A New Breed of LED - Intensified Lighting for Indoor Growing
(An abridged version is found in the AUGUST 2010 issue of Maximum Yield.)
"The Spectral Revolution"
In the July issue of Maximum Yield, we had previously discussed in "LED Technology Paves the Way for a Spectral Revolution" how LEDs are positioned to transform the way lighting is used. Their ability to produce wavelength specific light is the biggest advantage of LEDs in the indoor growing market. Light is essential to plant growth because it is converted into food and nutrition. Just as scientists have developed nutritional additives for plants to aid in their growth, advancements in LED lighting are allowing scientists to develop spectrums for different growing conditions.
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. With more research, growers will better know which spectrums can accelerate or slow down growth, improve yields, or morph the shape of plants.
This is only the beginning of the revolution. Through the specific wavelengths they emit, LEDs are allowing growers to have new ways to manipulate plant growth.
Light Intensity Matters for Better Plant Growth
Photosynthesis is the process plants use to convert light into food. In addition to the spectrum of the light received by the plant, the intensity of the light also plays a large role in photosynthesis.
Photosynthesis usually occurs in the leaves of the plants. The green color of the leaves comes from chlorophyll, the pigment that absorbs red and blue light energy and reflects the green.Chlorophyll is found in the interior of the leaves in structures called chloroplasts. Light must pass through several layers before it can reach the chlorophyll. Even then, the chlorophyll only serves to harvest the light photons. The photon is passed on from molecule to molecule until it is 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.
The "More" Factor
Heat from broadband sources (conventional HID lights) has long limited the amount of light supplied to plants. Such light, including the sun, emits more of the light spectrum than what is required for photosynthesis. Much of this light gives off heat as a byproduct, which is crippling to plant performance if the temperature of the environment is elevated beyond what plants can tolerate. Artificial sunlight sources also create heat on their own, due to inefficiency in converting energy from electricity to light. If the lights are placed too close to the grow area, the plants will burn from convection or radiation.
This is not an issue for LEDs. The ability of LEDs to specify wavelengths eliminates the excess light that contributes to unwanted heat. 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.
So What's the Problem?
If this is the case, why haven't most growers moved on to LEDs? Simply put, current LED grow lights don't have enough light intensity for photosynthesis. Although LEDs have the capability to specify wavelengths, the way most LED lights are packaged is just not made for effective plant growth. These fixtures are built with an LED die placed in a reflective cavity, bonded to two electrical contacts, and then sealed by an epoxy or plastic lens. The LEDs are then assembled by sparsely populating single LED chips over sheet metal to be secured in a panel to hang over plants. The goal of this light is to provide a broad, widespread light for general illumination purposes, or to use as decorative color changing Christmas lights. However, this bulky packaging limits the amount of LEDs growers can place over their plants, especially when the fixture is almost as large than the grow area! If growers can't use more LED lights over the grow area, the light intensity issue of these LED fixtures has to be remedied.
General consensus is that LEDs do work, but the overall intensity of the light is not enough. LEDs cannot be used to grow tall plants, because of this shallow penetration. Leaves closer to the roots will wither over time. Most LED lights have to work in conjunction with T5 lights, or lower power HID lights in order to be effective.
A New Breed of LED
Now half a century after LEDs were first introduced, a new LED platform is finally here. A breakthrough in material science has produced a material that dissipates heat rapidly. When LED chips are placed on this material, it is able to draw heat away from the LEDs quickly and efficiently. This advancement enables LED dies to be placed in close proximity to form a dense "matrix LED" platform. For example, this platform can populate more than 20 LED chips in an area no greater than a dime! What results is a very directional light that focuses on a much smaller area through an expertly designed reflector. This compact LED provides cool but intense light through this reflector for more photons. In addition, growers can place multiple of these lights over their plants. With more light that provides more photons for better photosynthesis, growers can expect a boost in performance from their plants.
The difference in the two packaging approaches for LEDs is seen in this simple illustration. The picture demonstrates an analogy using two different nozzles mounted on the same garden hose. On the left, water sprinkles out of many tiny pores from the sunflower-type nozzle. In contrast, the picture on the right shows a single jet of water from an industrial pistol nozzle. The sprayer on the left merely mists the surface of the plants while the steady stream on the right cuts straight down to the soil. Although the amount of water is the same for both hose heads, the nozzle from the right picture is drastically more effective in reaching plant roots.
Let's apply the garden hose example to understand how LEDs can produce much better results. Imagine the water as light. The typical LED light has tiny chips spread over a wide area similar to the individual holes that water trickles through on the left picture with the sunflower nozzle, and puts out equally weak light. Conversely, imagine if the light has many LED chips densely grouped together to send out an intense beam that behaves like the jet stream shooting out of the pistol nozzle in the right picture. Instead of sprinkling misty light onto the plant's surface layer, you would be able to inject light straight down to allow photosynthesis to also happen in the plant's lower tiers. With more of these lights over a grow area, all parts of the plants will be able to carry out photosynthesis effectively!
LEDs and Tomato Plants
In a lab setting, we tested the effectiveness of this new LED platform over tomato plants in a 4x4 growing area. Six LED lights (without other types of supplemental light) totaling around 200 W were hung over nine tomato plants. The lights were scheduled for an 18-hour on and 6-hour off cycle, and growth of the tomatoes was monitored for two months.
After a month the tomatoes began to flower under the LED lights. The light was able to penetrate down to the lowest levels of the plant, giving the amount of light needed for photosynthesis. In six weeks, the tomatoes began producing fruit even in the bottommost tiers of the plant. After the two months of testing, the tomato fruits closest to the roots were not only in abundance, they were healthy and large.
In a separate experiment, we doubled the intensity of the LED lights (about 400 W) over the tomatoes in their vegetative phase. As with the previous experiment, the testing was done in a controlled 4x4 growing area and closely monitored.
Although the experiment is still in progress, at the time of this publication, we noted the growth of the plant. Leaves grew wider with a darker green color, indicating high levels of chlorophyll, even in the lowest tier of the plants. With this added intensity, the tomato plants began to flower in just two weeks. The flowering stage for these tomatoes began early in comparison to the plants in the previous experiment, which began to flower after four weeks. It is clear that these tomato plants benefited from the extra boost of light.
The new dense matrix LED platform is coming to revolutionize the horticulture industry. Growers no longer have to depend on inefficient broadband sources for the depth penetration plants need. This advancement in LED grow lights will provide more intense light to produce tall and healthy plants. As a naturally cool light, growers can add even more LED lights to increase intensity to supply optimal light to plants. This platform is able to carry the plants from vegetation to flowering and fruiting, without having to use any additional supplement lighting. The light penetrating capabilities in combination with the spectral offerings of LEDs will give growers even more control over how their plants grow.
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.