LED Lighting for Indoor Agriculture

Len Calderone for | AgritechTomorrow

01/10/19, 08:14 AM

Since the beginning of time, plants have relied on the sun to feed and grow through the method known as photosynthesis—a process used by plants and other organisms to convert light energy into chemical energy. Now, plants can be commercially grown without any sun light. LED lighting is replacing the sun due to advanced technological innovations.

Light emitting diodes (LED) work by passing a current between semiconductors. Compared with other forms of electrical illumination, LEDs use less energy, give off little heat and can be controlled to optimize plant growth compared to other forms of electrical illumination, such as fluorescent lamps, which contain mercury, which is needed to make the inert gasses conductive at all temperatures and to make the lamp work properly and efficiently. Mercury is a heavy metal, which is hazardous to the environment.

Then, we have incandescent lamps that are considered the least energy efficient type of electric lighting commonly found in residential buildings. Because of their inefficiency and brief life spans, they are more expensive to operate than LED and fluorescent lights.

LEDs are tiny light bulbs that fit into an electrical circuit. Unlike incandescent bulbs, they don't have a filament that will burn out, and they don't get very hot. They are illuminated uniquely by the movement of electrons in a semiconductor material. The lifespan of an LED exceeds the short lifespan of an incandescent bulb by thousands of hours.

In LEDs, the conductor material is usually aluminum-gallium-arsenide. In pure aluminum-gallium-arsenide, all of the atoms adhere entirely to their neighbors, leaving no free electrons to conduct electric current. Additional atoms change the balance by adding free electrons or creating holes where electrons can go. Either of these variations make the material more conductive.

In agricultural applications, LED lights are used to change how plants grow, alter when they flower, transform how they taste and even modify their levels of vitamins and antioxidants. LED lights can extend a plant’s shelf life as well.

Growers can use LED light modifications to grow two types of basil from the same plant.  For example, they can grow sweeter basil for the grocery store and more spicy versions for chefs.

These plants are grown indoors, utilizing a fraction of the land, water and fertilizers of greens raised outdoors with conventional farming. Since the plants are gown indoors, they can be grown close to urban centers. Growers don’t need varieties bred for disease resistance, or plants genetically modified to handle the stresses of growing outside. The harvest isn’t transported across the country in refrigerated trucks, and they are not susceptible to the effects of climate change, which is making growing much more difficult for a lot of farms around the country and around the world.

Indoor growing and LEDs allow fast, year-round crop cycles. This permits growers to produce 200,000 pounds of leafy greens, vine crops, herbs and microgreens annually in a 12,000-square-foot warehouse, which is the equivalent of 80 acres of farmland. Not dependent on the outside weather, plants can grow year-round, enabling a grower to produce 15 or more crops a year.

Conventional greenhouses have depended on on high-pressure sodium lamps (HPS) to complement sunlight, but HPS lights don’t work as well as LED because they consume much more power to produce the same light levels. They also generate too much heat to place near young greens. Greenhouses are moving to a combination of HPS and LED lighting for supplemental lighting, though growers see a time when they will use LEDs alone. Lately, LED lighting costs have been cut in half, and their effectiveness has more than doubled.

Scientists have acknowledged that photosynthesis is improved within the red band, but plants also need blue light waves to prevent stretching and enhance leaf color. A visible range beyond red, known as far red, encourages larger leaves, branching and flowering. With advances in LED technology, light recipes can be finely tweaked to each crop and even to each phase in a crop’s life.

Sunlight is inefficient when it comes to improving small-scale, urban agriculture. The heat produced by the sun can damage plants. The sunlight’s heat effect is further amplified when the plants are packed close together, which they are in urban farming.

In contrast to sunlight, LED lights are known for shifting nearly undetectable amounts of heat onto plants, and the light bulbs are cool to the touch. When using LED lighting, urban farms can closely pack plants for maximum efficiency. This would not be achievable in ordinary agricultural environments without conceding the health of the plants.

There is normally a higher upfront cost using LED lighting. The best way to acknowledge the cost-savings of LED lighting is to look at it in terms of a long-term investment. Over time, LED lighting has a much higher energy productivity over time as compared to other urban farming lighting technologies.

LED's use much less electricity than pressure sodium lights or fluorescent, as much as 40% - 50%. For indoor growing, proper ventilation is required. Ventilation for indoor growing helps prevent excess moisture, the propagation of pests and the weakening of plant stems. LEDs produce much less heat than other types of grow lights, resulting in the need for less ventilation.

LED's grow lights have an extreme life length. They typically have 50,000 hours of usable life, which is approximately 6 years of continuous use. So, if you are utilizing the lights on a 50% on 50% off schedule, the life of LED grow lights is over 11 years.

Since LED's have much lower heat output, they can be located nearer to the plants. This allows the grower to stack more plants in the same vertical space. Therefore, the benefit of using LEDs is to double or triple the production output without changing the area of the growing space. Of course, this depends on the height of the growing space.

As used in commercial indoor growing, LED lighting technologies have been around less than ten years. LED lights are less understood than other types of grow lights, which have been studied for several decades. So, what does this mean? The support for and the knowledge of LED grow lights is far more limited than other types of grow lights. Most importantly, because of the knowledge gap, there are great opportunities.