Should I Use HPS or LED for Growing Licensed Cannabis?

“What lighting source should I use for my licensed cannabis grow?” and “I am comparing LED to HPS, which do you recommend?” are two of the questions the team at P.L. Light Systems is asked most often.

There is no single answer, and anyone who gives you one before asking about your building, your climate, and your cultivar list is selling rather than advising. P.L. Light Systems sells both LED and HPS, which means this article has nothing to gain from steering you toward either. Here is the short version, then the six factors that decide it, then how to read the comparisons you are handed.

LED, HPS, or Hybrid at a Glance

The table is directional. Which column wins is decided by the six factors below, ranked against your own operation, and confirmed by a light plan for your facility.

The Six Factors That Decide It

Rate these in the order that matters to your operation, because very few facilities get to optimize all six. The ranking is the decision. Cultivar runs through several of them rather than sitting as a factor of its own, since it drives the spectrum you want and the growing practices around it more than it drives the technology itself.

1. Budget

An LED system costs more up front than a double-ended HPS system covering the same footprint. Two things narrow the gap.

The first is rebates. LED fixtures carrying a DLC Horticultural listing are eligible for consideration by many utility and energy-authority incentive programs across North America, and every P.L. Light Systems LED fixture carries a listing. Listings are granted per model and spectrum, so confirm the exact configuration you are specifying before you file. Program terms for cannabis facilities vary by administrator, so ask the program directly whether the application has to be approved before the equipment is bought.

The second is service life. P.L. Light Systems warrants its LED luminaires for five years. On the HPS side, the luminaire and its electronic ballast are warranted for forty months, and double-ended HPS lamps for four years or 10,000 burning hours, whichever comes first. Those terms apply to factory-standard configurations, and the difference changes the replacement cycle you are budgeting for. Ask for the warranty terms in writing on both sides of any comparison, including what photon flux maintenance is stated and over what period.

2. Maintenance

Both technologies need cleaning to hold their rated output, and neither is maintenance-free.

LED fixtures need the lenses cleaned annually for optimal performance. Follow the maintenance guidance for the fixture you own rather than whatever is on the shelf in the head house, because the optic is the part doing the work.

HPS fixtures need reflector cleaning on a similar cycle, plus re-lamping roughly every one to four years depending on burning hours. Both jobs carry labour, and re-lamping carries the lamps as well.

Per fixture the difference is small. Across a full facility it is a real annual line, and it belongs in the operating comparison rather than in a footnote.

3. Electrical Supply and Operating Cost

Start with supply capacity rather than fixture choice. Is there headroom in your existing service? Does the plan require a transformer to expand it? An incoming-supply upgrade can cost more than the difference between the two lighting systems, and for a lot of retrofits it settles the question on its own.

Then work the annual energy cost yourself, once per option:

(annual lighting hours x actual fixture wattage x number of fixtures) / 1000 x your $/kWh

Use actual fixture wattage, not lamp wattage. A 1000W double-ended HPS fixture draws more than 1000W once ballast losses are counted, and using the lamp rating understates the HPS side. Run the formula against the fixture count each light plan returns.

For a sense of the gap between current fixtures, P.L. Light Systems plans the same greenhouse both ways in its own ROI guide. The 1000W NXT2 HPS luminaire delivers 1978 µmol/s while drawing 1045W, which works out at 1.89 µmol/J. The 750W ParFX Ultra delivers 2849 µmol/s while drawing 744W, which is 3.83 µmol/J. Delivering the same light to the same canopy, the HPS layout draws roughly twice the electricity of the LED one. Both figures come from the same published plan, so the comparison is like for like rather than a modern LED measured against end-of-life HPS. On a retrofit, that count usually carries across from the HPS layout already in the building, and the light plan is what confirms it.

4. HVAC Requirements

Indoor facilities and greenhouses pull in opposite directions here, which is why a single answer to the LED question does not exist.

Indoor

Cooling is one of the highest production costs in the building, and the air conditioning load follows the heat the fixtures make. One watt equals 3.412 BTU per hour, so the number of fixtures x actual fixture wattage x 3.412 gives the BTU/h load. Run it for each light plan. A lower connected load per unit of delivered light is a direct reduction in the cooling equipment you buy and then run for the life of the operation.

Greenhouse

The same radiant heat is doing useful work through a Canadian winter. Heat the fixtures no longer supply has to come from the heating system instead, so part of the electricity saved comes back as fuel. That does not make LED the wrong answer. It makes the heating change a line in the calculation instead of an omission, and it is usually large enough to matter to the payback.

5. Growing Practices

Facility layout constrains the fixture before spectrum does.

Vertical Racking

Additional tiers add canopy within the same footprint. LED suits close-to-canopy mounting because of its lower radiant heat, and that is what makes tight tier spacing possible at all. Expect yield per tier to run below the ground tier, since the plants are smaller, and expect each tier to behave as its own microclimate. The HVAC design gets harder, not just bigger.

