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 and infrared (also known as IR or far red) light: Intensifying the total of IR in relation with 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.
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.
LED Grow Light Systems Pros and Contras
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.
