Growing Plants with LED’s
All these resources are an abundant presence on Earth, but nothing can last forever. Polluted water is not usable, air is itself contaminated on many parts of the Globe, mineral resources are non-renewable and lightâÂ?¦ natural light has its benefits but also it can constitute a danger for the species if we consider the UV emissions reaching Earth’s atmosphere.
Light influences all life on Earth directly or indirectly. Plants need light for photosynthesis, therefore for growing and in exchange they forward their energy to the animals that consume them. At the same time animals need light for a harmonious evolution and even nocturnal ones require some low level illumination. Lack of natural light causes various disorders by people and the same happens by plants and animals.
UV light can harm living organisms in several ways. For example plants overexposed to UV light reduce size and are more susceptible to specific diseases. The light coming direct from the sun sends to earth three types of ultraviolet: UV-A (380-315 nm), UV-B (315-280 nm) and UV-C (280-10 nm). Due to the absorption in the atmosphere’s ozone layer, 99% of the ultraviolet light that reaches the Earth’s surface is UV-A.
While UV-A causes plants only a little harm, UV-B, which is a shorter wavelength, can damage plant tissue and in humans it can cause skin cancer. UV-C is the part from the UV spectrum with the shortest wavelength and all bacteria and virus get deadly sunburn in an artificial UV-C filter system. Certainly UV light has its paradoxes: even if it is harmful in one way, it is useful in another. Medicine is using this artificial UV light to cure difficult skin conditions such as psoriasis eczema, lymphoma, acne, a-topic dermatitis, and so on.
Fact is that plants don’t need too much UV light, on the contrary. This is why crop production with artificial light means that will eliminate the dangerous UV emissions seems to be the next logical step.
Growing Plants Technology – Crop Production Systems
The target of crop production systems is to develop innovative technologies that lower the costs of harvest and ensure ecologically aware crop farming.
The crop production systems do not disregard important factors that influence plant development: temperature, humidity, light, carbon dioxide, water and nutrients. All these blend to create the ideal environment for a plant to grow and reproduce as well as they influence size, seeds, plant health and so on. Each plant will progress in its own manner, depending on the environment. Since a long time already biologists are studying the factors that influence vegetation’s evolution. Light is a very important factor and researchers were able to determine exactly which wavelengths are the ones plants need for their growth. Some colours in light rays are essential for good plant evolution. Vegetation mirror and receive a small amount of energy from yellow and green emissions of the visible spectrum. However the red and blue fractions of the light continuum are the most valuable energy resources for plant life, and plants necessitate more red (625 to 675 nm) than blue (400 to 470nm). Yellow (525 nm) triggers photosynthesis too, while IR influences seed spurring and UV colour and scent.
How Light Colour Influences Plant Growth
Blue light: plants react to the intensity of blue light. Lessening the blue light will cause poor growth – the strength of the radiation in any other part of the spectrum is not as important as the intensity of the blue, which shapes height and quality.
Red (660 nm) and infrared (730 nm) (also known as IR or far red) light: Intensifying the total of IR in relation with 660 nm red makes plants grow tall and thin. On the other hand if red is increased while IR diminished, plants will be short but thick. Plant reactions are not linear with the red/far red ratio and they can also vary in their response to red and far red light.
Ultraviolet light (UV): While overexposure is dangerous, small amounts of UV light can be beneficial for the flora. In many cases UV light is a very important cause for colours, taste and aroma. But UV-C and UV-B are believed to stop plant spread and this is why they have to be removed from the light under which plants are developed in green houses by UV stabilisers or glass. Removal of the UV up to 400nm is might be effective also in case of virus carrier insects (as insects see partly in UV).
Direct light from the Sun distributes the useful wavelengths only on special times of the day and in small quantum enough for a harmonious growth in some parts of the Earth, yet not enough on others.
Crop production systems are dealing with such problems and find ways to replace natural light with artificial light. The idea of growing plants under artificial illuminators is not new at all. Long time ago NASA started to grow plants in space, and the results were astonishing. Nowadays we know that by using the correct wavelength plants develop harmonious and healthy, sure if they have all the other conditions ensured. Yet getting light of the correct wavelength is not an easy task, especially if one takes into account the costs and efficiency of such light sources.
