Developing LED Lighting Technologies and Practices

for Sustainable Specialty-Crop Production

 

Summary of Research Objectives

Background

Commercial specialty-crop growers in the United States want affordable, efficient electric lighting to supplement limited sunlight for greenhouse production. Unfortunately, energy costs of growing specialty crops in colder climates during the off-season have taken many aspects of horticultural production to warmer, sunnier climates with cheaper labor, often outside the U.S. However, concerns about increasing costs and environmental footprint of long-distance transport, have renewed interest in local production. Developing a cost-effective greenhouse lighting system will help solve the energy dilemma that prevents establishment of a sustainable specialty-crop industry in the northern U.S. The light-emitting diode (LED) is key to improving energy utilization for greenhouse lighting.

What is an LED and why use them?

Light-emitting diodes (LEDs) are solid state, robust, very long-lived lights.  They can also be designed to emit pure, selectable colors. What’s more, the efficiency of converting electricity to light is improving rapidly as the LED industry evolves, so LEDs are becoming more energy efficient all the time! Unlike traditional light sources used in greenhouses today, the relative ‘coolness’ of LED surfaces allows them to be placed close to or touching leaves without overheating or scorching them. Thus, much less electrical power is needed to achieve the same or better plant response than with traditional lighting systems. LEDs can be designed so the colors they emit match exactly the colors most efficiently used by plant photosynthesis thus improving overall energy efficiency and giving more plant response for less light used.

Why not other lighting technologies?

In the floriculture industry, incandescent lamps long have been used to light greenhouse crops at the end of the day or briefly during the night to time precisely when flowering will occur. While incandescent lamps work well for timing, they emit colors that may cause unwanted stem elongation, are electrically inefficient, short-lived, and are being phased out by the government. Compact fluorescent lamps have been tested as an incandescent lamp substitute, and while they are more electrically efficient and much longer-lived, they also lack the colors of light required for the desired flowering response of certain plant types and also have hazardous waste disposal issues.

In other industries, especially the propagation and transplant industry, high-intensity discharge lamps are commonly used where and when natural sunlight is limiting. High-intensity discharge lamps produce sufficient light intensities to support transplant establishment, but have many drawbacks.  Specifically, they are intensely hot and have a high electrical energy draw and also do not emit the desired color of light resulting in poor plant quality for some species.

General research objectives

Over this four-year project, our research team will examine all aspects of LED lighting, from sociological to economic, and will establish industry standards for their use. Overall project objectives include achieving significant reduction of electrical energy utilization for all forms of crop lighting using LEDs with equivalent or superior crop response to conventional lighting sources.

LEDs will be evaluated in greenhouse trials, either to replace traditional lighting or to begin using LED-based greenhouse lighting for the first time. Plant performance will be measured by assessing health and vigor of plants, success in promoting or preventing flowering of select ornamentals, and yield of selected vegetables. Experiments will include comparisons with traditional lighting technology and no electric lighting. Energy consumption by light sources will also be measured.