7 Key features you should know about LED grow lights: Choose right

 

7 Key features you should know about LED grow lightsCompare LED grow lights and choose the right one

Like many new technologies, the range in prices and quality of LED grow lights is wide, and that can make choosing your best option challenging.

How can you choose among all the LED grow lights and get the right one for you and your plants?

Here are some of the most important things I’ve learned from working with LED grow lights, written in language that's meant for plant-people. If you’re new to LEDs, I hope this can speed your learning curve. And if you’re an expert, please share comments that can also help people who are just entering this remarkable new grow light era.

Why choose LED Grow Lights?

Before going further, there is one obvious question: Why should anyone switch to LEDs for grow lights? After all, they are typically more expensive.

Answer: Choose to grow with a high-quality LED grow light because your plants will thrive, your electricity bill will not climb, and LEDs are better for our environment than other types of grow lights. From the Illuminating Engineering Society’s online introduction to lighting basics (which has no marketing agenda) we can learn several key reasons why LEDs are quickly transforming the grow light world:

“LED lighting is fundamentally different from conventional light sources such as incandescent, fluorescent, and gas-discharge lamps. An LED uses no mercury, no lead, no gas or filament, it has no fragile glass bulb, and it has no failure-prone moving parts. LED sources are super green! They do not contain mercury (as do CFLs) or lead (as do incandescent lamps). LED lighting is more efficient, durable, versatile and longer lasting than incandescent lighting. … In a well-designed product; LEDs are basically cool to the touch [and emit visible light as specific colors].” Source: http://www.ies.org/lighting/sources/led.cfm

Robert Morrow, of Orbital Technologies Corporation, wrote in an article for the journal HortScience, “… the use of light-emitting diodes (LEDs) is potentially one of the biggest advancements in horticultural lighting in decades.”

A bit of context

How did LED Habitats LLC arrive in the world of LED lighting? Choosing and designing the right lighting for plant growth and flowering has been part of my husband’s job since the ‘90s, when he began working at the University of Wisconsin-Madison with a Brassica research plant called Wisconsin Fast Plants. These fast-growing plants are grown indoors, under 24-hour electric light, and the quality of the light has a huge impact on their growth and health. Through this work, Dan (also co-founder of LED Habitats LLC) was involved in a NASA project that included sending Fast Plants into space for experimentation. That project introduced Dan to the world of high-tech lighting solutions, as an innovative partner—WCSAR—designed the growth chambers for use on the Shuttle. Since then, Dan has designed and tested a wide range of lighting systems, leading up to work with LED lighting that became possible when blue LED lights were invented.

During the past several years, Klaus—also co-founder of LED Habitats LLC--and I stepped into Dan’s search for high-performance LED lights. Each of us brings a different type of expertise, and all together—along with professional LED lighting engineers with whom we work—we are thoroughly immersed in the world of horticultural LED lighting.

Wavelengths emitted matter for LED grow lightsWavelength output

I’ve read a lot on the web that claims plants cannot grow in LED lighting. At one time, such claims were correct, but that changed with the breakthrough discovery of blue LEDs. To appreciate the importance of blue light for horticultural lighting, let’s review some of the physics of light.

Usually, when we talk about “light” we mean the part of the Electromagnetic radiation spectrum that is visible to the human eye. For plants, there are certain wavelengths that we’ve learned through experimentation are particularly important for photosynthesis, growth, and development. The term PAR or photosynthetically active radiation is defined by the range of wavelengths that scientists have determined are important for plants, and iElectromagnetic spectrumt corresponds with the visible spectrum (the light wavelengths the human eye can see).

Within the PAR range, experiments have shown that certain wavelengths promote plants to grow vegetation and/or flower, and some wavelengths may also hinder growth in some species of plants. Scientific experiments demonstrated that red and blue light wavelengths are especially important. So, until Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura invented the blue Light Emitting Diode (LED)—for which they were awarded the 2014 Nobel Prize for Physics—we simply could not make horticultural lighting with LEDs alone. And, we continue to learn: for example, we now have research showing the physiological importance of light throughout the spectrum (including some wavelengths outside of the PAR region).