Single Layer

Mounting height and the distance available above the canopy decide what fits. HPS luminaires need clearance, typically at least three feet from the canopy. Where the available height is below that, the decision has been made for you.

6. Spectrum

LED lets you select, and in some fixtures tune, the spectrum, which opens up effects on morphology and metabolic processes that a fixed source cannot reach. It also brings a learning curve and a rebalancing of temperature, CO2, irrigation, fertigation, and often humidity, because the crop transpires differently under it.

HPS gives you one fixed spectrum, thoroughly understood, with a long record of grower experience behind the results and no learning curve to fund.

Spectral flexibility is only worth paying for if you have the appetite and the record-keeping to use it. If nobody in the building is going to run the trials, you are buying a capability you will not exercise.

What Growers and Researchers Broadly Agree On

Most growers agree on two points. Young plants and the vegetative stage do better under a source with a meaningful blue or full-spectrum white component, largely because it limits internode stretch and produces a stockier plant. Flowering responds well to a source weighted toward red.

Past that, the ground gets soft. Growers experimenting with added blue late in flower have reported higher terpene and cannabinoid levels, and the reported figures vary so widely that the only honest summary is that it depends on the cultivar. Michael Dixon, Director of Environmental Control Research at the University of Guelph, quoted by HortiDaily in 2017, put it plainly: “We have found that the optimal LED spectral recipe changes with every strain of cannabis.”

That is the practical problem in one sentence. Cannabis cultivars descend from populations that evolved under very different light across very different latitudes, and they do not respond alike. If you run a single cultivar for the life of the facility, a tuned recipe is worth chasing. If you run six and rotate them, a recipe tuned to one is a compromise for the rest.

So no supplier can hand you a proven optimum spectral recipe for cannabis, because a recipe that works is tied to the cultivar it was tuned on. Treat a supplier who offers one universal recipe as a supplier making a sales argument, and ask what the ROI is on the spectral difference being sold. If the gain is a few percent of cannabinoid content, it still has to clear the cost of the equipment delivering it.

Greenhouse and Indoor Facilities Ask Different Questions

In a greenhouse, sunlight already delivers the full spectrum and the supplemental fixtures are topping up intensity and daylength. The spectral argument for LED weakens accordingly, and the decision comes down mainly to energy cost, heat, and capital. That is not the framing an LED-only supplier will offer.

Indoors, the fixture is the entire light environment. Spectrum choice carries real weight, and so does every watt of heat, since a sealed facility manages it mechanically rather than by venting.

Retrofitting LED Into a Facility That Already Runs HPS

Our LED fixtures are engineered to accommodate a one-for-one retrofit from an existing HPS system, so the mounting positions, spacing, and structure already in the building can usually be reused. That matters well beyond the fixtures, because added track, truss, and wiring are what turn a lighting purchase into a construction project.

The layout still gets modelled before anyone quotes it. Our guide to the ROI of an LED retrofit works through the budgeting side of the same decision. Mounting height, target DLI, and the crop plan decide the final specification, and the light plan is what confirms fixture count, spacing, and connected load.

Canopy Penetration and Mounting Distance

The reason some growers still say LED is not ready for commercial cannabis has less to do with the diodes than with mounting geometry.

A fixture with a wide distribution mounted well above the canopy also lights the crop from several rows over, and that crossover puts light into the canopy from angles the top leaves are not shading. A fixture hung nine to twelve inches off the crop trades most of that crossover for tier spacing, and the shadow cast by the top layer hardens as the source gets closer. Hold a flashlight over your hand and watch the shadow grow as the light gets closer.

None of that is a verdict on a technology. Close mounting is the right trade in a racked room, where the tier spacing is the whole point, and the wrong one in a single-layer operation with height available. LED fixtures built for truss mounting hold a working distance between fixture and canopy, and that is what made the technology usable in commercial rooms in the first place. The light plan is what settles the trade for your unique grow operation.

Where a Hybrid LED and HPS System Fits

A full conversion is not the only path, and we cover the approach in more depth in HPS or LED? Why Not Both with a Hybrid Lighting System. A hybrid layout keeps a portion of the HPS fixtures and adds LED alongside them.

It preserves radiant heat through the coldest months, gives the grower the option of running the LED side alone as daylight hours extend in spring, and spreads the capital cost over a longer window. Because it reuses existing infrastructure, the incremental spend is lower than a full conversion.

For cannabis there is a second reason. A hybrid facility lets a grower learn how their cultivars respond to LED on part of the crop before committing the whole facility to a spectrum, which is worth more than it sounds when the optimum recipe is cultivar-specific.

Where LED Versus HPS Comparisons Go Wrong

Comparisons are often published by a manufacturer that sells only one of the two technologies, and the same three levers get pulled on both sides.

