Hey guys, I was doing some research the other day and came across this article and then today I saw this thread so I figured I'd share it with you guys..
In a previous article, I concluded that LEDs were a viable technology for providing artificial light energy to fuel the photosynthetic response (plant growth). However, there were some limitations. The dual band spectrum provided only red and blue light wavelengths. While these bands are where most of the photosynthetic response occurs, making LEDs very efficient, there is some other activity that occurs in other spectrums of the visible light bandwidth.
Imagine this: blue and red wavelengths of light are like the macronutrients, in terms of fertilizers, while other bandwidths are more like micronutrients. Micronutrients are just as important as macronutrients; the big difference is that they are used in much smaller quantities than macronutrients. So, its about supplying the correct and exact ratios of each. HPS and MH lighting produce huge quantities of their output in spectra that the plant uses very little of, making them much less efficient although effective because they are full spectrum.
Furthermore, the exact spectral output of the diodes, measured in nanometers (nm), has been fine tuned in next generation LED lighting so that the output occurs where the most light energy intensive reactions occur. In order to provide a complete, although not very intense, full spectrum light source with first generation LED grow lighting, the LEDs were supplemented with full spectrum CFL or T5 fluorescent lighting to meet the needs of the photosynthetic response on all the necessary wavelengths.
Quad Band LED Spectral Output (327 Watts)
When compared against the known photosynthetic response curve, quad band LEDs maximize the areas of highest photosynthetic activity in their output.
The result using the first generation LED lighting was a source of light for plant growth that used a minimal amount of electricity and delivered the required wavelengths of light to sustain healthy plant growth. It was also noted that different types of plants seemed to require different wavelengths of light at different times. The earlier LEDs were capable of producing healthy growth for rooting cuttings, young plants, seedlings and vegetative growth. The growth was exceptionally healthy and hard and supported relatively rapid development.
The first generation LED units provided an exceptionally cool running growing environment, which allowed for the use of supplemental CO2 enrichment to be applied very easily and cost effectively; further accelerating growth rates, plant health and yield potential. In our early test model, we were able to maintain CO2 levels of between 1200-2800 ppm in the growing environment by the use of fermentation in a sealed hydrohut (grow tent). Noticeably faster growth rates occurred, and the by-product of the fermentation, beer, was an added bonus. Not only was this set-up low in energy requirements, it was very economical and very quiet, an important consideration for those urban growers who live within close proximity to their gardens.
The earlier LED set-ups delivered good results relative to the amount of electricity they consumed, although HPS and MH High Intensity Discharge lamps seemed to win in terms of yield in the bloom phase. They also produced a lot more noise, heat and at least triple the electrical consumption when factoring all of the peripheral equipment required to manage the heat levels the HID lamps produced. To be fair though, if the earlier dual band lower wattage systems went watt to watt with the HIDS, they were capable of surpassing yields and crop quality in many types of plants. One drawback was that certain types of plants that had a definite finish in their life cycle sometimes took prolonged periods of time to ripen; this was attributed to limitations created by the dual band spectrum, although supplemental full spectrum fluorescent light alongside of the LED panels helped to improve upon this issue.
Due to their relatively lower intensity, and therefore limited ability to deliver high levels of light energy over distance travelled from the source of the light (diodes), it was recommended that those interested in gardening with such LEDs select auto-flowering plant varieties that mature under longer photoperiods and finish relatively shorter in stature, for example, less than 18 inches tall. This way, the plants were able to receive significant light levels from top to bottom, providing more consistent quality in all fruits and flowers harvested from the crop.
It appears that LEDs are ready to give your crop everything it needs for high yields and vigorous production in bloom.
So, here we are today, with the next generation of LED units for plant growth in hand. It truly is amazing to see how much the technology has improved and evolved in such a short time span. I was amazed at how bright the first generation units were relative to the amount of power they consumed. I was nearly blinded by the intensity that the next generation LED panels produced; and this is coming from someone who has spent far too much time around bright HID lighting!
1A-HPS VS Quad Band for Photosynthesis
Looking at this chart, we can see that quad band LEDs appear to be better tailored to the known photosynthetic response curve VS HPS lighting.
