LED Grow Light ROI for Leafy Greens: Spectrum, Wattage, and Payback

Lighting is the single largest operating expense in most vertical farms — typically 25-35% of total operating costs, according to Cornell University's Controlled Environment Agriculture program. Get the lighting wrong and you're either burning money on energy for light the plants can't use, or under-lighting your crops and leaving yield on the table. Get it right and you have a competitive advantage that compounds with every harvest cycle.

As we detail in our comprehensive guide to vertical farming and controlled environment agriculture, the economics of vertical farming are tight enough that optimizing every input matters. Lighting optimization — choosing the right spectrum, the right wattage, and the right fixture for your specific crops — is one of the highest-leverage decisions you'll make in designing or upgrading a vertical farm. Here's what the science and the economics actually say.

Understanding Light Metrics: What Actually Drives Plant Growth

Before evaluating specific fixtures, you need to understand the metrics that matter for plant growth — because the marketing numbers on grow light spec sheets are often designed to impress rather than inform.

PAR (Photosynthetically Active Radiation): The range of light wavelengths (400-700nm) that plants use for photosynthesis. PAR is the relevant metric for plant growth — light outside this range (UV below 400nm, far-red and infrared above 700nm) has secondary effects but doesn't drive primary photosynthesis.

PPF (Photosynthetic Photon Flux): The total amount of PAR light a fixture emits per second, measured in micromoles per second (µmol/s). This is the fixture's total light output — useful for comparing fixtures but doesn't tell you how much light reaches the plant canopy.

PPFD (Photosynthetic Photon Flux Density): The amount of PAR light that reaches a specific surface area, measured in µmol/m²/s. This is the most important metric for growing — it tells you how much light your plants are actually receiving. PPFD varies significantly with distance from the fixture and fixture design.

DLI (Daily Light Integral): The total amount of PAR light delivered to the plant canopy over a full day, measured in mol/m²/day. DLI = PPFD × photoperiod (hours) × 0.0036. This is the most useful metric for crop planning because it integrates both light intensity and duration. Leafy greens typically require a DLI of 12-17 mol/m²/day for commercial production.

Efficacy (µmol/J): How efficiently the fixture converts electrical energy into PAR light. Higher efficacy means more light per watt of electricity consumed. Modern commercial LED fixtures achieve 2.5-3.5 µmol/J; HPS fixtures typically achieve 1.5-1.8 µmol/J. This is the key metric for energy cost comparison.

Spectrum Science: What Wavelengths Leafy Greens Actually Need

The spectrum debate in vertical farming has evolved significantly as more research has accumulated. The early assumption that plants only need red and blue light (the "blurple" era) has been replaced by a more nuanced understanding.

Red light (630-660nm) is the primary driver of photosynthesis and biomass accumulation in leafy greens. Chlorophyll a and b absorb red light most efficiently, and red-driven photosynthesis produces the carbohydrates that become leaf mass. High red ratios produce fast-growing, high-yield plants — but plants grown under red-only light tend to stretch (etiolate) and have poor structural integrity.

Blue light (430-450nm) regulates plant morphology through phototropins and cryptochromes. Blue light suppresses stem elongation (keeping plants compact and structurally sound), regulates stomatal opening (affecting water use and gas exchange), and influences the production of flavor compounds and pigments. Basil grown under higher blue ratios has measurably higher essential oil content and more intense flavor.

Green light (500-560nm) was long dismissed as irrelevant because chlorophyll absorbs it less efficiently than red or blue. More recent research from Cornell and other institutions has shown that green light penetrates deeper into the leaf canopy than red or blue, driving photosynthesis in lower leaf layers. Full-spectrum white LEDs that include green light consistently outperform narrow-band red/blue fixtures in canopy-level yield studies.

Far-red light (700-750nm) activates the Emerson Enhancement Effect — when combined with red light, far-red light increases the efficiency of photosynthesis beyond what either wavelength achieves alone. Adding far-red to a red/blue spectrum can increase photosynthetic efficiency by 10-20% and accelerate crop cycle time. Several commercial fixtures now include far-red channels specifically for this purpose.

Practical spectrum recommendation for leafy greens: A broad-spectrum white LED with a color temperature of 3000-4000K, supplemented with additional red (660nm) and blue (450nm) channels, gives you the flexibility to tune spectrum for different crops while providing the green light penetration that narrow-band fixtures miss. A red-to-blue ratio of 4:1 to 6:1 is the starting point for most leafy greens, with adjustment based on crop response.

Top LED Fixtures for Commercial Leafy Green Production

Fluence SPYDR 2p: Industry Standard for Vertical Farms

Fluence (a Signify/Philips company) has become the dominant LED fixture supplier for commercial vertical farming operations globally. The SPYDR 2p is their flagship vertical farming fixture, designed specifically for multi-tier rack systems with tight vertical spacing.

