For most of the year, plants in your greenhouse do just fine with natural light. However, in order for your plants to flourish year-round, you might need to supplement with grow lights. For example, maybe light gets blocked by trees, shelving units, or even other plants; or the days are simply getting too short to provide your plants with sufficient bright light.
Whether you’re just starting out or are an experienced greenhouse gardener, grow lights are a great addition to any greenhouse. These artificial lighting systems can supplement or even completely replace natural sunlight, as long as you pick the right ones for your gardening needs. Factors such as illumination, cost, and light spectrum are all important considerations when it comes to choosing grow lights for your greenhouse.
If you’re struggling with inadequate lighting in your greenhouse, grow lights are the solution for you. The right amount of supplemental light not only enhances photosynthesis, but speeds up germination and guarantees healthy blooms. Keep reading to learn everything you need to know to pick the right grow lights for your greenhouse, plus our recommendations for you!
Why are grow lights necessary for greenhouses?
It comes as no surprise that plants can’t grow without light. Plants need light to photosynthesize, which allows them to convert light, oxygen, and water into energy needed to grow and develop.
But not all light is created equal. The chlorophyll in plants is responsive to particular wavelengths of light, absorbing the maximum light when exposed to red and blue lights, or light in the range of 400-700 nm. Green light, roughly in the middle of this spectrum, is not as easily absorbed, but this allows it to penetrate deeper into leaf tissues.
We don’t recommend using household light bulbs to grow your plants. While incandescent light bulbs are cheap and provide a continuous light spectrum, they would need to be placed far from plants as they can emit too much heat and burn leaves. Furthermore, the average lifespan of around 1,000 hours makes them highly inefficient.
On the other hand, the blue light emitted by fluorescent bulbs encourages bushy growth from plants, making them an attractive option. They’re generally cooler and more energy efficient than incandescent light bulbs. However, neither incandescent nor fluorescent lights are the ideal choice for efficient and healthy plant development.
Grow lights are specifically designed to meet the light spectrum needs of plants for all stages of growth, making them the most efficient choice for the greenhouse grower. Whether you’re starting seedlings or hoping to grow fruits and vegetables throughout the winter, grow lights are a must-have greenhouse accessory.
Different types of greenhouse grow lights
In order to pick the right greenhouse grow lights that will meet your specific needs, you’ll need to understand what you’re looking for. Knowing more about lighting is a big plus, but there’s a lot of information out there, and not all of it is easy to understand.
So, let’s break it down. First, there are three different kinds of bulbs commonly used as grow lights:
- T-5 bulbs are full-spectrum fluorescent lights that are capable of giving an efficient and high output of light. They use less power than incandescent lights and can serve up to 50,000 hours.
- HID or High-Intensity Discharge bulbs can provide the efficiency you need especially when you plan to plant over a wide area. However, they have to be installed at a distance as they can get hot and cause leaf burn. There are two kinds of HID bulbs: high-pressure sodium and metal halide.
- High-pressure sodium (HPS) bulbs emit red light that’s best used to encourage flowering and budding.
- Metal halide bulbs, on the other hand, emit blue light that stimulates bushy plant growth.
- Light-emitting diodes, or LEDs, are no longer the new kid on the block. In many cases, they’ve superseded other types of grow lights. They offer a balance of performance, energy efficiency, and lifespan. LEDs come in blue and red colors, give off little to no heat, and are more energy efficient. The average 11-year life span of LED bulbs is budget-friendly and adds to their allure.
What to look for in greenhouse grow lights
Besides the type of light bulb used in a grow light, there’s a number of other important aspects to look for when picking grow lights for your greenhouse. While there are a lot of grow light products out there, not all are designed to meet the demands of a greenhouse.
Greenhouse grow lights should be long-lasting, energy-efficient, and cover a wider area than grow lights designed for houseplants. Additionally, greenhouse grow lights should have the option to be used alone or daisy-chained together to easily and efficiently cover wider areas.
Are grow lights waterproof?
It’s important that the grow lights you choose for your greenhouse are waterproof, as you’ll be watering your plants frequently and humidity can remain relatively high in the greenhouse. Grow lights that aren’t properly sealed can start malfunctioning when exposed to too much moisture, and that’s the last thing you’ll want to deal with.
Fortunately, grow lights designed specifically for use in greenhouses are usually waterproof or at least highly water resistant.
Still, make sure to check the description for keywords that indicate the product is waterproof and/or able to withstand high moisture levels.
How much surface area do grow lights cover?
Another aspect that you should consider when looking for grow lights is how much surface area they can cover. If you’re trying to provide light to your entire greenhouse or multiple shelving units, you’ll want to calculate the total surface area so you’ll know how many lights of a particular model you’ll need.
Watts are generally a good indicator of how much surface area a grow light will cover, though it’s not one-size-fits-all. Higher wattage generally indicates that a grow light can cover more space at a greater distance from the plant canopy. However, more is not always better as too much light can actually burn your plants.
Additionally, LED lights operate more efficiently than traditional grow lights, so you can get the same amount of light for fewer watts. Often manufacturers will distinguish between displayed vs. actual wattage for this reason. For instance, a single LED grow light might use 25 actual watts, but give off light equivalent to a 50 W HPS grow light. Both lights will provide enough light for approximately 1 square foot, but the LED light will do so more efficiently.
