Whether you’re starting your indoor cannabis garden or simply updating it, grow lights can make or break your efforts. There are dozens of brands on the market, and every brand has different sizes and models to choose from. There are also dozens of factors that can affect whether a certain grow light is really a good choice for your setup. With all these variables, making an informed choice might seem impossible.
It doesn’t have to be that difficult, however. By comparing your most common options, you can make an informed decision that takes into account your personal growing situation. Cannabis plants rely on light for nourishment and for growth cues. What kind of light and how much your plants need will change throughout their life cycle, so it’s important to understand those needs if you want a great harvest.
When you’re germinating seeds and growing seedlings, it’s best to have light on them for at least 18 hours a day. There is a lot of debate about whether seedlings should be lit 24 hours a day, but either way, constant light is key to having healthy plants from the get-go.
However, you don’t want the light to be too hot or too bright. Seedlings are delicate, so it’s important that you don’t burn them. They also prefer a cooler light color, because blue and ultraviolet light fuel vegetation growth. Lights that can be dimmed and don’t produce a lot of excess heat, like LEDs or CFLs, are great for seedlings.
Cannabis plants remain in the seedling stage for 2 to 4 weeks.
Once your plants have 5 to 7 parts to each leaf, they graduate from seedlings to the vegetative state of growth. This is the time when your plants are growing as much greenery as possible, so they have lots of places from which they can flower and lots of leaves to fuel flower production.
During the vegetative stage, keep lighting your plants for 18-24 hours a day. However, you can turn up the brightness of your lights now. Plants in the vegetative stage are less delicate, so they can handle brighter light and warmer temperatures without burning. Keep the light on the blue side, to fuel healthy greenery. LEDs and LECs are great for the vegetative stage.
Plants stay in the vegetative stage for 2-3 weeks, depending on your strain.
Your plants begin flowering when you change their light cycle. To start or “trigger” the flowering stage of your cannabis plant, change your light routine to 12 hours of light a day and 12 hours of dark. This mimics the natural change of the seasons, which leads to flower production in cannabis plants.
Flowering cannabis plants need more red light and less blue. Red light encourages flowering, while too much blue light will divert some of your plants’ energy away from flower growth and into continued vegetation growth. Lights like HPS lamps and LEDs are good choices for the flowering stage.
LEDs vs CFL vs LEC vs HPS vs T5
The first step to choosing the best grow light for you is to understand the differences between the different types. Each grow light type has pros and cons, so be sure to keep your budget and grow tent setup in mind when you’re considering whether a given light is the right choice.
LED Grow Lights
LED stands for “light-emitting diode,” and if you couldn’t tell from that name, LEDs are the most technologically advanced grow lights out there. Only recently have LEDs become practical for anyone other than industrial growers. The recent advancements in LED technology have brought these lights into the price range of even the smallest cannabis producer.
LEDs are one of the best choices for grow lights, regardless of the size of your crop. An average LED can last upwards of 50,000 hours of use, which is at least triple that of any other grow light. They’re also energy-efficient, keeping your electric bill down every month. Many LED lamps are even recyclable. The only real downside to LEDs is that they still cost more upfront than other light options, because of the technology needed to manufacture the circuits.
They can come in every color of the rainbow, as well as ultraviolet and infrared. This makes them perfect for use as grow lights. Their intense light production and the sheer amount of the light spectrum that they cover means that they are equally useful for the seedling, vegetative, and flowering stages of cannabis growth. So, how do these grow lights make it happen?
How Do Full-Spectrum LED Grow Lights Work?
LED grow lights work by combining electrons and electron holes in a semiconductor. Electricity flowing through the substance causes electrons and electron holes (really just atoms with a positive charge, meaning that they can accept another electron) to interact and emit light. This makes LEDs much more energy-efficient than other forms of light-production because there are fewer steps needed to convert electricity into light.
There are many ways LEDs can be built. The two most common varieties used in grow lights are Surface Mounted Device (SMD) and Chip-on-Board LEDs aka (COBs). Between the two, SMDs are usually slightly cheaper, because they can fit fewer diodes per square inch due to their construction. They can change color within the visible spectrum, as well, because each diode has its own circuit and can be controlled individually.
Meanwhile, COB LED grow lights are more expensive because they can fit many more LEDs per square inch. In fact, COB LED grow lights usually appear as a single flat panel, instead of many individual lights. They ‘re also brighter and use more electricity than SMDs, because of how many diodes they have. COB LEDs cannot change color, because they have only one circuit per unit.
Each LED typically produces one color of light at a time. This color is determined by the “width” of the “energy band” that electrons must cross to reach electron holes. LEDs can be designed so that they only have one possible energy band and color, or they can include an on-board chip that allows the energy bandwidth, and therefore the color, to be changed.
