One of the most common questions we get here at Garden Grove Organics is how light emitting diodes really stack up to traditional light sources like high pressure sodium or metal halide lamps. There are so many brands of horticultural LED fixtures available now that many customers just want to know which model is right for them.
Right now you might be saying, “I’ve tried LED and wasn’t happy with the yield.” The truth is all LEDs are not created equal, and there are many false claims made by manufacturers. We hope this guide will help clarify some of common misconceptions surrounding modern LED technology.
Cliff Notes / TLDR: If you don’t have time to read the whole article, the short version is that we love LEDs for all stages of plant growth. You can can find a carefully curated selection of high quality LED lighting here.
LEDs have taken over virtually every lighting market on the planet as the result of their high efficiency and long life compared to traditional lighting like HID lamps and fluorescent tubes. While those older technologies are capable of producing 50 to 100 lumens per watt, the best LEDs can produce over 200 lumens per watt. That allows homes and offices that switch to LED to save 75% or more in lighting costs.
While lumens measure the intensity of light as seen by humans, plants sense light differently, so they need their own unit. Micromoles (µmol) are the general unit of measure for photosynthetic light, the light plants are able to use. It is expressed in µmol/sec (the amount light produced from a source) or µmol/m2/sec (the total light hitting a given area). This might sound a little complicated, and it can be, but with a little basic understanding you’ll be in a much better position to navigate the vast sea of LED marketing.
Now that we’re speaking in terms a plant can understand, let’s see how some of the most common technologies compare:
The chart above shows typical power usage and light output statistics for some of the most common horticultural lighting technologies. You can see that a high performance LED uses less power and provides more light output than the best traditional lights available. You might also notice that many cheaper LED fixtures, what we call pizza box lights, are actually less efficient than CMH and DE HPS.
One thing to note is that these numbers are based on the efficiency of the complete fixture. Some manufacturers will boast the on-paper efficiency of their lamps or diodes, but the real world numbers are usually less impressive.
Choosing the right spectrum when it comes to plant lighting is important for several reasons. First, the overall spectrum of light directly determines the shape and growth characteristics of the plant, known as morphology. This spectrum-dependent relationship is called photomorphogenesis, and it is completely independent of photosynthesis, the process plants use to harvest energy from light.
One example of this phenomenon is the shade avoidance response. As a general rule, the red end of the visible light spectrum penetrates deeper into the plant canopy than the blue end of the spectrum. When plants receive a high ratio of far red (730nm) they sense that they are being shaded by taller plants. In response, they stretch out and elongate their stems and leaves, a process called etiolation. The resulting growth is typically weaker and less desirable. For this reason, we don’t recommend LEDs that incorporate added far red.
Another feature touted by many LED manufacturers is the addition of ultraviolet, or UV light. While UV light can have some interesting effects on oil production and color, the benefits are not consistent across the board, and UV-LED technology has a long way to go. For those who like to experiment, we recommend and sell specially tuned fluorescent tubes which emit high levels of UVA and UVB. Contact us for details.
Full-spectrum diodes use a special phosphor coating to produce a wide range of colors from a single component. This type of light appears white or yellow to the human eye, similar to the color of the sun. We prefer 4000K full spectrum LEDs for all stages of plant growth. This spectrum provides a balance of all visible colors for sturdy, compact growth, and it’s much easier to work under than purple LEDs and even HPS.
COBs and Strips and Quantum Boards, OH MY!
We’ve seen that LEDs can provide higher efficiency and a fuller spectrum of light compared to traditional technologies, but what about all the different flavors of LED out there? While the vast varieties can seem overwhelming, all LEDs are simple semiconductors that emit photons (light) when current passes through them.
Dual Inline Package (DIP) – These are the classic “clown nose” LEDs that have been commonplace since the 1980’s. They are often found in “pizza box” LED grow lights in 3- and 5-watt versions using computer fans to cool them. This older technology is cheap to produce, but the performance and life ratings aren’t well suited to the demands of horticultural lighting. Early products using DIP technology yielded poor results, and were responsible for giving LED grow lights a bad reputation.
Chip On Board (COB) – In chip on board technology semiconductors are mounted directly to a circuit board. This allows many individual low power diodes to be placed close together in a single package. The resulting component looks and acts like one big, bright diode. However, there are drawbacks to packing everything so closely. Heat is the enemy of light emitting diodes, and it can reduce efficiency and shorten lifespan if not removed properly. Some manufacturers use heat sinks and fans to remove heat, but those add to the cost, weight, and energy usage of the fixture.
Quantum Boards – Quantum boards are simply circuit boards densely populated with surface mounted LEDs (SMDs). These SMD-style diodes are some of the most efficient light sources available, capable of efficiencies well over 3 µmol/joule. Mounting these highly efficient diodes on metal-core circuit boards allows heat to be dissipated into the air naturally, eliminating the need for fans or heat sinks. In addition, the even spread of light sources provides extremely uniform photon delivery at the plant canopy. Some great examples of LED grow lights using quantum board technology include the NextLight Mega and HLG 550 V2 R-Spec.
LED Strips – LED strips or bars are like quantum boards, but arranged in long rows instead of squares or grids. These lights are similarly capable of ultra high efficiency and long life ratings, without the need for additional heat sinks or fans. What sets strip or bar lights apart from those using quantum boards is the pattern of light output. Strips of diodes placed at even intervals provide extremely even coverage at close range. That makes this type of grow light ideally suited to growing shorter plants in vertical racks. A great example is the Gavita 1700e, which can be found in vertical commercial grows around the world.