LIGHTING TECHNOLOGY COMPARISON
Compare LED and high-pressure sodium lighting for commercial cultivation, including efficacy, heat management, light distribution, control, maintenance and long-term operating considerations.
COMPARISON FOUNDATION
High-pressure sodium lighting has supported commercial greenhouse production for decades. Modern LED grow lights use a different approach, offering greater flexibility in fixture design, light distribution, spectrum and control.
The objective, however, remains the same: deliver the required light to the complete crop area while supporting production quality, facility climate and economically sustainable operation.
A meaningful comparison should therefore consider the complete growing system—not fixture wattage or purchase price alone.
Can the proposed system deliver the target PPFD, DLI and uniformity across the complete cultivated area?
How much input power is required to produce and distribute the necessary photosynthetic photon output?
How will radiant heat, convective heat and installed lighting power affect crop temperature and environmental control?
What are the installation, energy, maintenance, infrastructure and operational implications over the system’s useful life?
AT A GLANCE
The characteristics below describe common differences between modern horticultural LED systems and traditional HPS installations. Actual performance varies by fixture, lamp, reflector, driver or ballast, installation geometry and operating conditions.
| Consideration | LED Grow Lights | HPS Lighting |
|---|---|---|
| Photon efficacy | Modern systems generally produce more photosynthetic photons per joule of electrical input. | Traditional systems generally require more electrical input for an equivalent photon output. |
| Heat directed toward the crop | Typically directs less infrared radiation toward the canopy. Most fixture heat is transferred to the surrounding air and structure. | Produces more infrared radiation that can raise leaf and surface temperatures. |
| Light distribution | Different fixture forms and optics can provide broad or targeted light distributions. | Distribution depends strongly on lamp position, reflector geometry, cleanliness and mounting height. |
| Spectrum | Can provide broad-white, red-dominant or application-specific spectral combinations. | Provides a largely fixed spectrum with strong yellow, orange and red output. |
| Dimming and control | Commonly supports responsive dimming and integration with compatible lighting controls. | Control and dimming capabilities are more limited and depend on the lamp-and-ballast system. |
| Maintenance | Does not require scheduled lamp replacement, although drivers and other components may eventually need service. | Lamps and reflectors require inspection, cleaning and periodic replacement as performance changes. |
| Initial investment | Often requires a higher initial fixture investment. | Existing equipment may reduce short-term capital requirements. |
| Retrofit implications | May change electrical load, radiant heat, mounting arrangements and environmental setpoints. | Existing infrastructure may already be matched to the present lamps, reflectors and thermal contribution. |
Independent technical references: U.S. Department of Energy and DesignLights Consortium.
This is a general technology comparison, not a product-performance guarantee. Evaluate specific lighting systems using verified electrical, photometric and horticultural data under the intended project conditions.
ENERGY CONVERSION
Horticultural lighting efficacy describes how effectively a fixture converts electrical input into photosynthetic photon output. It is expressed in micromoles per joule (µmol/J).
A fixture with higher efficacy can produce the same PPF using less electrical power, or produce more photons from the same input power. Modern horticultural LED fixtures generally achieve higher efficacy than traditional HPS systems.
Efficacy is important, but it does not show how effectively the emitted light reaches the crop. Fixture output must also be considered alongside light distribution, mounting height, spacing, structural obstructions and canopy-level uniformity.
This calculation compares the fixture’s total photosynthetic photon output with the electrical power it consumes. Use verified fixture data measured under clearly identified operating conditions.
Fixture wattage alone does not determine which lighting system uses less energy. A meaningful comparison should evaluate the electrical power required to achieve the same target average PPFD, minimum PPFD and uniformity across the same cultivated area.
Include the complete fixture quantity, actual input power, dimming schedule and annual operating hours. An LED retrofit does not necessarily require the same fixture count, wattage or mounting arrangement as the existing HPS installation.
Higher fixture efficacy creates an opportunity for energy savings, but the final result depends on the complete lighting layout and operating strategy.
FACILITY CLIMATE
Both LED and HPS lighting systems introduce heat into the growing environment. An important difference is how that energy reaches the crop and surrounding facility.
LED grow lights
LED fixtures typically direct less infrared radiation toward the canopy. Much of their heat is transferred through the fixture body and into the surrounding air. When LEDs require less input power to deliver an equivalent lighting result, the total heat introduced by the lighting system may also decrease.
