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The Truth About LED and HPS Lighting for Cannabis

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Are LEDs right for you? Learn the difference between LEDs and HPS for your grow.

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When is the Right Time to Switch from HPS to LEDs for Cannabis?

In recent years, light-emitting diodes, or LEDs for short, have carved out their place in the cannabis lighting world — and given rise to a lot of questions. Can LEDs produce the same high-quality flower as high-pressure sodium (HPS) lamps? Will they save you money? And what are the drawbacks of LEDs that companies aren’t telling you?

HPS lights have long been the industry standard. And as the saying goes, “if it isn’t broken, don’t fix it.” It’s true; there’s nothing wrong with high-intensity discharge (HID) technologies like HPS. In fact, HID lamps might be best for your application and budget.

But, if you’re reading this, you’re probably ready to tap the benefits of LEDs — benefits which include increased efficiency, cost savings, higher light intensity, and a level of control over the lighting spectrum that’s impossible with HPS. Even better, LEDs can give you an overall healthier plant. So, let’s take a look at the two technologies to see which is right for you.

Comparing LEDs and HPS Lighting for Cannabis

Generalizations about LEDs — or HPS lamps, for that matter — lead to some bad conclusions. With horticultural lighting, it’s all too easy to make apples-to-oranges comparisons. That’s why many growers have had disappointing experiences with LEDs in the early years.

LEDs have varying efficiency ratings, depending on the product, and that dramatically affects how much light they’re producing. It’s the same with HPS. When we talk about HPS technologies in general, we gloss over important design elements like (1) the wattage of the fixture, (2) whether the lamp is single- or double-ended, and (3) whether the ballast is magnetic or electronic, etc. 

For instance, an HPS fixture may achieve an efficiency of 1.7 µmol/joule if it’s a double-ended lamp with a 1000-watt electronic ballast. But a different, 400-watt HPS light with a magnetic ballast is a different story. The 400-watt will only score an efficiency rating in the 1.0-µmol/joule range. Essentially, we’re talking about different technologies and calling them both “HPS.” 

LEDs are much the same. Though they’re generally more efficient than HPS (with some clocking 2.8 µmol/joule), some LEDs are less efficient than high-quality HPS fixtures, and they give you less light. You’ll find the LED fixtures vary in efficiency based on (1) the type of diodes, (2) the color composition of the spectrum, (3) the product’s overall quality, and other engineering factors. What’s more, even if the µmol/joule efficiency is high, an LED fixture may not have the spectrum to give your plants good morphology, as explained below.

You may also find some hidden inefficiencies lurking in the ballasts of HID fixtures. All too often, the µmol/joule rating on HPS products states the lamp efficiency, not the actual product efficiency. The lamp may perform well in a laboratory setting based on the wattage provided, but when the electrical loss of the ballast is factored in, the efficiency numbers begin to look very different. The reflector hood also decreases the stated efficiency of an HPS fixture.

In truth, efficiency goes beyond electrical consumption. Well-engineered lighting products will provide you with better harvest outcomes for several reasons. For instance, when you give your plants a balanced, fine-tuned spectrum, you can expect an increase in secondary metabolites and larger crops of denser flowers. And electrical efficiency means lower heat, which creates a cascade of cost-reductions due to reduced HVAC use, fewer circulating fans, and easier pest management.

Re-envisioning the HPS Spectrum with LEDs

LEDs have thrust the concept of the spectrum to the forefront of horticultural thought. That’s because they have the ability to precisely recreate individual colors of sunlight for research purposes — or to coax desirable traits from commercial crops. You may also hear colors of light referred to as wavelengths because each color has its own frequency, as measured in nanometers (nm). Blue light has a short wavelength of about 440 nm, while red light, at the opposite end of the spectrum, has wavelengths approaching 700 nm. 

Savvy growers have always used spectrum control to craft better cannabis. The standard protocol has been to switch from a cool-colored metal-halide (MH) spectrum for vegetative growth to a warm-colored HPS spectrum for flowering. The MH spectrum contains plenty of blue light, which is critical for avoiding extension growth and increasing leafing; the HPS spectrum is red-dominant, making it perfect for flowering. But neither HPS nor MH could recreate sunlight, and their spectrums couldn’t be modified because the gases in their lamps determined their color.

Yet LEDs can reproduce both these HID spectrums and more. Though LEDs could theoretically create any spectrum, early LED designs abandoned what worked for HID lights in favor of polarized blue/red spectrums. And some of those designs persist to this day. It’s true that plants have a strong photosynthetic response to blue and red light, but such extreme spectral designs completely neglect the middle wavelengths of green and yellow. Many of the manufacturers of these so-called “purple” LEDs claimed to have magic spectrums for quality cannabis flower. But, actually, the incomplete spectrums typically yield disappointing harvests, particularly at lower light intensities.

Now, LED fixtures are engineered to contain all the spectra needed throughout the growing cycle, and spectrum manipulation is less extreme. You may see lights that have a mildly purple-ish appearance — such as the Heliospectra ELIXIA series — yet those fixtures actually include sufficient green and yellow light to fulfill all of your plants’ needs. To see the spectrum that a light is truly producing, it’s critical to reference the accompanying spectrum chart. The colored curve you’ll find there will show if the middle wavelengths of green and yellow are present — or lacking.

Moreover, modern LED spectrums eliminate the need to change from HPS to MH mid-crop cycle, and some fixtures offer tunability. Tunable fixtures enable growers to subtly change the colors and ratios of color in their spectrums throughout the growing day or season.

The Pros (and Cons) of LEDs for Cannabis

LED Pro: Higher Efficiency

LEDs are far more efficient than HID lighting. Pound-for-pound — or rather kilowatt-for-kilowatt — they produce more light than HPS fixtures. The diodes of an LED fixture are inherently superior at converting electricity into light. That means you’ll have a lower electrical bill and you might not need as many fixtures to provide the same amount of light.

