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Growing Indoor Plants Using LED Lighting

(An abridged version is found in the SEPTEMBER 2010 issue of Maximum Yield.)

If You Can't Stand the Heat…

Growing Indoor Plants Using LED Lighting
By Brian Chiang and Josh Puckett

LED lighting is a rapidly changing field that is sparking excitement everywhere, from general lighting to entertainment lighting to horticultural lighting! With their energy saving features, long lifetimes, and no toxicity, LEDs are beginning to become prominent in the indoor growing world.

The advent of densely packed, high intensity, horticultural LED technology is giving indoor growers opportunities that were not previously available. As LED technology allows for the isolation and mixing of wavelengths, growers can now control the wavelength combinations and lighting regiments that they administer to their plants. Due to the low heat output of LEDs, growers can now increase light intensity by closing the distance between lights and plants. The design and size of emerging LEDs has improved their versatility from large broadband lights, such as metal halide (MH) or high pressure sodium (HPS) lights.

LED technology is forcing the horticultural lighting industry to reexamine the way temperature, ventilation, circulation, CO2, humidity, watering, and fertilizer are managed.The prevalence of broadband sources like large, high wattage high intensity discharge (HID) systems has dictated the way indoor growers perceive the indoor growing space and management of indoor crops. The complications typical of these lighting systems have been accepted as standard procedure and are often not considered in the comparison of LED with conventional systems. However, there are vast differences to be addressed when comparing these two types of lighting systems. LEDs emit so little heat especially in contrast with broadband sources that many of the equipment required for indoor growing with broadband lights will be rendered useless. This will allow growers to save on costs, time, and effort as they transition to LEDs.

LEDs are turning up the heat on broadband sources — ironically because they produce so little heat!

Temperature and Ventilation

One of the biggest differences between LEDs and broadband light sources is how efficient each light is at converting energy to light. Broadband sources are notorious for the excessive amount of heat produced when converting energy to light. This is a problem as temperature control is extremely important when growing indoors. The temperature of the growing space must be at a level that is comfortable for the plants. Excessive heat can cause water to evaporate and plants to dry out. It can also give plants unnecessary stress, leading to vegetative damage, flower sterility amongst crops, decreased flower and fruit production, and ultimately a reduction in crop yield.

As a result, most broadband sources have to work in conjunction with an expensive venting system. Intricate ventilation and circulation systems, with multiple controllers and fans help to remove a fraction of the heat in grow rooms or airtight tents. One fan is kept in the lighting fixture itself, while another is situated to the side to pump heated air out. This separate system is installed in the growing area to help direct heat away from the plants into the outside environment. During the summertime when the weather is significantly hotter, air conditioning is often required to lower and steady temperature levels. Good ventilation is necessary for control over the temperature in the contained area to monitor the stability of the growing environment.

With LEDs, there is no need for a separate venting system. Because they are efficient at energy conversion to light, LEDs are naturally cool. This is a big advantage for growers as it eliminates another aspect that they have to otherwise monitor. Growers don't have to worry about the temperature getting too hot in the growing area and inhibiting the growth of their plants.

CO2 and Circulation

Carbon dixode (CO2) is an important ingredient in allowing photosynthesis to be carried out in plants. Plants turn the carbon into energy for food, and release oxygen as a byproduct. Knowing this, growers often provide plants with supplemental CO2 when planting in an enclosed space.

In a contained growing area, two fans are usually already present in the venting system provided to broadband light sources. To help increase circulation at the plant level, another fan is often situated near the plants. This helps to provide enough air circulation around the plants and monitor the heat that isn't directly taken out by the venting system. However, this extra movement in the air also takes out useful CO2, making it harder for plants to utilize the supplemental CO2 growers may allot to plants.



When using LED sources in a contained area, circulation is still a recommended practice. The circulation fan can be used at lower speeds or more sporadically under LED lights to give just a little bit of helpful stress to plants and keep them strong. However, since ventilation fans aren't required, less air is vented out of the growing environment to allow plants to better utilize supplemental CO2.

Most of these parameters don't apply when growing in an open area, since there is more ventilation; however, a small fan may be used to increase circulation if needed.

Humidity, Watering, and Nutritional Additives

It is possible to maintain the same temperature levels between broadband sources and LEDs. It is not quite so easy to monitor humidity levels. The high temperature associated with broadband lights decreases humidity levels and leads to increased rates of evaporation and evapotranspiration in plants. In high temperatures, the kinetic energy of each water molecule is raised. The water molecules move faster, allowing them to evaporate from the plants more easily. Water molecules in the air can hold heat, absorbing the kinetic energy from the radiated light and making them more susceptible to escaping the contained area. Water and the nutritional additives in the water in hydroponics growing are then also directed away from the plant, hindering their growth.

