Switching a growing facility from high-pressure sodium (HPS) to LED is one of the largest capital decisions a CEA operation makes, and it is one that often gets decided on an incomplete number. Energy savings alone do not tell you whether a retrofit pays back, and neither does a fixture-to-fixture price comparison.
This guide covers what actually belongs in the calculation: rebates, fixture count, heat load, lifespan, and the cases where keeping some HPS in the growing area is still the better answer.
Start With What a Retrofit Actually Replaces
The first question growers ask is how many LED fixtures it takes to replace their existing HPS layout.
Our LED fixtures are engineered to accommodate a one-for-one retrofit from an existing HPS system, so in most cases the mounting positions, spacing, and structure already in the building can be reused. That matters to the budget well beyond the fixtures themselves, because added track and truss are what turn a lighting purchase into a construction project.
Electrical scope is separate, and it belongs in the budget on its own line. Confirm fixture input voltage against the service you already have, and have the connected load from the light plan checked against your branch circuits and breakers, because LED drivers draw far higher inrush at switch-on than their running current suggests. If the fixtures are dimmable, budget for the control method the light plan specifies, since wired dimming needs control cable run to each fixture and a wireless control layer does not.
The layout is still modelled before anyone quotes it. Mounting height, target DLI, and crop type decide the final specification, and the light plan is what confirms fixture count, spacing, and connected load. A supplier who will not model your existing layout before quoting is not giving you a number you can budget against.
The Four Numbers That Decide Payback
1. Rebates and Incentive Programs
Regional energy rebates are easy to leave out of a retrofit budget, and they are usually tied to the fixture carrying a DesignLights Consortium (DLC) Horticultural listing, which is the qualification North American utility rebate programs commonly check. Listings are granted per model and spectrum, so confirm the exact configuration you are specifying before you order.
Rebate value varies by utility and by year, and programs open and close on their own schedules. Talk to your energy provider and your sales manager before you commit to equipment. Many programs require written pre-approval before a purchase order is issued or a deposit is paid, and programs that do accept an application after installation set a filing window. Confirm which rule your utility applies before you order.
2. Efficacy, Measured the Same Way on Both Sides
Photosynthetic efficacy describes how efficiently a fixture converts electricity into PAR photons, measured in micromoles per joule.
There is no single baseline that suits every project, and the right one depends on the decision in front of you. For a retrofit it is the equipment running in your facility today, at its actual ballast type, lamp age, and metered load, because that is what the new system displaces and where the saving comes from. A grower on older magnetic-ballast fixtures who benchmarks against new double-ended electronic HPS will understate the saving and make the payback look longer than it really is.
Where the choice is genuinely between buying new HPS and buying new LED, current double-ended electronic HPS is the comparison to use, rather than the least efficient example available.
Growers weighing one LED system against another are making a different comparison again, and there the figures only mean something if both sides are measured the same way. Ask whether a quoted micromoles per joule figure covers the whole luminaire at its rated input, and ask what photon flux maintenance the fixture is rated for, which is the number of hours until output has declined to a stated percentage of its initial value. That is a projection from test data rather than a warranted output level.
Ask any supplier which baseline their savings figure assumes. If they cannot tell you, the payback number is not one you can rely on.
3. Heat, and What It Costs to Replace
HPS fixtures put out radiant heat, and in northern growing regions that heat is doing real work through the winter. Growers who remove it entirely often find that a share of the electricity they saved comes back as natural gas.
An LED system delivers the same light at a lower connected load, so the heat load in the growing area falls roughly in proportion to the watts you remove, and much less of what remains arrives as radiant heat on the leaf. That is an advantage in an indoor facility fighting its cooling load and a cost in a greenhouse relying on that warmth in January. Neither is universally better. What matters is that the heating and cooling change lands in the ROI calculation instead of being left out of it, because it is frequently large enough to move the payback period materially.
The same shift touches irrigation and nutrition. Growers commonly water less under LEDs because the crop transpires less. Lower transpiration also slows calcium movement into new growth, which is the mechanism behind tipburn in leafy crops, and increasing air movement over the canopy is the usual response. Re-tune the climate to the crop with your own agronomist rather than carrying the previous recipe across, monitor root-zone EC, and scout regularly through the first cycle.
4. Lifespan and Maintenance
LED fixtures carry substantially longer service life than HPS lamps, which removes the re-lamping cycle HPS facilities budget for. It does not remove maintenance cost from the model. Drivers are the most common failure point on any LED luminaire, and photon output declines over the fixture’s life, so put the warranty term, driver coverage, and rated photon flux maintenance into the calculation rather than assuming zero.
