8 Greenhouse Supplemental Lighting Kits for Year-Round Growing

Winter days can turn a productive greenhouse into a cold, dark holding pen where seedlings stall and warm-season crops wither. Supplemental lighting bridges the gap between weak seasonal sun and the intense rays your plants need to thrive year-round. Choosing the right light kit transforms your backyard greenhouse from a seasonal hobby into a continuous, high-yielding food source.

Disclosure: As an Amazon Associate, this site earns from qualifying purchases. Thank you!

Understanding Greenhouse Light Requirements

Sunlight seems abundant, but greenhouse glazing materials like polycarbonate or double-strength glass can block up to 30 percent of usable light. During late autumn and winter, the angle of the sun lowers, shortening day length and leaving crops starved for energy. Supplemental lighting is not about replacing the sun entirely; it is about filling the seasonal deficit to keep plants in an active state of growth.

Plants utilize specific wavelengths of light for different growth stages, primarily blue light for vegetative leaf growth and red light for flowering and fruiting. While natural sunlight provides a full spectrum, winter light lacks the intensity required to trigger robust development. Adding targeted supplemental light ensures that winter spinach stays crisp and early tomato starts do not stretch and become leggy.

Calculating Daily Light Integral for Crops

Daily Light Integral (DLI) measures the total amount of light a plant receives over a 24-hour period, functioning like a rain gauge for light. Different crops have strict DLI minimums to produce high-quality yields. For instance, leafy greens can get by on a DLI of 10 to 14, while fruiting crops like tomatoes or peppers demand a minimum DLI of 20 to 30 to set fruit successfully.

To calculate your greenhouse DLI, you need to combine the natural light passing through your glazing with the output of your supplemental fixtures. You can estimate this using a PAR meter to measure Photosynthetic Active Radiation (PAR) at canopy level, then multiplying that intensity by the number of hours your lights run daily. Over-lighting wastes expensive electricity, while under-lighting leads to disappointing, slow-growing crops.

LED Grow Light Bar – Spider Farmer SF600

Low-profile light bars are the backbone of propagation benches and multi-tier shelving units in a small greenhouse. They deliver gentle, even light across narrow spaces without generating excessive heat that can dry out delicate seed-starting plugs. The Spider Farmer SF600 excels in this role, utilizing efficient OSRAM diodes to provide a full-spectrum light that mimics natural spring sunshine.

This fixture draws very little power while delivering a surprising amount of light, making it incredibly cheap to run during long winter nights. The slim, lightweight design allows it to hang from delicate greenhouse framing or fit beneath tight shelving.

• Power Draw: 74 Watts
• Coverage: 2′ x 4′ for vegetative growth
• Spectrum: 660nm (Red), 3000K, 5000K, and IR

Because this light uses passive cooling without loud fans, it operates silently and has fewer moving parts to fail in a humid greenhouse environment. However, its light penetration is shallow, meaning it must be kept close to the canopy and is not suitable for tall, mature fruiting plants. This kit is perfect for backyard growers focusing on winter salad greens, microgreens, and spring seedling starts, but it will not satisfy mature tomatoes.

High-Output LED – Horticultural Lighting Group 650R

When growing heavy-feeding, tall crops like winter tomatoes or cucumbers, standard shop lights simply cannot penetrate the dense leaf canopy. High-output LEDs act as a sun replacement, throwing deep-penetrating light down to the lower branches where fruit sets. The Horticultural Lighting Group 650R is designed specifically to maximize canopy penetration with its custom-designed Quantum Boards.

This fixture delivers massive light output while pulling power from the wall, featuring top-bin Samsung and deep-red Osram diodes. The heavy-duty aluminum heatsink keeps the unit running cool without fans, protecting the electronics from the dusty, damp air of a working greenhouse.

• Power Draw: 630 Watts
• Coverage: 5′ x 5′ for vegetative, 4′ x 4′ for flowering
• Dimming Range: 60 to 630 Watts

Keep in mind that this is a heavy, powerful light that requires sturdy overhead trusses to hang safely. The intense light output can easily bleach young seedlings if hung too close, so utilizing the built-in manual dimmer is essential during early growth stages. It is an investment-grade light best suited for serious year-round food producers, and is far too powerful for simple seed starting or shallow shelving.