HPS lighting
HPS lamps emit more infrared radiation toward the crop. This radiant energy can increase leaf, canopy and surface temperatures even when the measured air temperature remains unchanged.
Changing from HPS to LED can therefore alter the relationship between air temperature and crop temperature. Heating, ventilation, irrigation, humidity management and environmental setpoints may need to be reviewed following a retrofit.
LED fixtures still release heat into the growing facility. They may reduce radiant heat at crop level and lower the total lighting heat load when less electrical power is required, but the remaining heat must still be managed.
Evaluate lighting heat together with the facility’s heating, cooling, ventilation and dehumidification systems. The operational effect will differ between a greenhouse influenced by outdoor conditions and a fully enclosed growing environment.
During cold periods, heat from HPS lighting may offset part of a greenhouse’s heating demand. Replacing it with a lower power LED system can reduce this contribution and may require additional heat from the greenhouse heating system.
During warmer or sunnier periods, lower lighting power and reduced radiant heat may allow supplemental lighting to operate longer without exceeding crop-temperature or climate limits.
In a fully enclosed facility, nearly all electrical energy consumed by the lighting system ultimately becomes heat within the controlled environment.
A more efficacious lighting design can reduce the electrical load and associated cooling demand while maintaining the required crop-level light—but the remaining fixture and equipment heat must still be removed.
CANOPY COVERAGE
Lighting performance depends not only on how many photons a fixture produces, but also on how effectively those photons are distributed across the cultivated area.
LED fixtures are available in several formats—including multi-bar, linear and compact top-light designs—with different optics and beam patterns. This flexibility can help a lighting layout match crop geometry, greenhouse structure, mounting height and target uniformity.
HPS systems generally use a compact lamp combined with a reflector. Their distribution is strongly affected by reflector design, lamp position, mounting height, cleanliness and overlap between neighbouring fixtures.
Neither technology provides good uniformity automatically. The complete layout must be evaluated at crop canopy level.
Average PPFD describes the mean light intensity across the measurement area, but it does not reveal darker zones or excessive peaks.
Minimum PPFD identifies the lowest measured light level and helps reveal areas that may limit crop consistency.
Uniformity shows how evenly light is distributed. Evaluate it using a consistent measurement grid and clearly defined calculation method.
A meaningful LED-versus-HPS comparison should model or measure both systems across the same cultivated area, at the same crop height and under equivalent operating conditions.
Compare average PPFD, minimum PPFD, uniformity, edge losses and any light intercepted by structural elements. Fixture-level PPF or a single centre-point PPFD reading cannot describe the performance of the complete installation.
Mounting height also matters. Increasing the distance between the fixture and canopy can improve distribution and overlap, but it may reduce crop-level intensity and increase light reaching areas outside the intended cultivation zone.
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LIGHTING RESPONSE
LED and HPS systems differ significantly in their ability to tailor light output and respond to changing production conditions.
HPS lamps provide a largely fixed spectrum determined by the lamp technology. Traditional systems are commonly operated at full output, although compatible ballasts may offer stepped or limited dimming.
LED systems can be designed with different spectral combinations and generally provide more responsive dimming. When integrated with compatible controls and sensors, output can be adjusted according to daylight availability, crop stage, lighting schedule or facility-management strategy.
These capabilities create operational flexibility, but only when the fixture, driver, control protocol and environmental-control system are properly matched.
LED fixtures can use broad-white, red dominant or application-specific spectra. HPS delivers a comparatively fixed spectrum with strong yellow, orange and red output.
Compatible LED systems can generally dim smoothly over a broad operating range. HPS dimming is more limited and may affect lamp performance, spectrum or system efficiency.
LED output can be coordinated with schedules, daylight sensors and greenhouse-control strategies. Available functions depend on the selected driver, protocol and control architecture.
Responsive dimming can help maintain a supplemental-light target as natural sunlight changes throughout the day. It may also reduce unnecessary electricity use, limit demand peaks and support more consistent lighting conditions.
The most appropriate control strategy may use an instantaneous PPFD target, a cumulative DLI target, a time schedule or a combination of these approaches. Sensor position, calibration, response time and system commissioning are essential to reliable operation.
Spectral selection and control strategies should be based on the crop, production objectives and complete growing environment—not on light colour alone.
LONG-TERM OPERATION
Lighting-system value extends beyond initial efficacy and purchase price. Maintenance requirements, component accessibility, electrical compatibility and the condition of existing infrastructure can materially affect long-term performance and project cost.
