savings of $4,000 per year). Including efficiency program rebates, the LED fixture replacement would pay back within five years.

The Stafford Greenhouse is located in Vermont, which has the ninth highest electricity costs in the United States. If costs of energy continue to rise, the return on investment for LED replacements will become shorter. Many greenhouses can use LEDs to support research and production activities while also providing cost-effective payback periods. In all scenarios modeled by RII, staged or comprehensive, the payback period for DLC-listed LED horticultural lighting was less than seven years.

About the authors:
As technical & operations director of RII, Gretchen Schimelpfenig manages the PowerScore resource benchmarking platform, facilitates RII’s Technical Advisory Council Working Groups and creates curriculum and training to educate producers, efficiency programs, and design and construction communities. She works with members and subject matter experts to publish best practices guidance for production of plants in controlled environments, develops and delivers curriculum, and supports PowerScore users with resource benchmarking analysis and reporting compliance. Gretchen grows vine crops and herbs in her veggie garden, greenhouse and basement in her Vermont farmhouse. Derek Allen is the greenhouse facilities director at the University of Vermont.