To compensate the loss of water, growers using broadband sources must then increase the number of times they water and the amount of nutritional additives allotted to plants. This is true for hydroponics systems as well. Water and nutritional additives in the water must be changed and added more frequently, because of the high evaporation rates under broadband light sources.

On the other hand, LEDs emit much less heat, making it much easier to control humidity levels within an enclosed growing area. Less heat lowers the kinetic energy of the air and water molecules so that they move slower to stay in the contained area. Water molecules are unable to escape as quickly. This leads to a more stable humidity level, which means less frequent watering. For hydroponics systems, this lowers the rate that growers have to change water or add nutrients to the water.

Light Intensity

Photosynthesis is the process plants use to convert light into food. The intensity of the light provided to plants plays a large role in photosynthesis. Photosynthesis occurs in the leaves of the plants in structures called chloroplasts that contain chlorophyll. Chlorophyll serves to harvest the light photons that are then passed on from molecule to molecule until trapped by photosynthetic reaction centers located deep within the chloroplast. These reaction centers then take the light energy to use in the photosynthetic process.

A reaction center intercepts only around one photon every second, so the chlorophyll's ability to capture light is critical. The more photons, the more chances the chlorophyll will have to transfer the photons to a reaction center. This is where light intensity becomes an issue. A more intense light means that more photons are being emitted. With more photons, the probability that a photon will reach a reaction center is much higher. Take a simple ring toss for example. The more rings you have to throw, the higher the chances are that you will hit a target bottle. In the same way, plants benefit from having higher light intensity because a higher concentration of photons results in higher photosynthetic productivity.

However, the heat emitted by broadband sources (conventional HID lights) has long limited the amount of light supplied to plants. If the lights are placed too close to the grow area, the plants will burn from convection or radiation. Their large size also cuts the number of light fixtures that can be placed over a given grow area.

This is not an issue for LEDs. Because LEDs are a naturally cool light that efficiently converts electricity to light, growers will be able to place more LEDs over their plants to give that extra boost of light without having to worry about heat. Their small size also allows them to be used with more versatility in terms of special placements or larger numbers. With more light providing more photons for better photosynthesis, growers can expect a boost in performance from their plants. As LED technology continues to advance, growers will also begin to see smaller, brighter, more powerful LED products for their plants.

Spectrum

Plants respond favorably to specific wavelengths in a light spectrum. However, broadband systems present the commonly accepted defect of emitting a limited spectrum. The light that these systems produce is unbalanced. Wavelengths of light that are useless to plants are emitted from these systems, limiting their efficiency. Much of this extra light results in more heat, which is not beneficial to plant growth. As detailed above, getting rid of the excess heat requires complex engineering and expensive systems to be implemented.

In contrast, LEDs have the ability to produce wavelength specific light. This is the biggest advantage of LEDs in the indoor growing market. Because each LED emits a specific wavelength, growers can now optimize lights for plant growth. By mixing various LED chips, a complex light spectrum can be created as unique formulas for different growth conditions. Although we know that plants benefit mostly from the blue and red parts of the spectrum, making the best light is not as simple as using random blue and red LED chips. There are specific wavelengths that are ideal for plant growth. Different ratios of red and blue light will affect different types of chlorophyll (the main center of photosynthesis). Not only that, plants need different wavelengths during different phases of growth. For example, plants benefit from the red spectrum during the flowering phase.

Results will inevitably vary from crop to crop, and even strain to strain. As this is an active area of research, scientists are discovering more everyday not only which wavelengths benefit plants, but during what time of day or which growing phase to use them. Growers may even be able to limit their use of Plant Growth Regulators (PGR), since these special wavelengths would be optimized to produce similar results. Aside from cutting down costs, this gives the grower one less task to worry about. With more research, growers will better know which spectrums can accelerate or slow down growth, improve yields, or morph the shape of different plants.

Conclusion

There is still much to be discovered about this up and coming technology. As we accumulate more knowledge and LED technology overcomes the obstacles of increased intensity and optimal wavelength formulation, the indoor growing industry is presented with previously unavailable opportunities. The culture of indoor growing can now change for the better and accommodate the obligations that come with the promise of optimal and energy efficient indoor growing.

Energy-efficient, little heat produced, intense light, and spectrum specifying—these are just some of the advantages that are revolutionizing the way growers use light. LEDs will take the world by storm, bringing in a "Spectral Revolution" !

About the Authors

Brian Chiang is a seasoned veteran in the photonics industry. For the last 13 years, he has been with DiCon Fiberoptics, Inc., an advanced technology company based in California. Brian received his Bachelor's degree in physics from UC Berkeley and Master's degree in physics from UC Davis. He is currently the managing director for Kessil Lighting, a DiCon business division.

Josh Puckett graduated from Sonoma State University with a Bachelors degree in biology and an emphasis in plant biology and is currently working at the UC Davis Foundation Plant Services. He has years of hands on working experience in the horticulture and agriculture industries. He also serves as an advisor for the Kessil Research team.