Along with better electrical efficiency comes better efficacy. A tailored LED spectrum provides plants with what they need for increased growth on a per-kilowatt basis. With an optimized spectrum and strong light intensity, plants yield more salable material, which fetches higher prices because of its enhanced quality.

LED’s lower electrical consumption reduces carbon emissions too. This environmental benefit has prompted many governments to offer a rebate credit for switching to LEDs, so check with your local jurisdiction.

LED Pro: Reduced HVAC Requirements

Because LEDs create much less heat than HPS, air-conditioning costs fall by as much as 30-40 percent when you make the switch. If you’re designing a facility from the ground up, your designer can specify a smaller HVAC system, thus lowering your capital expenditures. 

Unlike HPS, the LED spectrum does not contain infrared light. Infrared, which is radiant heat, increases leaf temperature. With a lower temperature at the leaves, you can run higher room temperatures for a significant savings in HVAC costs. Lower leaf temperatures can help mitigate pests and mold, too.

LED Pro: Longevity and Low Maintenance

Unlike HID, LEDs won’t need replacement every three or four crops, and they aren’t susceptible to breakage. HID bulbs are delicate, and as growers know, they need to be handled with the utmost care to avoid costly breakage. The possibility of breakage — and the resulting release of metallic gases such as mercury — may violate European Good Manufacturing Practices and other standards. If you want to properly dispose of these lamps, you’ll need to work with — and pay — a specialized recycling facilitator.

LEDs, on the other hand, have exceptional durability and runtimes. Once hanging, LED fixtures provide 50,000 hours of runtime and frequently go for ten years before needing replacement. IP-rated waterproof fixtures are easy to clean, and the individual diodes are encased in polymer — not glass — which makes them the most durable lighting solution available today. If your fixtures have an IP-67 rating, you can spray them with a hose between production cycles. 

LED Pro: Vertical Growing and Dimmability

Because LEDs have very little infrared in their spectrum, they can be hung close to the crop, which opens the door for vertical cultivation and lets you make the most of your square footage. Multiple LED light bars can be placed across the crop without the hotspot characteristic of HID technologies. And unlike HPS lights, LEDs are dimmable without a loss in efficiency, which means you can slowly increase your light intensity throughout the crop cycle while staying cost-effective.

LED Con: Higher Upfront Costs

Prospective buyers of LED lights may encounter sticker shock if they’re only familiar with HID lamps. The manufacturing processes and materials needed to create LED fixtures simply come at higher costs than those used for HID lamps. Despite lower lifetime costs, LED fixtures cost more than HPS upfront. For some growers, this makes LEDs a no-go, even though the longer runtimes and ease-of-use features payoff the investment several times over.

LED Con: Light Spacing

Light from LEDs typically has a tight footprint similar to a spotlight. The beam angle of HPS lights, by comparison, is broad, which makes them easier to space in a greenhouse. Though the tight footprint of an LED light is great for narrow tables, overlapping the illumination area can be tricky, especially in greenhouses. Secondary optics (i.e., a lens plate over the diode array) can evenly distribute photons and ensure light uniformity over a broader area.

LED fixtures vary in terms of their beam angles, so it’s important to understand how they provide light for your plants. For large installations, make sure you work with an LED company that has a qualified lighting designer. 

LED Con: Changes to the Dehumidification Plan 

Growing with LEDs is different. LED lights lower the cooling load in the grow room while increasing the dehumidifcation needs. That’s because the room is naturally cooler with LEDs, yet photosynthesis — and evapotranspiration — remain about the same. Plant’s still transpire because the stomata are open for CO2 exchange, and they still release moisture into the air.

Your first crop with LEDs may entail some unexpected humidity levels. Relative humidity increases as the temperature drops, so more dehumidification may be necessary. Make sure to keep an eye on your relative humidity and vapor pressure deficit throughout the crop cycle.

When to Invest in LEDs? Experts Say “Yesterday”

Horticultural LEDs have steadily increased in efficiency over the years, while simultaneously dropping in price. That’s left many growers waiting and waiting for the right time to switch. But experts say the time is now. Or, rather, years ago.

In 2017, a group of prominent researchers — who include Bruce Bugbee, Ph.D., and Erik Runkle, Ph.D. — reviewed the efficiencies and costs of the lighting products on the market and came to a simple conclusion: it’s time to switch (1). Even as far back as 2017, changing from HPS lamps to LEDs reduced costs by as much as 50 percent and provided a payback time of just two to three years. Since then, LEDs have continued to increase in efficiency while decreasing in price. 

If you’re interested in learning more about how LEDs can help your organization become more efficient — while still maintaining high product quality — contact Heliospectra.

Heliospectra offers cultivators the best cannabis-optimized lights available today. At 2.8 µmol/joule, the MITRA LED fixture is exceptionally efficient and provides consistent high-quality light output. MITRA adapts to any growing environment by utilizing modular LED panels. The possible configurations can give you even light coverage across indoor growing beds or fit perfectly under Unistrut in a greenhouse. Or, you can arrange the MITRA modules in rows for vertical cultivation.

MITRA is available in three spectrum options for vegetative and reproductive growth, and broad-spectrum for general use. With MITRA, real-world growers have reported enhanced secondary metabolite production— with terpenes and cannabinoids increasing up to 30 percent over HID technologies.

To learn more about how MITRA can enhance your grow, get in touch with us.

References:

1. Runkle, E., Bugbee, B. Plant Lighting Efficiency and Efficacy: µmol·J–1 Greenhouse Product News. July 2017. https://www.canr.msu.edu/floriculture/uploads/files/lighting-efficacy.pdf

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