When shopping for LED grow lights, the wavelengths emitted are critical. An LED light sold for a shop light or lamp (for human lighting) was designed to work well for human vision, not to emphasize the blues and reds that we know plants need or necessarily include the whole PAR spectrum.

Habitat engine LED Spectrograph-PAR LED Habitat's LED engine output readings taken with an Ocean Optics USB2000+

If an LED grow light manufacturer claims their light provides the perfect spectrum for your plants, well that's pretty arrogant. Such claims are called out by highly-respected researchers, Snowden, Cope and Bugbee in the first sentence of their 2016 research paper: “Despite decades of research, the effects of spectral quality on plant growth, and development are not well understood.” And so, for our LED Habitat grow lights we chose to include:

  • the full PAR spectrum with emphases in blue and red wavelengths,
  • those wavelengths that testers preferred to see (their plants looked beautiful!) and
  • wavelengths that we tested, and our plants thrived--both when growing and flowering.

There’s more to come about this below.

Watts are less significant for LED grow lightsUnderstanding Watts

Watts tell us how much energy input a light requires. When most all lighting was incandescent bulbs, then Watts were a useful measure because the electricity input was directly related to the total light intensity output, which is measured in lumens.

watt-meter-LED_Habitats 24.8 Watt input for an LED Habitat

Here is a useful definition of Watt from the Illuminating Engineering Society (IES): WATT: A watt is a unit of power denoting the rate at which electricity is used.

However, the light output of an LED light is not simply a function of Watt input. Instead, it is determined by the quality of its components and overall design, including the particular LED chip used, chip density, optics used, heat sink, and the driver. In fact, LEDs become less efficient as wattage increases because increased temperatures in the electronic circuit board containing the LEDs (the backplane) cause significant decrease in LED efficiency. In other words, an LED driven at 3 Watts emits about three times less light than the same LED driven at 1 Watt!

PAR_meter_reading LED Habitat PAR output measured with an Apogee Quantum sensor at typical distance to plant tops is consistently >420 µmol m-2s-1.

In summary, if an LED grow light manufacturer is boasting about Watts as a measure of their amazing ability to grow terrific plants (and not as a remarkably low input), be suspicious. An upcoming article: Proposed Product Label for Electric Lamps Used in Horticulture and Plant Biology that is due out later in 2017, in the HortTechnology Journal, may help “illuminate” better standards for describing and comparing LEDs. However, until standards are adopted, we must depend on manufacturers to provide as much information as possible, including Watt input and PAR output.

Our LED engine (one engine/LED Habitat, three/Habitat Pro, and four/Habitat 420) draws fewer Watts than a 30W light bulb, yet it is far brighter (higher lumens) and has a consistent PAR output of >420 µmol m-2s-1.

Read on for better ways of comparing LED grow light outputs.

Lumens, PAR, and lux: not all relevant for LED grow lightsLumens, PAR, and Lux

As mentioned in the previous section, light manufacturers, hobby growers, and professionals in horticulture use different terms to describe grow lights, and that makes it challenging to compare different light systems. What follows is a straightforward discussion about the types of measurements that are commonly used in electrical lighting and their significance for your plants.

Lumens are a unit of measure describing the total quantity of light from the visible spectrum that is emitted from a source of light (in all directions). But what matters most isn’t how much light a grow light can emit—it’s important to know how much light will actually reach your plants. Illuminance is the measure of the quantity of light that reaches a surface and is defined as lumens per meter squared or lux. However, lux is a human eye measurement and not recommended for plant applications--though there are conversion factors that can be used to convert it to micromoles (and other light units).

Key is the difference between how humans sense light intensity (measured in lumens) and the way plants absorb and use light. This difference is why we really have to measure the light output from grow lights with different types of meters than those used to measure the light output from lights intended for humans. PAR photon irradiance (often abbreviated as just PAR) is the measurement that gives us the most useful information for comparing grow lights. The recommended units of measurement for PAR, µmol m-2s-1.