In fact, the model tested for this article draws approximately 586 watts of power, yet produces 30 per cent more initial light intensity than the sun, and has double the output of a 1000 watt HPS lamp at equal distances from the light source. These intensities have been carefully measured in the 610-680 nm range using a highly specialized light meter; this is where most of the photosynthetic response for reproductive (bloom phase) in a variety of crops occurs. Consult Chart 1-A in this article to compare the relative spectral output of this new quad-band LED growth technology to a horticultural HPS lamp, while also comparing to the known photosynthetic response curve.
Not only is this lighting technology incredibly bright, it has been engineered as a quad-band spectral output to ensure that all of the necessary wavelengths for all types of plants are being delivered, allowing plants to complete their natural life cycle similar to HPS and MH illuminated gardens. This is an especially important consideration for the ripening phase for crops in the bloom cycle. The unit featured here produces light in the following ranges: 455-475 nm (blue), 620-630 nm (red), 660 nm (far red) and bright white (full spectrum, 2700K).
There was never any question as to whether LEDs were effective for vegetative growth. It now appears that LEDs are ready to give the crop everything it needs for high yields and vigorous production in bloom: intense light levels in balanced spectral ratios while eliminating what the crop does not need - excessive heat. All of this with about half the power consumption in lighting alone, and significantly reduced costs in cooling equipment required and the relatively high level of electricity required operating energy intensive appliances such as ACs, chillers and industrial fans.
Not only are there more diodes in this unit versus the first generation of LEDs discussed, they are of higher wattages. The diodes themselves are approximately two watts each, although the power they are driven to is dependent on the individual spectral outputs engineered into each of the different LED chips on the lighting board.
These cutting edge LED chips are driven at much higher frequencies than previously with earlier diode technologies used for plant growth. The difference is significant. Now the chips can be driven at hundreds of milliamps instead of tens of milliamps; this fuels the process at which electrical current is passed through the chip and energy, called electro luminescence, is released. In laymens terms: bigger LED chip + more milliamps = very bright light versus first generation LED crop lighting. While more milliamps are being passed through the individual LED chips, the overall amount of power consumed is still relatively very low to the intensity of the light produced, making the next generation of LED crop lighting technologies very efficient.
HPS Lamp Spectral Output (1000 watts)
HPS lamps produce a lot of yellow and orange in their spectrum, falling short in the red and far red wavelengths relative to the overall output.
Now with all of this output, surely there must be a lot more heat? The answer is no, not really. Even at more than 10X the light energy output versus the earlier 45 watt dual band, smaller wattage diode panels, these higher wattage LED systems run incredibly cool relative to their light output, retaining all of the benefits from the first generation of LEDs while delivering a broader and more intense source of light for bigger yields and faster finishes.
As with the smaller wattage first generation LED units, the very small amount of heat that is produced by LED lighting originates mostly from the electronic driver that regulates the amperage (milliamps) being directed to the individual diodes in the arrangement on the light board. One difference, however, is that the high output second generation light system is heavier. The internal circuitry is cooled with several small computer-type fans. They run so quiet that they are barely audible, making second generation LED lighting systems much quieter than conventional core and coil ballasted HID lighting systems, as well as quieter than some models of electronically ballasted HID lighting systems. High power LED systems run cool for the amount of light they produce, so it is possible to construct a garden in a wider range of locations, because noisy fans and extensive duct work for cooling purposes are minimized or eliminated.
The space for growing crops does not require as much vertical clearance, or conversely, taller plants can be grown in rooms with height limitations. The high powered LED fixtures can be placed very close to the ceiling and the LEDs run cool enough that, if necessary, plants can grow very close the LED light source. Conventional HID lamps require significant clearances from the top of the plants to prevent overheating, and require significant clearance distances from ceilings for safety reasons. The additional clearance requirements for HID lamps can limit the vertical space for crop growth in tighter spaces as a result.
It would seem things are looking very promising for this latest generation of high-powered, quad-band LED crop lighting systems. In the next couple of installments, we will put the technology through its paces, and take some comparative measurements versus traditional indoor crop lighting systems such as HPS, MH and high output fluorescent lighting.
LED lighting for crop growth may very well revolutionize the way we grow plants indoors, and allow for just about anybody, in any type of space to be able to set-up a highly efficient and productive indoor garden so that anybody with an affinity for all things leafy and green may enjoy fresh healthy harvests of their favorite plants any time of year. Stay tuned for part two in the series to learn more about this rapidly evolving technology.