LED fixtures eliminate scheduled lamp replacement, but they are not maintenance-free. Drivers, connectors, seals, lenses, heat-dissipation surfaces and control components should remain accessible for inspection and service.
HPS installations require lamp and reflector maintenance. Output can change as lamps age, while dust, mineral deposits and reflector degradation can reduce the amount of light reaching the crop.
Review rated lifetime data, warranty terms, driver accessibility, connector quality, ingress protection and the availability of replacement components.
Cleaning requirements remain important, particularly in humid, dusty or chemically demanding growing environments. Maintenance procedures must follow the manufacturer’s instructions.
Include scheduled lamp replacement, reflector cleaning or replacement, ballast condition and the labour required to service fixtures above the crop.
When evaluating an existing system, document lamp age and maintenance history. A poorly maintained HPS installation should not be treated as representative of a properly maintained new system.
An established HPS installation may already have compatible branch circuits, mounting points, control equipment and spare components. Reusing suitable infrastructure can reduce initial project cost.
An LED retrofit may require changes to circuit loading, connectors, mounting hardware, fixture spacing, controls or environmental settings. At the same time, reduced connected load may release electrical capacity for expansion or other equipment.
Before selecting a retrofit approach, verify voltage, circuit capacity, conductor sizing, overcurrent protection, connector compatibility, control wiring and structural support with qualified professionals.
Electrical installation and modification must comply with applicable codes, product certifications and local authority requirements.
PROJECT PATH
The best lighting solution depends partly on whether the project is replacing an existing HPS installation or designing a new growing facility.
A retrofit begins with established structural, electrical and environmental conditions. A new project provides greater design flexibility, but lighting decisions must be coordinated early with the building, greenhouse and cultivation systems.
In both cases, compare complete project outcomes rather than assuming that one LED fixture should directly replace one HPS fixture.
Begin by documenting the existing fixture count, actual input power, voltage, circuit arrangement, mounting height, spacing, controls and annual operating schedule.
Measure crop-level PPFD and uniformity where practical, and record lamp age, maintenance condition and climate-management practices. This establishes a reliable baseline for comparing proposed LED layouts.
Also evaluate how reduced electrical demand and radiant heat may affect heating, cooling, humidity, irrigation and crop temperature.
Define the crop, cultivated area, target PPFD, photoperiod, DLI objective and expected contribution from natural daylight before selecting fixtures.
Coordinate the lighting design with structural supports, electrical distribution, environmental controls, irrigation and future service access. Early coordination can prevent avoidable compromises in fixture spacing, uniformity and system control.
Consider future production changes or facility expansion when planning electrical capacity and control zones.
A one-for-one fixture replacement may be convenient, but it should not be assumed. LED and HPS fixtures can differ in photon output, distribution, mounting requirements and optimal spacing.
The correct fixture quantity should be determined from the target crop-level result across the complete cultivated area. Depending on the proposed system, the final design may use fewer, more or the same number of fixtures as the existing installation.
Preserve what remains technically suitable, but allow the proposed lighting layout to be designed around the crop’s requirements rather than the previous fixture positions.
ESTIMATE OPERATING IMPACT
Fixture efficacy and layout performance are only part of the decision. Annual operating hours, system wattage and electricity rates determine how lighting choices affect energy consumption and operating costs.
Use the LED vs HPS Energy Savings Calculator to compare two complete lighting systems and estimate annual electricity use, energy costs, potential savings and simple payback.
The results are preliminary planning estimates. Confirm final project economics using verified fixture data, the proposed lighting layout, applicable utility rates and actual installation costs.
No contact information is required to use the calculator.
PROJECT EVALUATION
Use these five steps to compare complete lighting systems based on crop requirements, facility conditions and long term operating value—not fixture specifications alone.
Document the current HPS fixture quantity, actual input power, mounting height, spacing, lamp age, maintenance history, operating schedule and control method.
Where practical, measure average PPFD, minimum PPFD and uniformity at crop canopy level. Also record electricity use, climate-management practices and seasonal operating limitations.
Identify the cultivated area, crop type, production stage, target PPFD, photoperiod and DLI objective.
For greenhouse projects, estimate the natural-light contribution by season and determine when supplemental lighting is needed to close the gap.
Evaluate the proposed LED and HPS systems across the same cultivated area and crop height.
Compare fixture quantity, actual input power, average and minimum PPFD, uniformity, mounting requirements, structural interference and controllability. Do not base the decision on a single fixture or centre-point reading.