T5 Fluorescent Fixture – Hydrofarm Agrobrite T5

Fluorescent fixtures have been the reliable workhorse of backyard growers for decades due to their dependable, diffused light and low upfront cost. They are ideal for germinating seeds and maintaining mother plants because they spread light evenly over a wide rectangular footprint. The Hydrofarm Agrobrite T5 features a highly reflective aluminum interior that directs every bit of light down toward your flats.

This fixture runs cool enough to sit just inches above your plant canopies without the risk of burning leaves, which helps prevent seedlings from stretching. It houses multiple high-output tubes that can be switched on or off independently to customize light levels as your plants grow.

• Tube Count: 4 tubes (4-foot length)
• Output: 20,000 Lumens
• Color Temperature: 6400K (ideal for vegetative growth)

While highly reliable, fluorescent tubes are less energy-efficient than modern LEDs and require replacement every few seasons as their light output degrades. The fixture itself is also bulky, taking up valuable overhead space in small hoop houses. This classic setup is perfect for budget-conscious growers who need a dependable, easy-to-use system for spring seed starting and vegetative propagation.

CMH Grow Light – Sun System LEC 315 RA Kit

Ceramic Metal Halide (CMH) lights provide a rich, full spectrum that closely mimics natural sunlight, including beneficial UV and infrared wavelengths. This natural light spectrum improves overall plant health, strengthens stems, and enhances the flavor of herbs and vegetables. The Sun System LEC 315 RA Kit utilizes a highly reflective integrated reflector to maximize this high-quality light distribution.

The ceramic arc tube in this fixture allows the lamp to burn at higher temperatures than traditional metal halides, producing more light per watt. This kit runs on a highly efficient ballast integrated directly into the fixture, reducing messy cord clutter in your greenhouse.

• Power Draw: 315 Watts
• Lamp Type: Ceramic Metal Halide (LEC)
• Reflector: Highly reflective textured aluminum

Because CMH bulbs emit a significant amount of heat, they can help warm a cold winter greenhouse, but they require careful placement to avoid overheating plants in late spring. The bulbs also have a strict orientation requirement and must be handled with care to avoid getting skin oils on the glass. This kit is ideal for growers seeking maximum crop quality and natural plant development, but it is not suitable for tight spaces with low vertical clearance.

DE HPS Grow Light – Gavita Pro 1000e DE

Double-ended High-Pressure Sodium (DE HPS) lights are the traditional choice for professional greenhouse supplemental lighting due to their unmatched raw light output and deep canopy penetration. The double-ended design secures the bulb at both ends, ensuring a more stable arc and longer lamp life than single-ended bulbs. The Gavita Pro 1000e DE is a legendary fixture that delivers consistent, high-intensity light designed to keep fruiting crops productive through the darkest winter months.

This fixture operates at high frequencies, which increases the efficiency of the bulb and delivers a spectrum rich in red and orange wavelengths perfect for heavy fruiting. The integrated electronic ballast can be controlled remotely, allowing you to dim or boost the light output based on weather conditions.

• Power Draw: 1000 Watts
• Output Control: Adjustable from 500W to 1150W
• Connection: 240V compatible for efficient power draw

The primary drawback for hobbyists is the intense heat generated by HPS bulbs, which requires a tall greenhouse ceiling—at least 8 to 10 feet of clearance—to prevent leaf scorch. They also pull a massive amount of electricity, which can strain standard home electrical panels. This commercial-grade fixture is best for dedicated growers with large, high-ceiling greenhouses who prioritize raw winter yields over energy savings.

Waterproof LED Strip – Barina T8 Grow Light

Greenhouses are inherently wet environments, filled with overspray, condensation, and dripping water from overhead structures. Standard indoor grow lights can quickly short out or rust under these harsh conditions, posing safety hazards. Waterproof LED strips solve this issue by sealing the electronics against moisture while providing flexible, modular light placement. The Barina T8 Grow Light multi-pack offers wet-rated, linkable fixtures that bring light directly to your lower shelves and humid propagation zones.

These lightweight strips can be daisy-chained together, allowing you to run multiple lights from a single wall outlet and reducing cable clutter. They emit very little heat, allowing you to mount them directly to the underside of wire benches or wooden shelves.

• Wattage: 24 Watts per strip
• Linkability: Up to 6 lights in a single run
• Spectrum: Yellow full spectrum for all growth stages

While incredibly convenient and safe for wet zones, these low-wattage strips lack the power to grow tall, light-hungry crops to maturity. They are designed for leafy greens, herbs, and starting seeds on multi-tier racks. This budget-friendly kit is the perfect match for backyard hobbyists who need a safe, water-resistant solution for tight propagation spaces.

