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LED Grow Lights - Separating Fact From Fiction

As the cost of electrical energy costs continue to rise, growers are increasingly drawn to technologies that will allow them to operate at greater energy and life span efficiencies while maintaining or even improving upon crop qualities and times to harvest.  It is up to lighting manufacturers to be responsible and provide the end user with factual statements of values and not exaggerate or misstate their products capabilities.  To sum it up if the manufacturer is stating that they have the 'Greatest Indoor Grow Light' there is a pretty good chance that it is not any such thing.

 LED grow light manufacturers tend to advertise aggressively and make claims that their lights can deliver better crop results for far less energy than all other technologies, including induction lighting. When a manufacturer makes these types of revolutionary product claims it pays to be skeptical and to really research the data to see if the claims are even remotely believable. To that end you'll find an in-depth analysis at the bottom of this page where we examine the product information sheets of several leading LED grow light manufacturers to see how their claims measure up to the science.

LED's don't produce any heat. 

This is simply not true. Consider that only about 20% of an LED lamps energy is utilized for actual plant growth the rest is trapped as heat within the lamp housing.  That heat has to be removed from the housing or electronic components that drive the LED's will burn up.  Also the amount of heat generated by an LED is also directly proportional to the LED power levels. If you want to prove this to yourself try taking a Low Power 5mm LED array, wrap them in a towel and see how will quickly they’ll heat up since the heat would have nowhere to go. So while an LED won’t run as high a temperature as an HID lamp that creates both convection and radiant heat an LED does create convection heat and that heat still contributes to increased ambient room temperatures.

LED's don't waste energy because they only emit the spectrums your plants need.

Considering that sunlight is the broad spectrum light source and it has supported a variety of plant species for nearly 4 billion years, it would be reasonable to assume that the plant/sun relationship is both a dynamic and an intimate one.  As a result of LED's being narrow spectrum, LED lighting manufactures tend to reduce the importance of the natural symbiosis that occurs between broad spectrum lighting and plants by reducing the importance of certain spectrums or worse, eliminating them altogether.  

When comparing flowering results under narrow spectrum LED lights with broader spectrum HPS lights, studies such as the Emerson Effect, haveshown that the broader spectrum lamp source will benefit the plants natural photosynthetic processes.  When one widens the spectrum of the HPS lamp by including a Metal Halide lamp at flower many growers have seen crop quality increases as the plants are exposed to UV-B spectrums from the Metal Halide lamp that are missing in the HPS lamp.  This is precisely why we at Inda-Gro employ broad spectrum phosphors that allow our single induction lamp to be used from propagation through the flowering cycle.

LED manufacturers who rely solely on Chlorophyll Absorption Charts and don’t reference Net Photosynthetic Action Spectra data, or accept the Emerson Effect, do so because it’s not in their best commercial interest's to do so.  To illustrate this point you will see by the Emission and Sensitivity Curve chart on the right we show a plant sensitivity curve in black that shows the regions this plant would be absorbing energy in the wavelengths it requires for optimum growth. Next you can see by the regions the HPS lamp emits it covers a broader section under the sensitivity curve than the LED lamp shown in the red line. The LED by virtue of it's narrow bandwidth, would claim it is more energy efficient as they don't waste light unnecessarily in the least important 520-610 regions.  With that statement the manufacturer is being disingenuous since these are not regions that can be completely ignored in the interest of promoting energy efficiencies over plant response or competing technologies.   

The other problem that LED manufacturers face when relying solely on the chlorophyll absorption charts to promote their spectral values is that these ranges are set for isolated chlorophyll molecules suspended in a solvent and do not reflect total photosynthetic activity. Even within the Chlorophyll Absorption Charts, shown below, different solvents will give slightly different numbers.

LED's are better at directing their light to the canopy.

This is not necessarily a good thing.  That intensity can burn sensitive canopy leaves and create necrosis.  Also, as we have previously discussed,  the intensities reaching the canopy leaves are usually narrow spectrum.  When one takes into consideration the entire spectral width that a plant would be exposed to under sunlight we have to consider what an LED offers that would simulate the characteristics of the sun in an indoor gardening environment.  By their very nature LED's will emit a peak wavelength and will quickly fall off of that peak to a 1/2 peak of 10 nanometers on either side of that peak or 20 nanometers 1/2 peak bandwidth. 

Since plants absorb light within the 400-700 nm bandwidths for an LED to direct narrow spectrums of light instead of the broader spectrums like they would see in nature. The lack of spectrums may create stress conditions in the plants that inhibit normal photomorphogenisis that would not be seen under broad spectrum light source distribution. Narrow spectrum, highly directional LED's are inherently incapable of emitting the homogenous blend of spectrums as they would see in nature.