Specs: 645W input power, 1,870 µmol/s PPF, 2.9 µmol/J efficacy. Designed for 6-12 inch mounting height above canopy. Available in multiple spectrum configurations including PhysioSpec Indoor (broad spectrum) and PhysioSpec Greenhouse.

Cost: Approximately $800-1,000 per fixture. For a 10,000 sq ft facility with 4-tier racks, expect 400-600 fixtures — a lighting investment of $320,000-600,000.

Performance: Fluence's published data from commercial deployments shows lettuce yields of 3.5-4.5 lbs per square foot per year at 18-hour photoperiods. Independent evaluations at Cornell's CEA program have validated these yield figures in controlled trials.

Best for: Commercial operations of 5,000+ sq ft that want the most proven, well-supported fixture in the industry. Fluence's technical support and crop science resources are the best in the category.

Gavita Pro 1700e LED: Best for Retrofit from HPS

Gavita (owned by Scotts Miracle-Gro) has built its reputation in greenhouse production and has adapted its expertise to vertical farming. The Pro 1700e is designed as a direct replacement for 1000W HPS fixtures, making it the natural choice for operations retrofitting from HPS.

Specs: 645W input power, 1,700 µmol/s PPF, 2.6 µmol/J efficacy. Compatible with Gavita's Master Controller for centralized dimming and scheduling.

Cost: Approximately $700-900 per fixture. Slightly lower efficacy than Fluence but strong integration with Gavita's controller ecosystem.

Best for: Operations transitioning from HPS who want a direct fixture replacement with minimal system redesign. The Master Controller integration makes managing large numbers of fixtures straightforward.

Heliospectra ELIXIA: Best for Spectrum Control

Heliospectra's ELIXIA fixture offers the most granular spectrum control of any commercial vertical farming LED — eight independently controllable channels covering UV, blue, green, red, far-red, and white. This flexibility allows precise spectrum tuning for different crops and growth stages.

Specs: 600W input power, 1,560 µmol/s PPF, 2.6 µmol/J efficacy. Software-controlled spectrum and intensity via Heliospectra's Heliocone platform.

Cost: Approximately $1,200-1,500 per fixture — the premium reflects the spectrum control capability. Higher upfront cost but enables research-grade spectrum optimization.

Best for: Operations growing multiple crop types with different spectrum requirements, or operations that want to conduct their own spectrum optimization research to develop a competitive advantage.

Grower's Choice ROI-E720: Best Value for Smaller Operations

For operations under 5,000 sq ft or those building their first vertical farm, Grower's Choice offers commercial-grade performance at a significantly lower price point.

Specs: 720W input power, 1,944 µmol/s PPF, 2.7 µmol/J efficacy. Full-spectrum white with red and blue supplementation.

Cost: Approximately $500-650 per fixture — 30-40% less than Fluence or Gavita at comparable efficacy.

Best for: Smaller commercial operations and new entrants who need commercial-grade performance without the premium price of the top-tier brands. The efficacy is competitive with more expensive fixtures; the difference is primarily in build quality longevity and technical support depth.

Energy Cost Analysis: The Math Behind the ROI

Lighting ROI for a vertical farm has two components: the energy cost savings versus alternative lighting technologies, and the yield revenue generated by the lighting investment.

Energy cost comparison (LED vs HPS):

A 1,000W HPS fixture produces approximately 1,700 µmol/s PPF at 1.7 µmol/J efficacy. A Fluence SPYDR 2p produces 1,870 µmol/s PPF at 645W — more light output at 35% less energy.

For a 10,000 sq ft facility with 500 fixtures running 18 hours per day, 365 days per year:

• HPS: 500 × 1,000W × 18h × 365 = 3,285,000 kWh/year
• LED (Fluence): 500 × 645W × 18h × 365 = 2,118,825 kWh/year
• Annual energy savings: 1,166,175 kWh × $0.10/kWh = $116,617/year

At a fixture cost premium of $300 per fixture over HPS (LED at $900 vs HPS at $600), the 500-fixture premium is $150,000 — recovered in 1.3 years from energy savings alone, before accounting for the longer LED lifespan (50,000+ hours vs 10,000-15,000 hours for HPS) and the elimination of HPS lamp replacement costs ($15-25 per lamp every 12-18 months).

Yield revenue analysis:

A well-managed vertical farm growing butterhead lettuce under optimized LED lighting can achieve:

• 4 lbs per square foot per year (52 harvest cycles × 0.077 lbs/sq ft per cycle at 7-day cycle time)
• 10,000 sq ft growing area × 4 lbs/sq ft = 40,000 lbs/year
• Wholesale price: $8-10/lb for premium indoor lettuce
• Annual revenue: $320,000-400,000

Lighting investment of $450,000-500,000 (500 fixtures at $900-1,000 each) represents 1.1-1.6 years of revenue — a reasonable payback for a capital asset with a 10-15 year lifespan.