How far to place grow lights from the plant canopy?
When it comes to grow lights, not all are created equal. Grow lights with higher wattage are generally more powerful and emit more light, but we also know that LED’s are more efficient at lower wattage. That said, you can use the “displayed wattage” of an LED grow light to figure out how far away you can place a grow light from the plant canopy.
To help you get started, here’s a general rule of thumb:
- 100 W = 8 -12 inches away
- 200- 399 W = 12- 20 inches away
- 400- 599 W= 20- 30 inches away
- 600+ W = 30+ inches away
For best results, make sure to monitor your plants at various distances. If a plant appears to be leggy or stretching towards the light, you’ll need to move the grow light closer. If, on the other hand, you observe leaf burn or bleaching, you’ll need to move the grow light farther away.
What about low-light vs. full-sun plants?
If things weren’t complicated enough already, you’ll also need to consider the needs of individual plants when choosing and placing your greenhouse grow lights.
Low-light plants such as tropical houseplants or leafy greens don’t need as much direct light to thrive. You can either place grow lights farther from the plant canopy and/or reduce the amount of time a grow light is on during the day.
Sun-loving plants such as tomatoes, on the other hand, might need as much as 12-16 hours of bright light close to the canopy.
Group plants with similar light requirements together so you can adjust your grow lights accordingly. For example, raise grow lights farther away from the plant canopy for low-light plants, or closer for plants requiring full-sun conditions.
You can even set grow lights on a particular schedule using a timer such as this one.
Are different grow lights necessary for different plant stages?
Plants benefit from different light ratios at various points in their life cycle. For instance, seedlings perform best with more blue light, while plants need more red light when developing blooms and fruit.
Many greenhouse grow lights offer a balanced “full” light spectrum that can meet the needs of all plant stages. That said, some grow lights can toggle between different modes (for example, red light vs. blue light) to enhance leafing or blooming as needed.
For most hobby greenhouse growers, it’s not necessary to buy and install different grow lights. If you want to switch between different light colors, simply choose a single grow light with those modes. For most purposes, however, a full-spectrum grow light supports healthy plant growth at all stages.
Picking the right grow lights for your greenhouse
Grow lights are a necessity in your greenhouse if you want to continue growing during winter when light is scarce. With so many different grow lights offered on the market today, it can be difficult to choose the right one for your greenhouse.
To help you pick the right grow light for your greenhouse, we’ve narrowed it down to our top choices for germination, flowering, vegetation, and budget.
Best choice for seedlings: MARS HYDRO TS-1000 Led Grow Light
This square, 3ft x 3ft LED grow light is perfect for starting seeds indoors or in the greenhouse. It boasts full spectrum light with high efficacy in the blue and red ranges, with blue light being more important for germination and early leaf development. The 120° refraction angle ensures wide coverage, but to cover more area you’ll need to daisy-chain multiple lights together.
- 150 W
- PPFD: 343 umol/m2s@12
- Full light spectrum (730-740nm Red IR/3200-4200Knm/5200-6800Knm)
- Light-weight at 3.7 lbs
- Max coverage is 3ft x 3ft
- 120° refraction angle ensures good coverage
- You can daisy chain up to 60 lights together, great for a medium-sized greenhouse
- There is an adjustable 0-100% dimming feature
- Ideal height from canopy for germination: 12”
- 5-year product warranty
Best choice for healthy blooms: Illumitex Eclipse GEN2 LED Grow Light
Get your plants to produce large, healthy blooms with the Illumitex Eclipse GEN2 LED grow light 4ft bar. The slim design allows for easy connection of multiple lights (up to 15 lights on a single power source), providing bright, uniform F3 spectrum light. The primarily red and blue wavelength is ideal for all stages of plant growth, especially once a plant starts flowering.
- Full F3 light spectrum
- Light-weight at 6 lbs
- Coverage: around 3.5 sq. ft. at 12”; 11 sq. ft. at a 26”
- Special design with 50° beam angle ensures maximum light distribution
- Can be chained together with up to 15 lights using the included 9-foot long power cord
- Internal dimmable driver (0-10V)
- Dust-resistant, waterproof, and damp-proof
- 5-year product warranty
Best choice for vegetables: AntLux 4FT LED Grow Lights
If you’re looking for an affordable, effective grow light for your greenhouse to overwinter vegetables such as leafy greens, the AntLux LED grow light could be a great option for you. This grow light comes in a pack of 4 and you can daisy chain up to 10 together on a single power source to light up an entire small greenhouse.
- Mainly blue and red light spectrum
- Each light weighs about 3.4 lbs
- Coverage: about 16 sq. ft. at 8”; 27 sq. ft. at 12”; 41 sq. ft. at 16”
- Integrated light reflectors reduce light loss and provide excellent heat dissipation; ideal for all kinds of flowers
- Daisy chain up to 10 together with a single power source
- Comes with mounting/hanging hardware
- 5-year product warranty
Best choice on a budget: Monios-L T5 Grow Lights
If this is your first time buying grow lights for your greenhouse, and you don’t want to invest too much, the Monios-L T5 LED grow lights are incredibly affordable and still highly effective. These come in a pack of 6 and can be daisy-chained together, though if you want to set up more than this you’ll need multiple power sources.
As you would expect from a budget grow light, these boast no fancy features such as dimming, but the full spectrum light will still support healthy plant growth at all stages.