Sales Hotline +1 (855) 904-4090
Cannabis Grow Lights - The Ultimate Guide

The Ultimate Guide for Cannabis Grow Lights

Intro to cannabis grow lights

Growing cannabis indoors provides the opportunity to control every part of the plant’s growth and to get the best results possible. One of the most crucial parts to consider is the lighting for the plants. For beginners, figuring out the right lights to use can be difficult because many options are available. Lights are needed to help create better yields and improve the crop’s quality, so it’s important to understand the options, the differences, and the best choice for beginners and more experienced growers. 

There is no right answer for which grow light is the best, but that doesn’t mean that beginner growers can choose just any lights to use. It is important to understand the different options, determine the plants’ goals, and figure out which lights will help the grower reach those goals. Learning about the different lights does involve a little bit of science to understand how lights help plants grow, but the right choice can make a huge difference in the crop harvested from the plants. 

What are Grow Lights?

When growing cannabis outdoors, natural light is used to help the plants grow. When plants are grown inside, they need more than just the lighting that’s already in the room. While the lights help illuminate the room, they don’t provide everything that the sun provides, which means they won’t offer everything that plants need to grow. Plants actually need a lot more than just light – they need the correct light to be able to thrive. 

Grow lights, on the other hand, are used to help cannabis plants get everything they need to grow faster, be healthier and have a higher yield. Grow lights can come in a variety of options and many different forms, so there’s an option for everyone and something perfect for any grow room.

Along with using grow lights for indoor operations, they can be used in greenhouses as well. Since greenhouses do have natural light throughout the day, grow cannabis lights are generally used to make the light cycle the right lengths and to provide benefits that may be missing from the natural light depending on the amount of shade the greenhouse receives for that time of the year. For instance, with the right greenhouse grow lights, it’s possible to have the correct lighting to grow even when it’s winter and daytime is naturally shorter. 

Why are Grow Lights Important?

Plants are not going to grow if they don’t have light. Cannabis, like other plants, uses photosynthesis to create energy and food, which sustains the plant’s growth. Outside, the natural light cycle determines when the plants germinate, how they grow, when they flower, and what they produce. Changes in the environment, such as changing to winter, can impact how the plant grows and whether it makes it to the end of its growing season.

Indoors, cannabis plants require quality light, just like they do outdoors. More light leads to larger plants and higher yields. Without light, the plants can’t produce the nutrition they need to grow, which will lead to stunted plants that don’t produce as much, if any, marijuana in the end. For cannabis plants, the more light that’s available, the better the plant will grow. While the plants need the right temperature, humidity, nutrients in the soil, and other factors, light is a crucial component that will make a difference in how the plant grows. 

The lights typically used in homes don’t offer the full spectrum of light, nor are they bright enough to help plants grow to their full potential. This is where grow lights make a difference. No matter what type of grow light is chosen, the lights will help the cannabis plants grow larger and produce much higher yields. They also make it easier to control the light cycle, dictating how large plants grow before starting to flower and when the flowering cycle begins. 


Photosynthesis is how plants convert light into energy to help them grow. This is a part of photobiology, which studies how the light interacts with living organisms like plants to help them grow. Light is electromagnetic waves that can have different wavelengths or frequencies. These can impact how much energy is carried by each packet or photon. For instance, visible light occurs when photons are created by electrons doing from one energy level to a lower one. For artificial lighting, the voltage determines the heat, which emits photons and creates the light we can see.

For growing plants, including cannabis plants, photosynthesis can only occur when light is present. Plants generally use the same wavelengths that we can see, and changing the wavelengths or frequencies of the light can impact how a plant grows. Within the light, certain colors will be absorbed easier by the plants, while others will not be absorbed as easily. Green light is reflected back off the plant, for instance, which causes the leaves to look green. Different colors can also impact how cannabis plants grow, with blue light impacting the plant’s growth and red light impacting the plant’s production. White light includes all of the colors, meaning it is a full-spectrum light. Depending on the grower’s goals, this may or may not be the best option for grow lights. 

Grow Light Types

Grow lights come in a variety of shapes, sizes, and setups. There are different types of light available, as well as different fixtures to consider. This is where determining what grow lights to use for your cannabis plants can be a little confusing. First, it’s important to determine if the grow lights are needed for indoor growing or for inside a greenhouse. It’s then necessary to consider the setup, the amount of light needed for the plants, and where the lights will be placed to benefit the plants the most.

