Three and a half years ago, I wrote a series of articles on light emitting diodes (LED) grow lighting for Maximum Yield magazine. Since then, I'm guessing many of you have read quite a few subsequent articles in relation to LEDs; however, you may appreciate this one because I'm writing from the standpoint of an end user, and I have had the same fixture(s) I wrote about previously in operation on and off, at various locations, growing a variety of crops, since I had the pleasure of initially discussing this subject with Maximum Yield readers.

So, in short, this jury has reached a verdict. Now, since so much time has passed, it is important to distinguish the fixtures being described as what I would call the second or third round of commercially available LED grow lighting to become available to hydroponic enthusiasts, from the first generation.

First generation LEDS used very low wattages, and while they could sustain plants, there wasn't the intensity in growth that high intensity discharge (HID) gardeners are accustomed to seeing. The units I am referring to in particular here are the “SG” series. These are quad band, high output LED grow lights that I have tested as 602 and 1202 models. Both veg and bloom (or “all around”) spectrum variations have been in use since those early “Quad Band LED” articles first appeared.

Initially, and perhaps still today, there were strong opinions formed about how effective LED lighting could be for highly productive indoor gardens, where it was applied as the sole source of light for growing and blooming crops. Interestingly, some of the opinions were rather strong, considering it was such a new technology available to growers as well as the fact that there were so many different models and variations; it was like no two fixtures were near the same.

There is still much confusion when it comes to LEDs and growing. Largely, this is attributed to the fact that there is no standardization amongst producers of LED lamps for growing. HID technology is highly standardized in comparison, which can be expected since it has been available since the earlier parts of the 1940s. Another part of the confusion arises from how the lighting is actually being applied to the crop.

LED light appears to behave differently in growing applications versus HID or T5 Florescent lighting. So, if a grower, with no reason to believe they should be doing otherwise, applies the lighting as they may have with other methods, there is a possibility they will not see the benefits as readily as others who have thorough experience, who have “dialled it in” and are loving the results.

OK, so now let's move forward after that quick shoulder-check looking back. Here we are today in the midst of 2013, and the SG-Series fixtures have been rocking out crops for over three years now.

Here's the consensus:

The Quad-Band High Output SG-Series fixtures, watt for watt, have outperformed conventional HID lighting in limited trials. Where some adjustments to previous thinking has occurred is in the area of electrical efficiency versus HID lighting. My trials have shown it takes a few more watts of LED lighting per square foot of growing area than previously considered.

However, the informal test results demonstrated that these gardens still needed fewer watts of LED lighting from these fixtures to achieve the same yield or better versus the same wattage of HID grow lighting. In addition I have found further savings in electricity when I weigh-in that less cooling power is required, because watt for watt, LED growing lighting operates considerably cooler.

Your LED grow light can do things for your plants your HID probably never will be able to. Straight-up. The difference in harvest quality can be astounding. That's not to say you can't produce good quality harvests with HID lighting, because we all know that you can. However, the difference has been very significant. In a couple of informal tests, people always picked the LED-grown produce when offered the same variety from the same room, with the only difference being the source of light.

Why, you may ask? LED diodes can be configured to provide wavelengths of light that HIDs cannot. View your light wavelengths like you might your hydroponic fertilizer. Some are more complete than others and the differences can become evident very quickly. Simply put, HID lighting is slightly deficient in spectra versus natural sunlight.

LEDs can not only deliver these needed wavelengths, but can deliver proportions of specific ones that the sun can't, making it possible to tailor a crops “light diet” to perfection. There is a misconception that LEDs can't produce firm fruits and flowers, but I have found this not to be true. In these tests the LED-grown was always firmer in the same environment.

Are they cost effective? This is a big factor to consider, and it's probably one of the more weighty factors in why you may not be growing under LEDs right now. A quality LED grow light isn't cheap to produce compared to other light sources.

This makes LEDs about four or five times more expensive versus HID lighting when setting up a grow room. However, that's only the sticker price, which is something that can be hard to see beyond when you haven't seen the differences first hand.