To illustrate our point about how much energy that LED will need to emit and then to direct that light to the canopy we can take a look at a project where leafy green crops are being grown under LED.  Ideally these plants would optimize crop production values with an accumulated amount of light at the canopy of 20 Moles/day.  This project was retrofitted to utilize LED bars that utilize 5 watt diode array's spaced at  approximately 4" on center.  The bars are placed at 24" on center which would cover a 2' x 4'grow area.  The manufacturer specifies that each F3 diode array emits a PPF of 7.5 uMole/s.  There are 12 ea.,  F3 arrays per 4 ft strip which provides a PPF of 90 uMole/sec over the entire length of the bar.  With what appears to be a 24" center to center spacing on the bars we can calculate that each 4 foot bar is emitting an average canopy PPFD @ only 121 uMol/M2-S.  

This is not alot of energy when you consider that leafy green plants optimize crop production values in the 20 Moles/Day regions of daily light absorbed or Daily Light Integral (DLI).  To meet a 20 Moles/Day DLI it would take a reading of 400 uMol/M2-S over a 14 hour photoperiod to achieve that value.  The 121 uMol/M2-S these LED strips emit, provide the plants with only 10 Moles/Day providing they are ran on a 24 hour lights on cycle.  What this amounts to is that the NeoSol DS would be meeting the very minimum accepted DLI/PPFD intensity levels for these crop types if they are ran continuously.

So how much energy does an LED need to meet optimum crop production values?

If you were take a 100 watt LED lamp putting out lighting levels of roughly 140 uMol/sec how far does that 140 uMol/sec of light take you? To put that energy into perspective, full sunlight is 2000 uMol/meter^2/sec.  As plants have evolved under these sunlight intensities the photo saturation point for many food crops is around 1000 uMol/meter^2/sec and most food crops thrive at 500 uMol/meter^2/sec especially in flowering. So for that 100 watt LED to reach an intensity of 500 umol/meter^2/sec would cover an area of three square feet (21" x 21"). So while the 100 watt LED lamp can definitely grow plants in a smaller area,  in a larger area, the rate of photosynthesis will proportionally go down.

LED's last longer than any other lamp technology.

Most LED grow light manufacturers will claim their lamps will last for a 50,000 hour lifespan. We’ve even seen others that have advertised 100,000 hour lifespans. To that I can only say that Chinese made LED lamps have had a very poor track record in meeting the advertised lifespans.  When they do fail early the warranty claims tend to be denied and blamed on a customer responsible heat management issue. Compounding these issues is that Chinese specifications or 'white sheets' are not always reliable.

For the grower to make an informed decision regarding the lifespans of that particular manufacturers LED lamp, they’ll want to identify two things from the white sheets and having been confirmed by independent testing labs;

  1. (L70) What is the Lumen Maintenance Level? This will be expressed as the L70 measurement and will be represented in hours and is the point where the LED lamps are giving off only 70% of their initial lumen output when new. Below this point they are considered ‘failed’ and should be replaced.
  2. (B50) What is the failure (mortality rate)? This is a statistical measurement of when 50% of the new LED lamps have fallen below the L70 lumen output threshold levels.

As a rule; the harder that you drive a LED the shorter its L70/B50 life will be as the higher temperatures lead to shorter lifespans. This is a hidden cost that one must consider when making a long term capital investment in an LED lighting system that costs anywhere from between $3-5 per watt.   When an LED does fail it affects your plants health with lighting downtime. To keep the downtime to a minimum and to get the LED grow lights back on the plants you have options; make the repairs yourself or return it to the manufacturer for the repair.  If you have a replacement LED lamp and are able and willing to replace the failed lamp, which has been soldered onto the fixtures circuit board. Assuming you can get the proper replacement part you’ll have some down time while you install the replacement LED lamp.  Otherwise you’ll be sending the entire fixture back to the manufacturer and if it’s still within the warranty period, would hopefully make the timely repair or replacement without having to ‘regretfully inform you that the fixture is no longer within warranty period’ or determine ‘customer responsible failure not covered under warranty’.

Of note: on March 18, 2010 the US AIR FORCE issued a memorandum in which they removed LED lamps as an option for energy retrofit area lighting projects as a result of many of the LED installations having proven themselves to not have delivered sufficient lumen levels and not having met the published L70 and B50 standards within previous installations.

Conclusions:

We’ve found that LED's work very well in triggering certain narrow spectrum photochemical responses and in areas where the lamp to canopy spacing is close due to shelve spacing.  But LED diodes by design will emit in narrow spectrums so they will be, when compared to a broad spectrum phosphor lamp such as ours, at a competitive disadvantage in emitting broad spectrums with enough intensity to optimize plant response over a large area.  We are of the opinion that hybridizing LED and Induction phosphors can broaden the spectrums with intensities that improve crop quality and yields while reducing energy consumption is the ultimate best use of these technologies.    

We could spend an eternity exposing all of the claims we see made by various manufacturers regarding what they claim their LED grow lights are capable of.  In the interest of addressing some of what is out there we decided to pick three of the leading US manufacturers of horticultural LED grow lighting products and take the reader through a technical analysis of their statements from information which can be found on their websites.  The focus of this analysis is help the reader determine the accuracy and consistency of claims, background data supporting claims, and general reasonability of the claims these manufacturers are making.

Click the manufacturers logo to read the analysis

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