Commercial LED Fixture – Fluence SPYDR 2x

For serious growers looking to maximize every square inch of a large greenhouse bench, uniform light distribution is critical. Standard single-point lights create hot spots directly underneath the bulb and dark corners at the edges of the bench. The Fluence SPYDR 2x utilizes a multi-bar design that spreads light evenly across a wide footprint, ensuring that plants at the edge grow just as fast as those in the center.

Engineered for close-proximity cultivation, this fixture can hang as close as 6 inches from the plant canopy without causing light burn. The industrial-grade build features an IP66 wet rating, meaning it can withstand heavy greenhouse humidity and direct water spray during cleaning.

• Power Draw: 345 Watts
• Coverage: 4′ x 4′ footprint
• PPF (Light Output): 860 µmol/s

The primary consideration for this fixture is its high initial cost, which represents a significant investment for a part-time grower. Additionally, its wide physical footprint means it can block some natural sunlight during the day if mounted too low in a small greenhouse. It is the ultimate choice for serious hobbyists or small-scale market gardeners who demand professional-grade reliability and perfectly uniform crop growth.

Compact LED Board – Mars Hydro TS 1000

Not every greenhouse grower needs to light an entire building; often, you just need to keep a small 3×3 foot corner productive through the winter. Compact LED boards provide a highly efficient, budget-friendly way to deliver intense light to a localized area. The Mars Hydro TS 1000 is a classic entry-level quantum board that offers impressive light output without a premium price tag.

This fixture uses a highly reflective aluminum hood design that bounces stray light back down to the plants, maximizing its 150-watt power draw. It features a fanless design for silent operation, relying on a lightweight aluminum plate to dissipate heat away from the LEDs.

• Power Draw: 150 Watts
• Coverage: 3′ x 3′ for vegetative, 2.5′ x 2.5′ for flowering
• Dimming: Daisy-chain dimming capability

Because the driver (the power supply) is mounted on top of the light, it can run warm, but Mars Hydro’s design allows you to remove the driver and mount it outside your growing area via an extension cord. The light spectrum is heavily weighted toward white and red, which is excellent for general plant growth but may require adjustment for specific blue-loving seedlings. This light is an exceptional choice for the hobbyist looking to keep a small collection of winter vegetables or container citrus thriving.

How to Safely Hang Lights in Your Greenhouse

Hanging heavy electrical equipment inside a damp, wind-exposed greenhouse requires careful planning and robust hardware. Never rely on cheap plastic zip ties or thin wire that can degrade under UV exposure and snap, dropping expensive fixtures onto your plants. Use heavy-duty steel chains, rated carabiners, or adjustable rope ratchets that allow you to easily raise and lower the lights as your plants grow.

Ensure your greenhouse frame can handle the weight of the fixtures, especially if you live in an area prone to heavy snow loads that already stress the structure. Attach your hanging hardware directly to the structural metal bows or wooden purlins, rather than the thin glazing tracks. Always route electrical cords along the frame using UV-resistant clips, keeping them well away from standing water and walkways where they could become tripping hazards.

Managing Heat and Humidity Around Grow Lights

Grow lights inevitably alter the microclimate of your greenhouse by introducing heat and electrical currents to a high-humidity environment. High humidity can cause condensation to form inside non-waterproof fixtures, leading to short circuits or premature bulb failure. Operating oscillating fans near your lights helps disperse pockets of humid air, preventing moisture from settling on warm electrical components.

While the heat generated by HID lights can help warm a cold winter greenhouse, it can quickly become a liability during sunny spring days. Use automated ventilation systems, such as louvers or exhaust fans connected to a thermostat, to dump excess heat before it stresses your crops. Monitoring your greenhouse with a reliable hygrometer ensures you keep humidity below 70 percent, protecting both your plant health and your lighting investment.

Introducing supplemental lighting to your greenhouse removes the seasonal limits of backyard farming, allowing you to harvest fresh produce even in the dead of winter. By matching the right fixture to your specific crop needs and greenhouse structure, you create a resilient, year-round growing system. Hang your lights securely, monitor your climate, and enjoy the satisfaction of a thriving, productive greenhouse all year long.