They are not maintenance-free in service either. Dust and film on the lens reduce output the same way a dirty reflector does, and both belong on the same maintenance schedule. Turn off and lock out the branch circuit and let the luminaires cool completely before any of it, then follow our guide to cleaning horticultural luminaires for the lens and reflector procedures. Never use commercial cleaning products, soaps, or detergents on the lens. Build it into the maintenance routine so output lost to soiling does not get mistaken for the fixture wearing out.
Where a Hybrid LED and HPS System Still Makes Sense
A full LED conversion is not the only path, and for some operations it is not the best one.
A hybrid layout adds LEDs alongside a portion of the HPS fixtures already in the greenhouse. It preserves the radiant heat through the coldest months, lets a grower run LEDs only as daylight hours extend in spring, and spreads the capital cost across a longer window. Because only a portion of the growing area is converted at a time, the upfront spend is lower than doing the whole facility in one purchase, though the energy saving scales down with it, so phasing changes the cash-flow profile rather than shortening the payback period.
This is a common answer for vine crops, cannabis, and ornamental production in cold climates, where the winter heat contribution is not incidental.
Retrofitting a Research Facility
Research greenhouses face a version of this decision with an added constraint. Commercial adoption of LED has moved quickly, which can leave a research facility running trials under lighting the industry it serves has already moved past.
There is also a parts question. Ballasts, capacitors, and ignitors for models no longer in production are supported case by case rather than off a shelf, so confirm parts support for your specific fixtures with your regional sales manager before deferring an upgrade.
For research applications the spectrum has to be specified and held constant, because it is often the variable under test rather than a settled choice. As a general starting point, a red, white, and blue recipe suits greenhouse work where daylight fills in the gaps, and a broad-spectrum white suits sole-source indoor rooms. Specific trials will have their own requirements.
What to Ask Before You Sign
- Will you model my existing layout and return fixture count, spacing, and connected load before quoting?
- What baseline does your energy-savings figure assume, my current equipment or a new system?
- Is the fixture DLC Horticultural listed, and which rebate programs is it eligible for?
- What input voltage do these fixtures need, and what work do my existing circuits and breakers require?
- What does the warranty cover and for how long, and what photon flux maintenance is the fixture rated for?
- What happens to my heating load, and is it in the payback calculation?
Frequently Asked Questions
Can I Replace My HPS Fixtures With LED One for One?
In most cases yes. Our 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. We still model the existing layout and return fixture count, spacing, and connected load before a quote, since mounting height and DLI target decide the final spec.
How Long Is the Payback Period on an LED Retrofit?
It depends on your energy rate, your rebate eligibility, your crop, and your heating situation, which is why a general figure is not useful. A payback calculation is only meaningful when it is built on your facility’s actual numbers.
Will My Yields Change If I Switch to LED?
Total daily light delivered to the canopy, the DLI, is the main driver of yield, and a properly planned LED layout is designed to hit the same target DLI and uniformity. Expect to re-tune the environment rather than the light plan, because leaf temperature runs lower under LED at the same intensity, so temperature setpoints and irrigation usually need adjusting. Set up a trial area before a full conversion so you can see how your specific crop responds.
Do LEDs Need Maintenance?
Yes. Dust and film on the lens cost output the same way a dirty reflector does, so lens cleaning belongs on the regular maintenance schedule, and drivers are worth building into the service plan as the most common failure point on any LED luminaire. Turn off and lock out the branch circuit and let the luminaires cool completely before starting, then follow our guide to cleaning horticultural luminaires for the correct procedure. Never use commercial cleaning products, soaps, or detergents on the lens.
Should I Go Fully LED or Hybrid?
Hybrid is often the better answer for greenhouses in cold climates that rely on radiant heat through winter, and for operations wanting to limit upfront capital. Full LED tends to suit indoor facilities where cooling load is the constraint.
Getting a Number You Can Budget Against
Every retrofit number that matters is specific to your building, your crop, and your energy rate. Our ROI Guide for LED versus HPS walks through the same calculation if you want to sketch the numbers yourself first. The P.L. Light Systems team will model your existing layout and return fixture count, spacing, and connected load, and your sales manager can point you at the rebate programs worth checking in your region.
Tell us your crop, structure, and targets. We engineer the rest.
