Seeing Double: Double-ended, High Pressure Sodium (HPS) Lighting

By Lee McCall
Published: April 19, 2017 | Last updated: April 20, 2017 03:38:59
Key Takeaways

This article focuses on one of the greatest and most recent advancements in horticultural lighting that is changing growers’ abilities for the better: double-ended, high pressure sodium lighting systems.

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Gardening indoors successfully is a composition of basic fundamentals. To garden indoors is to control and execute these fundamentals upon command. Because of amazing new technology, the productivity standards of indoor gardening have excelled in recent years.


Lighting, nutrients, temperature and humidity controllers, carbon dioxide enrichment and artisan growing mediums are now common tools that allow average growers to set higher standards. This article focuses on one of the greatest and most recent advancements in horticultural lighting that is changing growers’ abilities for the better: double-ended, high pressure sodium lighting systems.

Grow lights are mandatory tools for indoor gardening that allow individuals to manipulate all phases of plant growth year round on a perpetual schedule without the use of sunlight. Many types of lighting technology boast similar yet different productivity standards. For example, light-emitting diode (LED) and plasma lighting systems continue to impress growers due to their low energy consumption.


High pressure sodium (HPS) and metal halide (MH) lights have helped shape the ways, methods and styles of how we cultivate plants today. The introduction of T5 fluorescent lighting also revolutionized the lighting market with energy efficiency, low heat emissions and high light output.

The T5 is an exceptional tool for vegetative production as the clean spectrums of various wavelengths in higher Kelvin temperature ranges produce stocky, tightly-noded plants.

New Double-ended High Pressure Sodium Lighting Systems

Now, double-ended HPS technology is making its presence known in the marketplace with proven high-quality results. This lamp technology has shown horticulturalists a new path to greater yields and quality. Double-ended HPS lights are now emerging from several reputable manufacturers in the hydroponics industry.


The effects on yields are exceptionally positive for what seems like 100 per cent of growers who try them. So, what makes these lights so special? For starters, these bulbs degrade slower than traditional, single-ended HPS bulbs. In fact, after 10,000 hours, double-ended lamps will still output approximately 90 per cent of their original intensity.

Next, the spectrum and relative energy measurement dictated in micromoles far surpasses that of the industry-standard high intensity discharge (HID) mogul technology. Micromoles is a term we are hearing more and more in our industry.


It’s a measurement that provides a comparative reference to understand what crops need in terms of light level requirements for particular crops and their various phases of growth. The double-ended HPS lamp has been recorded to produce more than 2,000 micromoles, whereas traditional mogul-based technology falls as low as 50 per cent less with identical variables.

Think of it this way: you’re using the same amount of energy to produce up to 50 per cent less usable light to your crop. In some cases, this variance is the difference of up to double the yield per lighting fixture replaced.

Aside from use during blooming, fruiting and flowering production, double-ended HPS lights work great for promoting vegetative growth as well. However, the concentrated wavelengths of lower nanometer range spectrum, a.k.a. red light, is favorable in blooming production areas.

In other words, these lights excel in bloom production scenarios. Double-ended HPS bulbs are more stable than traditional, single-ended HPS bulbs, and this allows them to have a 10 per cent increase in light intensity and PAR output over traditional single-ended HPS bulbs. Double-ended HPS bulbs also emit more UV and IR light than traditional bulbs.

Available in a variety of styles, from adjustable-wing style reflectors, to air-cooled models and non-air-cooled attached ballast models, there is a type of double-ended light to fit any growing scenario. Many growers claim one of the biggest benefits of double-ended lighting is larger footprints from the same energy consumption.

According to light level measurement devices, double-ended lights are brighter and can cover larger surface areas in comparison to standard 1,000W light systems. Higher ceilings are recommended for operating double-ended lights so larger footprints may be achieved, which could ultimately result in larger yields due to the increased growing area.

Open-hood, non-vented reflectors will emit more heat from the lamp than air-cooled models. Greater ceiling heights are required to avoid canopy burning and other phototoxic effects on the crop. These lights perform better at three to four feet from the canopy, rather than the standard one to two feet.

Of course, these distances are subjective dependent on environmental conditions, but keep in mind the higher the light, the bigger the footprint and the less hot-spot concentrations occur. As mentioned earlier, the reflector’s design will influence footprint and canopy coverage.

Some of the air-cooled, double-ended reflectors concentrate the light within a confined footprint directly under the light, while other open-hood style designs spread light for maximum distribution and even coverage. Consider these factors when purchasing a light system as they will affect the overall productivity in the growroom.

Aside from the distance between canopy and fixture, another question that always comes up for growers is, “How hot do these lights run?” In comparison to mogul or traditional HID lights, there is really no difference.

The same kWh (kilowatt hours) is still being consumed to operate both styles of lights; therefore, heat output is matched through watt to BTU produced. Air-cooled lighting is not applicable to this question as there are multiple factors that can determine the heat output when using air-cooling reflectors.

For example, a grower who uses 1,000 CFM of room temperature to cool eight 1,000W lights might have a different heat output compared to if they were using 1,000 CFM of air-conditioned air to cool the same set-up. Basically, for open-style reflectors with no air cooling, 2,000 to 4,000 BTU of air conditioning is recommended for every 1,000W light in the room.

HPS Increases Plant Yields

Now for the good stuff. Research shows that double-ended HPS lights are increasing yields by anywhere from 20, 30 and 50 per cent. Several reports from side-by-side grows have concluded up to double the yield when swapping a fixture for a fixture.

So, how is this possible, especially when using the same amount of input power? Well, as mentioned earlier, the increased micromole output per watt means that increased footprints are applicable. The industry standard 4x4 foot grid per 1,000W light is easily increased to 6x5 ft, and even greater in some cases.

Again, reflector design and style will influence the shape of the footprint produced. My recommendation is to implement the air conditioning and go with an open-hood design if the space permits. For basements and other low-ceiling scenarios, air-cooled models will suffice just fine.

In conclusion, new double-ended HPS lighting is taking over growrooms everywhere, and with good reason. The technology continues to amaze even the most seasoned and experienced growers. Try double-ended lighting in your growroom and increase your yields today.

Read More: Double-Ended Lighting Technology: Worth It?


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Written by Lee McCall

Profile Picture of Lee McCall
Lee McCall is an alumnus of Johnson & Wales University. His extensive culinary background helped him gain experience in and knowledge of fine dining and food production, which developed into a career in the hydroponics industry. Lee and his business partner use their Denver-based businesses to educate the public on sustainable gardening and high-quality produce.

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