So, if an LED grow light describes output only in terms of lumens, know that you’re only getting some of the information that is useful for choosing a grow light.

LED-Habitat-engines-paintdaubs

High quality LED grow lights will provide you with information about the distribution of the light wavelengths that are emitted by the light, the size of area intended to be illuminated, and a measure of energy available for photosynthesis (PAR photon irradiance) at plant level. The most accurate instrument for measuring a light’s output is a spectroradiometer, and some grow lights include in their specifications a graph of the wavelengths emitted as measured by a spectroradiometer. However, spectroradiometers are very expensive instruments that are seldom used by light manufacturers who lack plant biologists who understand their value.

While designing our LED array, we were fortunate to have access to a spectroradiometer for testing prototypes because we were also using our LEDs in our university plant research. Pictured are the results, showing the full spectrum output.

If you’d like more detailed info about PAR, lumens, lux, measuring/reporting environmental parameters for plants, and more, you’ll find a list of resources from reputable sources that are available online at the end of this article.

Distance from light source effects LED grow lightsLight intensity

If you have access to a light meter that measures lumens, lux, or PAR, try taking measurements at different distances from any type of light source. You’ll soon find that as you move your meter farther from the light source, the light intensity quickly drops.

light output spreads and declines in intensity with distanceThis relationship between light intensity (output) and the distance from a light source is well understood as a physical law, (called an inverse square law) and the light intensity for every grow light behaves the same.

It’s important to know this when comparing different grow lights. If a manufacturer boasts about lighting a large footprint, and the LEDs must be positioned high above the plants to spread light throughout that footprint, then the light’s output must be far greater than if the lights are designed to be kept close to the plants, and you can expect that light intensity is likely lower at the edges of the footprint.

What you can easily look for when comparing lights is that high-quality LED grow lights typically boast about how close plants can be grown to their light source. That’s one of the reasons why LEDs are transforming horticulture—because well designed LED grow lights run cool enough that leaf tissue can practically touch the LEDs without harm, so the lights can be kept extremely close to plants where light output is highest (with the least energy input). This is because most of the heat from LEDs comes off their circuit board (backplane) where well-designed grow lights use heat sinks to efficiently dissipate it.

Brassica seedlings light intensity comparison

Light intensity is one of the most important measurements to know when comparing grow lights. Although, more light intensity is only better up to a point. Too much light intensity burns plant tissue as demonstrated in the experiment pictured on the right, comparing Brassica seedlings' responses to 2 light treatments: 350 and 1000 µmol m-2s-1

Key features that make LED Habitats work exceptionally well include:

  • It’s easy to adjust the height of the grow light so that it can be kept close (2-3”) from the top-most leaves of your plants.
  • The light output is intense throughout the footprint, which is the entire area beneath the LED light array (contained in the dome).

LED chip quality effects the quality of LED grow lightsLED chip quality

Quality diode manufacturing comes at a price. Each diode must be manufactured according to accurate specifications to emit the correct wavelengths and maintain its integrity over time. “Light Emitting Diodes are made from exotic semiconductor compounds such as Gallium Arsenide (GaAs), Gallium Phosphide (GaP), Gallium Arsenide Phosphide (GaAsP), Silicon Carbide (SiC) or Gallium Indium Nitride (GaInN) all mixed together at different ratios to produce a distinct wavelength of color (source: http://www.electronics-tutorials.ws/diode/diode_8.html ).”

Each diode must be manufactured according to accurate specifications to emit the correct wavelengths and maintain its integrity over time. Each diode must be manufactured according to accurate specifications to emit the correct wavelengths and maintain its integrity over time.