The HPS Baseline

Photosynthetic efficacy is stated in micromoles per joule: photon output divided by fixture wattage. It is arithmetic you can do yourself, and that is the point, because the result depends entirely on which HPS fixture goes into it.

An old single-ended screw-in lamp, or an end-of-life output figure, produces a much lower HPS number than a current double-ended electronic fixture, and the LED payback improves in proportion. A current 1000W NXT2 delivering 1978 µmol/s at 1045W sits at 1.89 µmol/J. Comparisons built on 1.85, or on the 1.7 that represents an old lamp at end of life, are describing equipment most commercial growers are not running. Ask which HPS fixture and which lamp age the savings figure assumes. If the answer is vague, the payback is not a number you can budget against.

The Trial Design

Check how a trial was run before you act on its result. Some cannabis lighting comparisons grow each crop under a single source from propagation through harvest. That design compares whole production recipes, not flowering spectra. Plants that spent their vegetative stage under a source poorly suited to it enter flower already stretched and behind, and no result from the flowering stage separates that starting handicap from the spectrum being tested.

A trial worth acting on runs a common propagation and veg protocol and changes only the flowering treatment.

The Light Plan

Fixture-to-fixture output tells you very little. A reading taken directly beneath a single fixture says nothing about what the canopy between fixtures receives, whichever technology produced it.

What you need is a light plan for the whole installation zone, stating the average light level in micromoles and the average uniformity across the canopy, with a uniformity target above 90%. Ask for one from each technology at the same target light level. Uneven light is not a cosmetic problem in cannabis: hot spots and dark spots transpire, drink, and take up nutrients at different rates, and the facility ends up managed to an average that suits neither. A supplier who cannot produce those plans is not one to shortlist.

What to Ask Before You Sign

• Will you produce a complete light plan for both technologies at the same target light level, with average micromoles and average uniformity for each?
• Which HPS fixture and which lamp age does your energy-savings figure assume?
• Is the LED fixture DLC Horticultural listed in the exact model and spectrum I am specifying, and which rebate programs does that make it eligible to be considered for?
• What does the warranty cover, and what photon flux maintenance is guaranteed over what period?
• What happens to my heating and cooling load, and is that change inside the payback calculation?
• Do you sell both technologies, or only the one you are recommending?

Frequently Asked Questions

Is LED or HPS Better for Growing Cannabis?

Neither is better in general. The answer comes from ranking six factors against your own operation: budget, maintenance, electrical supply and operating cost, HVAC, growing practices, and spectrum. An indoor facility fighting its cooling load and a greenhouse relying on radiant heat through winter reach opposite conclusions from the same facts.

Can LED Replace My HPS Fixtures One for One?

Yes. P.L. Light Systems LED fixtures are engineered to accommodate a one-for-one retrofit from an existing HPS system, so the mounting positions and spacing already in the structure can usually be reused. The existing layout is still modelled first, and the light plan confirms fixture count, spacing, and connected load before a quote.

Does LED Increase THC and Terpene Levels?

Growers experimenting with added blue light late in flower have reported higher terpene and cannabinoid levels, and the reported size of the effect varies by cultivar. Michael Dixon of the University of Guelph, quoted by HortiDaily in 2017, said the optimal LED spectral recipe changes with every strain of cannabis, so any single figure quoted for you was measured on somebody else’s genetics.

Do I Need a Different Spectrum for Veg and Flower?

The long-standing indoor recipe is more blue or full-spectrum white through propagation and veg to limit stretch, then a source weighted toward red into flower. It remains a sound starting point.

How Much Cooling Does LED Save Compared With HPS?

Calculate it rather than accepting a percentage. One watt equals 3.412 BTU per hour, so the number of fixtures multiplied by actual fixture wattage multiplied by 3.412 gives the BTU/h load. Run it against the fixture count in each light plan and compare the two results.

Where the heat goes matters as much as how much of it there is. Roughly 55% of an HPS luminaire’s energy leaves as radiant heat aimed at the crop, against roughly 15% for LED, which moves more of its heat by convection into the air where the ventilation system handles it. We break that down further in how LED and HPS lighting affects air and leaf temperature. That is why the same connected load feels cooler at canopy level under LED, and why a cold-climate greenhouse can miss the radiant heat it used to get for free.

Is a Hybrid LED and HPS System Worth It?

Often, in greenhouses in cold climates that depend on radiant heat through winter, and for operations that want to limit up-front capital or trial LED on part of the crop before converting the whole facility.

Does the Spectrum Argument Still Apply in a Greenhouse?

Less than indoors. Sunlight is already supplying the full spectrum, so supplemental lighting is mainly adding intensity and daylength, and the greenhouse decision turns on energy cost, heat, and capital instead.

We model your facility under LED and HPS before you choose

The comparison only means something once your building, your energy rate, your climate, and your cultivar list are in it. Our team will model your facility under both LED and HPS at the same target light level and return fixture count, spacing, connected load, and uniformity for each, so you can compare like for like and decide on your own numbers.