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LED Grow Lighting

Technologies used for plant lighting

There are several lighting technologies used for lighting in horticulture: HPS, CCFL, MH and LED.

HPS stands for High Pressure Sodium

HPS grow lights
HPS stands for High Pressure Sodium, it is currently the light technology most widely used in greenhouses. It has become widespread since 1990-s due to its high efficiency, longevity and reasonable price. Most widely used HPS lamps in greenhouses are 600 Watt lamps, however we can see move toward 1000 Watt lamps in recent times, as well as using 250W lamps for intercanopy lighting. HPS are considered most efficient grow lights on the market now.
Although having advantages, HPS technology has some disadvantages, too. As Mr. Sylvain Dube, a founder of a Swedish container farm company expressed it, “HPS spectrum is a disaster for plants”. Below is the attached spectrum of HPS lamps used in greenhouses.
HPS grow lights
As we can see, most of the light is emitted in green-yellow part of PAR spectrum, whereas plants better utilize blue (430-460nm) and far red (640-670nm) part of spectrum.
HPS lamp spectrum can not be adjusted, and dimming is a big issue, too. Apart from that, HPS lamps have very high power density and emit a lot of heat, so they can not be placed close to plant leaves, as they may burn them.

CCFL stands for cold cathode fluorescent lights

CCFL grow lights

This technology is mainly used now in lower power density applications like in indoor plant lighting systems, racks for tissue culture and cloning, aeroponic growing systems. Its advantage is quite high LPW efficiency, low heat generation, longevity. A decade ago, there were attempts to use CCFL lights as intercanopy lighting, however they proved this technology is not a good choice.

CCFL spectrum

As we can see, the CCFL grow light spectrum is quite poor and a lot of light also lies in green-yellow part, so it is not perfect for plants.

MH stands for Metal Halide.

MH grow lights
These lamps have a great part of light in blue spectrum and are mainly used for vegetative growth. A combination of HPS+MD lamps is considered a golden standard in marijuana growing. In other applications they are not so frequently used and their use for other plant growing applications can be neglected.
MH Spectrum

LED stands for Light Emitting Diode.

LED grow lights
LED for growing plants have been for a relatively short time by now. LED horticultural lighting is a new advanced plant growing technology that has taken off since around 2012, and has been slowly capturing the market. The latest LED grow light technology is a game changer in growing plants. In advanced LED grow lights the spectrum can be easily adjusted by choosing LEDs with the needed spectrum. Moreover, the intensity of each part of spectrum can be adjusted in the process of plant development, thus the grower can fine- tune it to the needed stage: vegetation, flowering, fruiting. LED grow lights emit less heat than HID and CCFL lights, this can be places closer to plants. Below you can see an example of a full spectrum LED grow light, where the whole PAR range with peaks in blue and red spectra is present.
The disadvantages of almost any emerging technology- high cost, lower efficiency. This can be said about LED lights for growing, but to some extent. Since 2012, the performance has greatly improved, and best LED plant grow lights can boast efficiency of up to 2,75umol/W compared to 1,9umol/W from best 1000 Watt HPS grow lights. In terms of cost, it has been improving now and we can expect it to be in line with HPS in 2-3 years.
Just as a simple example, LEDs now have taken a great part of general lighting replacing HPS in street lighting, CCFL and MH in indoor and billboard lighting.

What LEDs to choose for plant grow light

There is a great number of companies on the market offering LEDs for horticulture purposes. What we care about in grow light is spectrum, efficiency, longevity. Usually manufacturers use either discrete or COB (chip-on-board) LEDs for their lights for growing.
Discrete LEDs in grow lights- please pay attention to two things. First, the best way is to use brand LEDs like Nichia, Osram, Lumileds. These big guys have good R&D capability and can guarantee stable quality. Of course, these ones come with a price tag.
LEDs in grow lights
Second. If you want to save money, you may also go for “underbrand” LEDs made by Taiwanese or quality Chinese manufacturers. You may get half of the light from same power input compared to brand LEDs. But at least the quality can be trusted to, as they have some R&D capability and do tests before launching their components. Never use no-name LEDs, you are about 100% sure to get the product that will be of poor quality and have crazy degradation over 1000 hours.
LED grow light
Another thing- never consider wattage for LEDs. What you need to know is the current that goes through LED chip. For brand LEDs you may put up to 1A current, but for others you can be on the safe side with currents below 500mA. The more current you put, the more light you get, but it comes at the cost of efficiency. So it’s up to you to choose. We are on the brand LED side.
For COB LEDs- it seems a good solution for good color mixing and lower cost, but it comes at the price of efficiency and reliability. We prefer not to use them.
So, if you want efficiency, use brand LEDs with currents below 700mA. If you want lower cost and better color mixing, use COBs.

Cooling types in LED grow lights

LED grow lights can be either passively or actively cooled.
- Passive cooling is a type of cooling where heat is eliminated by natural convection. It is a cooling of choice for professional large scale growers, as it has no moving parts to break. The disadvantage is that heat sink of such lights for growing can be a bit heavy and bulky.
- Active cooling can be either forced air convection done by fan, or water cooled. Water cooled LED grow lights are relatively rare, as they are an advanced grow lighting system that needs plumbing. They are mainly used in cannabis growing industry, so quickly developing now in USA after being legalized in some states. The difficulty in using this kind of lights is that you need to make sure water temperature difference is not large on beginning and ending part of LED light system. You also need to store the hot water somewhere.
Fan cooled LED grow systems are very often used in LED horticultural lights that use COBs and in higher power LED grow lights above 100W. They are compact, relatively efficient and low cost. But they produce a lot of noise, do not have proper ingress protection from humidity and insects, usually associated with greenhouses. They are a solution of chose for growing plants indoors like at home and in smaller scale plant growing rooms.
To be continued...

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