As you can imagine, there are reputable manufacturers who use sophisticated technological processes to assure the diodes they produce emit the correct light wavelengths and are highly durable electronic components. On the other hand, there are a plethora of cheaply produced LEDs that aim to attract budget-conscious shoppers who may be unaware that differences exist in LED’s quality. Cheap LEDs may or may not emit the wavelengths that our plants need, and their emitted light intensity can also change in wavelength and/or decline within weeks or months after use begins and the diodes heat.

In all types of lights, the quantity of light emitted (measured in lumens or PAR photon irradiance) decreases with use. Traditional incandescent light bulb output diminishes much more rapidly than LEDs. Well-designed LED luminaires can retain 70% of their initial output for 50,000 hours or more, depending on operating conditions and other factors. (source: IES)

Our LED engines use only components from reputable, top-of-the-line manufacturers. We use high performance Cree LEDs because we know that quality in LED technology is definitely worth the price.

Lenses make a difference in LED grow lightsLED lenses make a big difference in light output and footprint

Light Emitting Diodes are essentially electrical transformers constructed and then encased in a transparent, hard plastic epoxy resin that protects the LED and also acts like a lens.

led-components See more in "Bonds, Bands, and Doping: How Do LEDs Work?" by Casiday & Frey

Depending on how the lens is manufactured, it may focus or spread light from the diode. Some types of lenses concentrate the emitted light directly beneath the LED chip, while others use reflectors and diffusers to extend the light to a wider area. Specialized manufacture of the LED lens, or the addition of a secondary lens can be used to spread light across the lamp’s intended growing surface area or "footprint." Comparing how grow light manufacturers use lenses can be challenging because, unfortunately, “there is no single metric that can fully describe the optical performance of a given lens (Digi-Key, 2016).

If lenses are used to extend the illuminated footprint of a grow light, they typically reduce efficiency (Digi-Key, 2016). Sometimes, you’ll see this in grow lights where LEDs are mounted in a single row. Although a reflector-type lens in an LED chip spreads the emitted light more widely, the result can be that the larger area receives a lower “light density”. Think of it like cutting a cake into smaller pieces to serve more people. Everyone gets cake, but they get less than if it were divided among fewer people.

Alternatively, multiple LED chips with lenses that concentrate emitted light beneath the chip can be mounted in a shared board to create an LED engine. With this design, the light density beneath the individual LED chips is maximized, and a custom light array—comprised of specific color LEDs—can be engineered. The illuminated footprint becomes the area directly below the LED engine.

At LED Habitats LLC, we work exclusively with a component manufacturer who consistently delivers LEDs with a strong combination of efficiency and beam control, so that we can produce a custom, durable LED engine with high performance and reliable output throughout its footprint.

Cooling fans can be noisy in LED grow lightsAre you a fan of noisy fans?

While LEDs use energy from electricity extremely efficiently, they do generate heat while emitting light. However, unlike traditional grow lights, well-engineered LED grow lights that are powered (driven) properly and constructed with high-quality components run so cool that plant tissue (leaves) can get very close the LED chips without harm. High-quality LED chips are mounted in heat-dissipating substrates, and those can then be mounted in larger heat sinks that cool with remarkable efficiency.

If the heat generated by LEDs is not dissipated, the lifespan of the LED chips is reduced and/or the chips may fail. There are two key ways that LED lights are manufactured to dissipate heat:

  1. LEDs are mounted in materials that transfer heat away from the diode
  2. LED chips mounted into a heat sink

When LED grow lights are designed, the engineer determines what heat sink is appropriate to use based on the LED mounting materials and other design requirements such as light enclosures, lamp materials, budget considerations, etc. As you might imagine, the materials for highly efficient thermal sinks are more expensive to manufacture.

fansSo, another solution used by LED grow light manufacturers are cooling fans that run whenever the light is on. That's fine if you don't mind the constant droning of a fan as background noise or if you're growing far from your living space. But what fun is that?