Often, white light is produced by LEDs either placing bulbs producing red, blue, and green close together, so the light appears white to the human eye. The other option is for the diode to include some type of yellow phosphor coating. In this case, the LED grow light emits blue lights, which impacts the phosphor and triggers a further release of yellow light. In this case, the yellow and blue light again combine to form white light.
Full-spectrum daylight equivalent LED grow lights often combine a variety of different LED types. They often include some LEDs dedicated to UV and IR light, along with many dedicated to the visual spectrum. The brightest LED grow lights often include both COB LED grow lights for the white light and smaller individual diodes for IR and UV light.
How to Compare LED Grow Lights to Choose the Best
When choosing an LED grow light, you want to keep three factors in mind: size, light color, and wattage. LED lights primarily shine on what’s directly beneath them. Every cannabis plant should have about four square feet of space, as a rule of thumb, so you want to have 2 or more square feet of light fixture per plant. This ensures even light coverage.
You also want to look for what colors of light the LED produces. Daylight is good, but it’s even better if the light has a switch or setting to change the light color from blue-heavy to red-heavy.
Finally, look for actual power usage, as well. Some LEDs list the watts a comparably bright HPS grow light would use, while others list their actual power usage. Either is good, as long as you know what you’re getting. Intensity is also measured in “lux,” which is how many lumens per square meter are measured at a certain distance away from the light. The higher the lux, the brighter the light!
- Pros: Energy efficient, low temperature, wide variety of options and price points.
- Cons: Higher initial cost than other systems of comparative brightness.
- Cost: Higher upfront costs, but long lifespan and energy savings more than make up for it.
- Average lumens per watt: Lumens are a bad measure of intensity for LEDs, but on average, 115.
- Growth stage application: Various
- When to choose: LEDs are great for when you know you’re planning on growing for a long time.
- How to set up: Most LEDs are plug and play – simply plug in and turn on the switch. Others include programming options, so you can time when your lights turn on and off, as well as what colors are on or off at a given time.
CFL Grow Lights
CFL lights are the curly white bulbs known for being energy efficient in your average 60 watt household socket. They can also be used as grow lights, if you’re only able to get what’s available at local shops.
These lights work by using electricity to excite argon and mercury gas. These gases, when excited, emit ultraviolet light. The white coating on the inside of the tube is a phosphor, which glows white when the UV light hits it. The white light from the phosphor is the light we see. CFL lights last about 15,000 hours, less than half the time of LEDS, but still greater than some other options.
CFL lights are usually the cheapest grow lights on the market, because of how common the bulbs are. They also stay relatively cool, which saves you money compared to lights like HPS or CMH grow lights. However, the light they produce is not as bright as other grow light options. As most CFL bulbs are designed to light homes with minimal electricity, they put out enough light for people to see comfortably, which is much less than a tropical plant needs to grow to its full potential.
They also produce light mostly in the blue-white part of the spectrum, which is not ideal for the flowering phase of cannabis growth.
Overall, CFL grow lights are great for if you’re just starting out with cannabis growth and you aren’t sure if you’ll stick with it. These lights also keep plants smaller, which may be a bonus if you’re growing in a confined grow tent or space.
- Pros: About as cheap as possible, easy to find, compatible with most sockets.
- Cons: Not very bright, not ideal for flowering stage, not recyclable.
- Cost: Low!
- Average lumens per watt: 50-70.
- Growth stage application (if not a full-spectrum light): Seedling and vegetative stages.
- When to choose: When you’re just starting out and might not continue.
- How to set up: Find a reflector with a 60-watt socket; something similar to a floodlight is great. CFL light bulbs are designed for standard sockets, so all you need to do is screw it in and turn it on. Any programming has to be done with extra gear.
LEC Grow Lights
LEC stands for Light Emitting Ceramic. These grow lights are related to metal halide lights, but use ceramic arc tube the same way HPS lights do. Compared to old metal halide lamps, they produce a more natural-appearing light and give off brighter light for the same amount of energy. They require a “ballast,” which is a circuit that regulates the current to your LEC light. Essentially, the ballast “pulses” the current in order to stimulate the ceramic arc tube. While some LECs come with a ballast, not all do, so pay attention to the description if you purchase one of these lights.
LECs are also called “ceramic metal halide lights” (CMH lights) and “ceramic discharge metal halide lights.” LEC is technically a trademarked term, but it’s beginning to go the way of “Google” and “Kleenex,” where people use the term to refer to any CMH light.
CMH grow lights are heavy on the UV spectrum, and produce a lot of UV-B light. If that term sounds familiar, you’ve probably seen it on your sunscreen: UV-B light causes sunburn in humans. It also triggers greater trichome production in cannabis plants. Studies are ongoing as to why this might be. The current hypothesis is that trichomes are produced to protect delicate tissue from harmful UV-B rays, and so more intense UV-B exposure results in more trichome production.