Optimizing Your Lighting System: Practical Implementation

Photoperiod optimization: Most leafy greens respond well to 16-18 hour photoperiods. Extending beyond 18 hours produces diminishing returns for most species and increases energy cost without proportional yield benefit. Lettuce is a long-day plant and responds positively to 18-hour photoperiods; spinach and arugula perform well at 16 hours.

Dimming and scheduling: Modern LED fixtures support 0-100% dimming via 0-10V or PWM control. Use dimming to match light intensity to crop growth stage — seedlings and young transplants need lower PPFD (100-200 µmol/m²/s) than mature plants approaching harvest (250-350 µmol/m²/s). Dimming during off-peak electricity hours can also reduce energy costs in markets with time-of-use pricing.

Uniformity: Light uniformity across the growing surface matters as much as average PPFD. A fixture that delivers 300 µmol/m²/s at the center and 150 µmol/m²/s at the edges will produce uneven crop development and inconsistent harvest timing. Evaluate fixture uniformity maps (available from reputable manufacturers) and design fixture spacing to achieve a uniformity ratio of at least 0.7 (minimum PPFD / average PPFD).

Thermal management: LED fixtures generate heat that must be managed to maintain canopy temperature in the optimal range (65-72°F for most leafy greens). In multi-tier rack systems, heat from upper tiers affects lower tiers. Design your HVAC system to account for the heat load from lighting — typically 3,000-4,000 BTU/hour per 1,000W of lighting.

Key Takeaways

• Lighting is 25-35% of vertical farm operating costs — optimizing spectrum, wattage, and fixture selection is one of the highest-leverage decisions in vertical farm design.
• Target a DLI of 12-17 mol/m²/day for most leafy greens, achieved with 25-30 watts per square foot at 16-18 hour photoperiods.
• Modern LED fixtures achieve 2.5-3.5 µmol/J efficacy versus 1.5-1.8 µmol/J for HPS — a 40-60% energy efficiency advantage that typically pays back the LED premium in 1-2 years.
• Fluence SPYDR 2p is the industry standard for commercial vertical farms; Gavita Pro 1700e is the best retrofit option from HPS; Heliospectra ELIXIA offers the most spectrum control flexibility.
• Full-spectrum white LEDs with supplemental red and blue channels outperform narrow-band red/blue fixtures in canopy yield studies due to green light penetration into lower leaf layers.

Frequently Asked Questions

What LED spectrum is best for leafy greens in vertical farming?

Leafy greens grow well under a broad spectrum with a red-to-blue ratio of approximately 4:1 to 6:1. Red light (630-660nm) drives photosynthesis and biomass accumulation; blue light (430-450nm) regulates plant morphology and prevents stretching. Full-spectrum white LEDs with supplemental red and blue channels outperform narrow-band red/blue fixtures in canopy yield studies because green light penetrates deeper into the leaf canopy.

How many watts per square foot do leafy greens need in a vertical farm?

Leafy greens typically require 20-40 watts per square foot of growing area at a target DLI of 12-17 mol/m²/day. Running lights 16-18 hours per day at 25-30 watts per square foot typically achieves the target DLI for lettuce, spinach, and arugula. Herbs like basil require slightly higher DLI (14-20 mol/m²/day) and benefit from the higher end of the wattage range.

What is the payback period for LED grow lights in a vertical farm?

For operations retrofitting from HPS, the LED premium typically pays back in 1-2 years from energy savings alone. For new builds, lighting payback is calculated against revenue generated — typically 1.1-1.6 years of revenue for a well-managed 10,000 sq ft leafy green facility at $8-10/lb wholesale pricing. LED fixtures also have 3-5x longer lifespan than HPS, reducing replacement costs over the facility's operating life.

Which LED grow light brands are best for commercial vertical farming?

The leading commercial LED grow light manufacturers for vertical farming in 2026 are Fluence (SPYDR 2p — industry standard), Gavita (Pro 1700e — best HPS retrofit), Heliospectra (ELIXIA — best spectrum control), and Grower's Choice (ROI-E720 — best value for smaller operations). Fluence is the most widely deployed in commercial leafy green operations globally.

How does LED lighting compare to HPS for vertical farming energy costs?

Modern LED grow lights are 40-60% more energy efficient than HPS at equivalent light output. A 645W LED fixture producing 1,870 µmol/s replaces a 1,000W HPS producing 1,700 µmol/s. For a 10,000 sq ft facility with 500 fixtures running 18 hours per day, switching from HPS to LED saves approximately $116,000 per year in electricity at $0.10/kWh — recovering the fixture cost premium in 1-2 years.