Another factor that affects LED chip temperatures (and lifespan) is how the chips are powered. Electricity must be delivered to the LED, and this is typically done with a “driver” that sends constant voltage to the diodes. LED chips are rated for specific power levels, so it is critical that the right match between drivers and LEDs be engineered. “Too much current and voltage can damage the light-emitting junction of the LED diode,” explains Domitrovich in the International Association of Electrical Inspectors Magazine, April-May 2014.

Though LEDs are rated to shine for 50,000 hours, in cheaply built grow lights with poor cooling or over-powered LEDs, the light intensity can drop significantly with normal use in a few months. This is really important for plants that depend on high intensity light for photosynthesis, growth, and flower development.

LED-Habitat-420

LED Habitats are built with sophisticated heat sinks that cool super-efficiently without any cooling fan, so all Habitat LED grow lights run silently. They were also designed with high-end LEDs that are driven at less than 50% of their capacity to extend their useful life to the maximum. The result is a highly efficient LED grow light that can live in any room with you for a very long time and not drive you crazy with a loud cooling fan that runs whenever it’s turned on.

 

Choosing the right LED grow lightsAre you ready to choose an LED grow light, now? I hope the information presented here helps you appreciate that choosing an LED Habitat means that you’re choosing an extremely well-engineered LED grow light –built to last and grow plants exceptionally well.

We’re so confident in the durability of our Habitats and how much you’ll love owning one that we guarantee satisfaction and include a limited 90-day warranty on all components. In addition, if you succeed in wearing out the LED engine in your Habitat after using it for 50,000 hours, please contact us, and we’ll help you exchange your LED Habitat engine for just the cost of the components plus shipping. Our goal is to keep you growing strong!

--Hedi

Special thanks to Dr. Robert Morrow for taking the time to review this blog post and suggest additional relevant and current research and publications.


Resources cited in this blog and recommended for more information

There are many sources with more in-depth information about LED light components and measuring LED light inputs and outputs, but I caution you to critique their origins and rely on reputable sources only. I’ve been amazed by the amount of misinformation and pseudoscience about this subject that is published online by hobbyists and businesses. I recommend the following resources:

Some of the most current and in-depth work on understanding LED efficiency and their use in growing plants comes from Dr. Bruce Bugsby at Utah State University. He and his student, Jacob Nelson, published in 2014 the results of their study, comparing lighting options for horticulture (http://www.cpl.usu.edu/htm/publications/publication=15594)

A new look at classifying and labeling electric lights in horticulture—particularly LED grow lamps—written by Dr. A.J. Both and colleagues: Proposed Product Label for Electric Lamps Used in Horticulture and Plant Biology. This will be coming out later in 2017 in the HortTechnology Journal.

An updated look at LEDs in horticulture: Mitchell, C.A., M. P. Dzakovich, C. Gomez, R. Lopez, J. F. Burr, R. Hernandez, C. Kubota, C.J. Curry, Q. Meng, E.S. Runkle, C.M. Bourget, R.C. Morrow, and A.J. Both.  Light-emitting diodes in horticulture.  In: J. Janick (ed) Horticultural Reviews Volume 43: 1-87.

Phillip Davis’ Technical Guide called Lighting: The principles, available free online http://horticulture.ahdb.org.uk/sites/default/files/u3089/Lighting_The-principles.pdf

Cooper’s informative 2007 article in LEDs Magazine: http://www.ledsmagazine.com/articles/print/volume-4/issue-8/features/driving-led-lamps-some-simple-design-guidelines.html

Articles published online by Apogee Instruments, a well-reputed instrumentation manufacturer. This one discusses in detail the various ways of measuring output from LEDs: http://www.apogeeinstruments.com/light-intensity-measurements-for-light-emitting-diodes-leds/ )

Digi-Key, 2016 http://www.digikey.com/en/articles/techzone/2016/dec/choosing-lenses-to-make-the-most-of-led-lumens

Domitrovich’s article, A Look at Solid State Lighting in the International Association of Electrical Inspectors Magazine, March-April 2014. http://iaeimagazine.org/magazine/2014/03/04/a-look-at-solid-state-lighting/

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