Consider how each system affects electrical capacity, radiant heat, air temperature, crop temperature, heating, cooling, humidity, irrigation and environmental controls.
Include installation changes, maintenance labour, component replacement, product certifications and compatibility with existing infrastructure.
Calculate annual energy consumption and operating cost using realistic schedules and utility rates. Include initial equipment, installation, maintenance and expected replacement expenses.
Test more than one scenario because electricity rates, operating hours, daylight availability and crop strategy can change the result.
The preferred solution is not automatically the fixture with the highest efficacy, the lowest wattage or the lowest purchase price.
Choose the system that can reliably achieve the crop-light target while fitting the facility’s electrical, structural, environmental and operational requirements over the intended project life.
KEY TAKEAWAY
LED technology can offer higher photon efficacy, responsive dimming, flexible light distribution and reduced radiant heat at crop level. These advantages can lower electricity consumption and create greater control over the lighting strategy.
HPS may still offer practical value where suitable equipment and infrastructure already exist, where its thermal contribution supports winter greenhouse production or where short term capital limitations influence the project.
The correct decision cannot be made from fixture wattage, efficacy or purchase price alone. Compare the complete systems based on crop-level light, annual operation, facility climate, installation requirements, maintenance and long-term project value.
The best lighting system is the one that reliably meets the crop’s requirements while supporting the facility’s complete operational and economic objectives.
FREQUENTLY ASKED QUESTIONS
Modern horticultural LED fixtures generally achieve higher photon efficacy than traditional HPS systems. However, project-level energy savings depend on the complete fixture quantity, input power, layout, target PPFD, uniformity, dimming strategy and annual operating hours.
Compare both systems based on equivalent crop-level lighting results rather than fixture wattage alone.
Not necessarily. LED and HPS fixtures can differ in photon output, light distribution, mounting requirements and optimal spacing.
A one-for-one replacement may be suitable in some projects, but the correct fixture quantity should be determined through a lighting layout based on the cultivated area and target crop-level performance.
Yes. LED fixtures convert part of their electrical input into heat, which is transferred mainly through the fixture body and surrounding air.
Compared with HPS, LEDs typically direct less infrared radiation toward the crop. If the LED system also uses less electrical power, it may introduce less total heat into the facility.
It can. Heat from HPS lighting may contribute to greenhouse heating during cold periods. A lower-power LED system with less radiant heat can reduce that contribution, potentially increasing heating demand.
During warmer or sunnier conditions, reduced lighting heat may allow longer supplemental-lighting operation without exceeding crop-temperature or climate limits.
LED lighting can provide greater control over spectrum, intensity, distribution and scheduling, but technology alone does not guarantee improved production.
Results depend on the crop, cultivar, lighting target, uniformity, climate, irrigation, nutrition and overall cultivation strategy.
Compare the total input power of each proposed lighting layout, fixture quantity, operating schedule and applicable electricity rates.
Include installation, maintenance, replacement components and any changes to heating or cooling demand. Use realistic project data rather than nominal fixture wattage alone.
Suitable mounting, electrical or control infrastructure may sometimes be reused, reducing initial project cost. Compatibility must be verified for voltage, circuit loading, connectors, controls, structural support and applicable certifications.
The proposed LED layout should still be designed around the crop’s requirements rather than automatically following the previous fixture positions.
Prepare the cultivated dimensions, crop type, target PPFD or DLI, existing fixture model and quantity, actual input power, mounting height, spacing, voltage, operating schedule and electricity rate.
Existing PPFD measurements, lamp age, maintenance history, greenhouse drawings and environmental information can make the comparison more reliable.
TECHNICAL REFERENCES
The following independent resources provide additional guidance on horticultural-lighting terminology, measurement, system design and LED performance. Standards may require purchase or authorized access.
Overview of LED efficacy, spectral flexibility, radiant heat and lighting controls.
Performance, testing, reporting, safety certification and controllability requirements for qualifying horticultural LED products.
Standardized horticultural-lighting quantities and terminology.
Recommended measurement and testing methods for horticultural radiation sources, including LED and HPS equipment.
Criteria and methodologies for comparing horticultural lighting system designs and energy performance.
External resources are provided for general technical reference. CultiLight does not control third-party content or access requirements.
PROJECT SUPPORT
Every growing facility has different crop requirements, structural conditions, electrical infrastructure and environmental constraints.
CultiLight can help evaluate your cultivated area, target PPFD and DLI, existing lighting system, operating schedule and project objectives to develop an appropriate commercial lighting approach.
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