CMH grow lights last about 20,000 hours, while a CMH ballast can last for 50,000 hours. They generate a significant amount of heat, so make sure you have sufficient ventilation in your indoor space. You don’t want to burn or wilt your plants, after all.
- Pros: Produces UV-B, which can supplement red-spectrum lights to increase trichome production, relatively efficient.
- Cons: Generate significant heat, replaced more often than alternatives, not as bright as LEDs or HPS lights, not recyclable.
- Average lumens per watt: 90-105.
- Growth stage application: Seedling and vegetative, supplementary during flowering.
- When to choose: If you already have a ballast, or if you have HPS lights for the flowering stage, CMH lights can be a good choice.
- How to set up: Check to see whether your lights include a ballast. If so, it’s plug-and-play – otherwise, purchase a ballast to regulate lights so they don’t pop. Remember
HPS Grow Lights
Another option for a more analog light is HPS lighting. High-Pressure Sodium (HPS) lights are often used as floodlights and produce a strong yellow/red light. They work by using a ballast to oscillate the electrical current through the light. This pulsation energizes xenon gas in the light, which in turn energizes mercury vapor, which triggers the sodium gas. All three gases emit light, which combines into the warm-toned light we see.
This process generates a lot of heat, so good ventilation is important. Most HPS lights can be used indoors or out, so if you use extra lights on outdoor plants, you can bring them inside as long as you make sure your exhaust fans are up to snuff. These lights can last up to 24,000 hours, so it’s the second-longest lasting high-intensity light out there, after LEDs.
HPS lights do not produce much light outside of the yellow-red portion of the spectrum, so they’re not great for the seedling and vegetative stages of cannabis growth. HPS lights are some of the brightest lights on the market, however. If you are supplementing your plants with other lights that are heavy on the blue end of the spectrum, HPS lights can be a great primary light source.
- Pros: Heavy on yellow-red light to help flowering, very bright.
- Cons: Not great for the vegetative stage, hot, not recyclable.
- Cost: Low
- Average lumens per watt: 105-150.
- Growth stage application: Vegetative with blue-light supplementation, flowering.
- When to choose: If you don’t mind excess heat, or if you need to light a truly large space on a budget, HPS lights might be the choice for you.
- How to set up: Get your ballast plugged in first, and take any precautions.
T5 Fluorescent Grow Lights
Fluorescent lights are the long tubes often found in stores, hospitals, and schools. Because of this, they can often be purchased at well-stocked hardware stores, making them easier to get than anything but CFL grow lights. There are many fluorescent bulb diameters, which are designated “T#;” for example, T5, T8, and T12 are common. The number stands for the width – a T5 is 5/8ths of an inch wide, while a T12 is 12/8ths, or 1.5 inches.
Fluorescent lights work by vaporizing mercury, which creates UV light and in turn excites the phosphor that coats the inside of the tube. The phosphor is what gives off the light we see, just light CFL lights. Like most bright lights, fluorescent tubes need a ballast, which is usually sold separately and bumps up your startup cost.
An average fluorescent tube lasts about 16,000 hours, but the light quality changes towards the end of its lifespan. They’re typically cooler than HPS or CMH lights, but generate more heat than LEDs.
Some people find fluorescent lights to be annoying because in aging bulbs the ballast oscillates slowly enough that the flicker can be noticeable. Low-quality ballasts can also generate radio interference that affects other electronics and can be traced from a distance.
How to Choose and Set Up T5 Grow Lights
Fluorescent tubes are available in many lengths and colors, so you have plenty of options depending on the number of plants you’re growing. However, no one fluorescent light gives off the perfect spectrum of light to cover the whole growing season. What many people do is use “cool light” fluorescent light bulbs during the vegetative stage, and switch out to “warm light” fluorescent bulbs when it’s time to flower.
This is still simpler than using CMH and HPS lights together, though. You can use multiple lights of different colors in the same ballast, and changing them out is simple. Combining CMH and HPS lights requires installing two ballasts. You can set up a fluorescent grow light by installing a single ballast above your plants, and the tubes snap in and out easily to change them for different stages.
- Pros: Easy to find, easy to replace, cool.
- Cons: Short relative lifespan, requires changing bulbs for flowering,
- Cost: Moderate to low.
- Average lumens per watt: 90-105.
- Growth stage application: Different bulbs are good for different stages, but can use the same ballast.
- When to choose: If you have access to a fluorescent ballast, or if you want your lights to be easily replaceable, fluorescent bulbs can be a good choice.
- How to set up: Install the ballast and pop in the bulbs.