LED Lighting Technologies to Substitute Natural Light
To substitute natural light is quite difficult also if you consider how hard it is to obtain light near the visible part of the spectrum with traditional luminaries. Light emitting diodes are here to change that difficulty.
SSL (solid state lighting) is the youngest lighting technology and by now is believed to be more efficient than incandescence and fluorescence due to the fact that SSLs produce light at or near the visible part of the spectrum and as a result the emitted light can be used straight or with minor conversion. One of the most important advantages is that SSL technology has eliminated damaging components from the light sources (remember: light emitting diodes contain no ultraviolet unless they are produced as UV LEDs).
NASA is already using SSL in its space farming systems. The reasons are quite simple: incandescent or fluorescent lamps are not efficient enough for such purposes, because they consume a lot of electrical power, generate heat and contain electrodes that burn out (maintenance costs are high). This is why NASA’s plant physiologists started to work with light emitting diodes (blue and red) to grow salad plants such as lettuce and radishes. The researchers found our that blue and red light is essential for plant growth and, in general, a percentage of 8% blue LEDs and 92% red LEDs, both with the same frequency and relative intensity per LED, are enough for a harmonious evolution. Blue has a smaller influence than red; however a percentage between 1% and 20% of blue light can be selected, depending on the plants and their growth requirements. The NASA scientists have tried to create the most cost and energy efficient light sources possible, and this is why they have eliminated from the fixtures other colours normally found in white light. “What we’ve found basically is that we are able to limit the amount of colour we give to the plants and still have them grow as well as with white light.” said the research scientist Greg Goins of Dynamac Corp. LEDs are not the only ones efficient for growing plants: sulphur microwave lamps are the most efficient light sources known to man, that can generate as much light as the noonday sun, perfect for illuminating large-scale systems such as greenhouses. For smaller applications, such as indoor gardens, LEDs seem to be the right choice.
Pros and Contras LED Grow Light Systems
There are some pro and contras when it comes to LED grow light systems. When planning such farming alternatives, one has to carefully consider that plants do use light at all wavelengths from UV to IR, as explained above, needed to convert water and carbon dioxide into sugars. Some plants use more red and blue, less green and yellow, while others use green as much as they use red and blue, as well as the light in between. If LEDs are chosen for brightness, there is one aspect to be underlined: they just look bright because their light is unidirectional and their size is small. To get enough light there are many LEDs needed, that’s why the cost of LED arrays or LED modules is so high. LEDs can be calibrated to emit only the light most efficient for the plants, but not all the light plants need. This is why such light sources are recommended only in places where direct light from the sun is not enough or inexistent – space farming for example. Also in places where light from the sun is too strong and can harm the plants with the high emission of UV, LEDs are a good choice, because UV filters are stopping some of the useful wavelengths too. In wintertime the weather conditions restrain crop production; this is why greenhouses need a substitute for the natural light. It makes sense to deliver plants the minimum lighting conditions for a corresponding evolution.
There are some significant factors to take into account when choosing light sources for such applications and these are low costs, energy efficiency, long life, and ability to withstand voltage fluctuations, modularity in order to grant users the possibility to assemble arrays that gives as much light as needed, where needed. LEDs are pretty efficient in the conversion of electric power to light, in any case more than traditional fluorescent and incandescent lamps. Due to the fact that light emitting diodes can be manufactured to emit a specific wavelength and are expected to have a long life span (from 50000 hours up), many plant physiologists are considering using them in large applications. Compared to LEDs most of the other traditional lamps have to be replaced every two-three years. Other features such as choice of viewing angles, control options, instant turn on times, cold start and much more, recommend the semiconductor devices. At present this is still an expensive technology, but in time LEDs efficiency will be maximized while prices reduced and these details are a good base for future planning.
It is so far clear that in order to produce efficient LED grow light systems a lot of investigation is necessary. It is not enough to mount some blue and red LEDs on a PCB and say: “that’s it; we’ve got the plant growing LED system”. NASA created only a mechanism that delivers the minimum amount of light needed for some plants. For greenhouses on Earth other questions need to be answered: how much blue, how much red? What about the other colours, what about UV and IR? Should the light pulse? Should it be dimmed in the morning and evening to imitate natural conditions (sunrise and sunset?). Do plants need light at night? And the list remains opened.