When you see that you don't have to buy and power additional equipment, the price difference starts to narrow in some cases. Eventually, LED could be a more affordable option when you consider the power savings (about 30% less wattage required) and the fact that you don't have to replace the diodes like you do with HID lighting.

To date, there has been no loss of measured light intensity being emitted from the diodes after over three years of regular use in a variety of situations, where power quality coming in may vary.

Reliability has been excellent. The units have survived electrical traumas that digital HID ballasts did not. To date, about 5% of the drivers (each fixture uses several drivers, so if one goes out, it's just a few of the diodes that stop lighting up) have quit.

That's over three years, and some of them arrived not working, likely related to rough handling by commercial carriers with heavy, bulky-but-fragile packages. But not once did any of my gardens have to stay in the dark due to equipment failure relating to LED lighting.

What about yields? Yield per watt with the SG-Series fixtures has been higher than HID grown harvests, on a variety of plant types and in a variety of growing situations where the LED light fixture was being applied correctly (which was correct in almost all of the instances).

To date, the average amongst different growers trialling these particular LED grow lights with different strains has been that for about 600 watts of power, you can yield just under what a 1000W HID lamps is capable of with a big difference in quality, in favor of the LED grown harvest.

So from these trials, a fair estimation might be to say that a 600 W power draw from an SG-Series gave the same weight as the power draw from about 800 watts worth of HID lighting, but with a lot more advantages than just the power savings on lighting only, as highlighted above.

It has been noted here that LED light seems to behave differently in the garden versus HID light, and that it was important to apply the LED light correctly to maximize the benefits that make LED lighting payback respectable for growers who make the investment.

Next, we talk a look at some specifics learned during three years of hardcore trials in a variety of real world gardens.

Grow a variety with a more “open” plant structure. A common misconception is that you want to keep the growth as tight as possible under LEDS. This is not so. This isn't to say you aren't going to produce solid and firm flowers, fruits and buds.

It's because plants absorb the “cleaner” wavelengths of LED light more readily. HID light seems to have a ricochet effect as it bounces through the plant canopy, off the wall as reflection (likely due to the fact that the radiation needs to be converted into other wavelengths by bouncing around before it may be absorbed).

LED light just seems to get absorbed more directly, hence the advantage of an open plant structure so that individual flowers, fruits and buds get even lighting.

Work your plants. When grown under HID lighting, plants transpire a lot of moisture due to the cooling required, which tends to dry the air and keep the air moving at a steady pace of the leaves, where plants release moisture into the air as they draw it up from the roots to replace what has been removed.

This is part of what makes HIDs work for growers. With LEDs you will need to push your plant a little harder, because they run at cooler temperatures, lessening the demand of water on the plant (which can be handy where water is scarce).

Keep a steady flow of air from an oscillating fan trained on the plants, and add another DE-humidifier or two to your grow to dry the air a little more than you might try to with HID lighting.

Maintain an even plant canopy. Because LED light for growing tends to originate from a flat and linear source, so should the profile of your garden in order to receive as much of the light at an even intensity as possible.

Reduced air exchanges: Adding the CO2 advantage. If air exchanges are minimized or eliminated by installing cooler running LED grow lighting, you can take advantage of the fact that air exchanges are lessened and supplement the air in the growing environment with carbon dioxide. Supplemental CO2 levels will speed up growth and increase your yields. As much as an additional 30% can be realized when adding CO2, provided it is managed correctly.

Prune to maximize light penetration. Just like any garden you grow using an artificial light source, it's a good idea to trim off lower plant parts that aren't receiving strong light as plants get taller. Typically, after plants reach a height of over a couple of feet, experienced growers know it's time to start removing the lower, spindly material, which is typically the lower third of the plant that has been stripped before maturity.

As a final note, there are plenty of great grow lighting systems out there. The one discussed here is just one of them. Keep in mind there can be some big differences from manufacturer to manufacturer and even from generation to generation within a particular model.

It is the intention of this article not to call attention to any single design or product, rather, share the results after over three years of intensive testing on a technology I was pleased to bring to you years ago.

Hopefully this review of LED lighting inspires others to grow forward and experience new growing methods and technologies, both of which can lead to highly rewarding experiences.