Fluorescent VS. LED: Which Is the Best Grow Light?
Two of the most common grow lights used by smaller cannabis producers are fluorescent and LED grow lights. These two types of light are usually chosen for their low heat production and simplicity.
Fluorescent bulbs are cheap and can be replaced easily. However, they last a quarter of the time of an LED grow light bay. They also aren’t as bright as LEDs per watt. LED grow light bays do have an upfront cost of purchase. However, compared to buying a fluorescent light fixture, lumen for lumen LED lights aren’t that much more expensive. Unlike fluorescent lights, you don’t need to replace LED bulbs for the life of the unit.
When you compare the two, if you’re looking for something that’s cheap upfront and only temporary (such as for one or two grows), fluorescent might be a good choice. However, if you’re planning on growing for more than a year, LED lights quickly and easily become your best option.
How to Calculate the Electricity Needed for a Cannabis Garden
Now that you have a good idea of what kind of grow light is good for your, you might want to know how much energy it’s going to use.
To figure this out, there are three important factors: the wattage of the lights, the time it will be on, and the cost of electricity.
Let’s say you’re running a 100 watt LED grow light for 12 hours a day. If electricity costs $0.05 per kilowatt (1000 watts), then you’re spending (100 watts x 12 hours x 0.05 per kilowatt) / 1000 watts = $0.072, or 7 cents a day.
However, if you’re running more lights, or running them for longer, this number can go up quickly!
What Will My Estimated Electrical Cost Be When Growing Indoors? Outdoors?
The safe rule of thumb is that you want to use about 100 watts per plant when you’re lighting your indoor garden. This means that you can estimate costs based on your number of plants.
Let’s do the math:
If electricity costs 5 cents per kilowatt, then using the equation above, for one plant you are looking at 11 cents a day during the vegetative stage and 7 cents a day during the flowering stage. This is $3.30 per month for the vegetative stage and $2.10 per month for flowering plants. Five plants would be $16.50 and $10.50, respectively, and 50 would be $165 and $105.
However, indoor cannabis gardens also use ventilation and other electrical appliances, so make sure you take this into consideration when you make your estimates! The same calculation applies for the wattage of air conditioning units, ventilation fans, and anything else you might be using to run your cannabis garden.
“Outdoors,” on the other hand, is a broad term. You can grow cannabis outside without any electricity at all, or you can use just as much as you do indoors, depending on your grow setup.
How Many Grow Lights Can I Put on One Circuit?
The number of grow lights you can plug into a single circuit depends on the amperage of your circuit.
Here’s the equation: Wattage/voltage=amperage
Now let’s explain that.
The number of grow lights you can SAFELY plug in depends on the wattage of the lights, the voltage that’s running them, and the number of amps that your circuit can safely handle.
Take the wattage off all of the lights you want to plug in and add it together. Three lights of 240 watts each is 720 watts that will be coming from your outlet.
Most types of indoor grow lights can be found in both 120 volt and 240 volt options.
120 volts is what most regular devices use, but with ballasts, you can plug in a device that will use 240 volts.
Finally, you can find a circuit’s amperage by checking the circuit breaker. An average American wall outlet has an amperage of 15, while a dryer outlet is 30 amps, and a new range outlet is 50 amps. You never want to use more than 80% of the total amperage of a circuit. Lights often use significantly more watts for the first couple seconds after they’re turned on, so if you use more than 80% and turn your lights on all at once, you can blow a fuse or even start a fire.
Let’s try plugging in those three 120 watt lights.
720 watts/120 volts=6 amps
No matter what circuit you’re using, that’s a safe number to plug in! Run this equation if you’re not sure what your circuit can handle, and you should be safe.
What Electrical Precautions Should I Take?
It’s better to be safe than sorry. If you’re not sure what you need to do, talk to an electrician before trying to set up your electrical systems yourself. Here are some basic guidelines to keep in mind when you’re doing any electrical work, related to your grow lights or otherwise.
- Always keep water away from electrical components such as plugs, wires, outlets, and anything else with a current.
- Never touch wet electric components. Turn off the circuit breaker and triple check before removing any components from water.
- Always turn off the breaker before doing any work on electrical components.
- Never use metal equipment when working with electricity.
- Be cautious with your circuits – don’t plug in too many things, or you could start a fire.
- Always make sure your equipment will cooperate. Make sure you don’t exceed outlet amperage and that any equipment is rated for the right number of volts for your area.
- Check for faulty wiring before plugging anything in.
- Don’t use extension cords – the more through which connections a current travels, the more likely it will be able to spark and start a fire.
- Keep cords organized neatly to avoid tripping hazards and broken wires.
- If you do blow a fuse, you must fix the problem that overloaded the fuse before you replace the fuse.
Remember, safety first! Happy Growing!