Indoor grow lights are often different from greenhouse grow lights because of the environment they’re used in. Greenhouse grow lights might require different types of fixtures to allow them to be used in the greenhouse, while indoor lights can use almost any type of fixture. Before looking into fixtures, figure out where the plants will be used and what type of bulb will be used. 

How large is the grow room going to be? Smaller areas may do better with HPS or fluorescent lighting. The options are more plentiful for larger areas, so growers will need to consider which type of bulb is better for their situation and for the goals they have for the plants. It is important to consider how much light the plants need and plan for the correct amount of fixtures in the space to provide that light. For cannabis plants, err on having too many rather than not enough since more light is always better. 

Grow Lights for Cannabis

All indoor cannabis plants can benefit from grow lights to ensure they have the correct light for their needs. Some grow lights are created specifically for cannabis plants, however, and are designed for indoor setups. Lights designed specifically for cannabis will have everything the plant needs to grow and can take some of the guesswork out of deciding which fixtures or bulbs to use or how much light the plants need.

Something many growers do today is create or purchase a grow box that’s designed for cannabis plants. The grow box will include lighting as well as other factors that can impact the lighting, such as reflective surfaces. This helps contain the light in the area where the plant is growing, which enables the plant to use more of the light as it grows. With a grow box, it’s possible to get larger plants that have higher yields since it’s easier to ensure the plants receive the light they need. 

A grow box also helps to contain the plants, which can provide a number of other benefits as well. Since the cannabis plant is contained entirely within the grow box, there’s no need to worry about light leak or whether the plants will get the full amount of darkness they need during the flowering stage. This helps control the lighting further, which can help the plant grow and lead to a much higher yield in the end. They’re also easy to use and, since everything is controlled, the grower doesn’t have to do as much to grow marijuana at home. 

Light Sources

While almost any fixture can be used for grow lights, the bulb used is important to consider. There are a variety of different bulbs that are easily accessible, and that provide the light cannabis needs to grow. Those who are getting into growing at home will want to consider the best bulb type for their situation, then look into the right fixtures to work with those bulbs. Popular options for bulbs today include CMH, HPS, and LED. 

Understanding the differences between light sources can help growers make the right decision for their plants. When comparing the options, it is important to consider not only the benefits it provides for cannabis plants but the cost of the bulb, whether special fixtures are required, and the operating cost for each type. Some use more energy compared to others, so they’re going to be more expensive to operate even if they cost less initially. Growers should make sure they consider this as part of their budget for growing, as this can help impact the decision on what light source to use. 

Ceramic Metal Halide (CMH)

Metal halide lights create light by pushing an electrical current through a mix of mercury gas and a metal iodide. The vaporized mercury and metal iodides are contained inside an arc tube, so they are safe to use. In the past, quartz was used for the tubes, but newer options offer a ceramic tube. These are said to be more efficient than the quartz tubes and will have a more balanced spectrum of light. 

CMH lights are often used as the primary light source in grow rooms or as supplemental lighting in greenhouses. Many of these lights are more on the blue end of the light spectrum, so they can help with vegetative growth. The blue part of the spectrum can help plants grow, as well as help produce more lush foliage, leading to more buds on the plant.  

Metal halide lights have been used by cannabis growers for many years now and are still a good option for growing indoors. However, fewer growers are using these lights today because there are better lights available, and they do require more energy, which leads to higher power bills. Still, growers who want to choose a bulb that leans more toward the blue end of the spectrum can pick up CMH lights and try them out to see what effects the light will have on their plants. 

High-Pressure Sodium (HPS)

During the 1980s, more growers started using HPS lights instead of the metal halide lamps. Though these lights have been used for years in various applications, they weren’t commonly used for grow lights until it was discovered that growers in Europe were using a lot less energy compared to growers in America. The main reason for the discrepancy, and the switch to HPS lights in America, was because HPS lights use a lot less power compared to CMH lights. 

HPS lights work similarly to CMH lights, except they use a combination of mercury and metallic sodium inside the tube. This makes them far more efficient, which caused them to become used more frequently for grow rooms. These lights are shifted more toward the red end of the spectrum, which helps with flowering. These lights are powerful, so they need to be further away from the plants compared to the CMH lights.

Though they are likely a good option for growers today, they can’t be used with shelf configurations in the grow room because they need to be further away from the plants. They create heat, so plants that are too close, especially seedlings, will end up burnt. They’re also less efficient compared to other types of lights, like LED, and the light output will drop over time. In fact, for these bulbs, it’s best to replace them at least once per year. There is always a potential for the bulb to explode, though instances of this happening are rare. Still, it’s something for growers to know about if they are considering using HPS bulbs for the grow room. 

Light Emitting Diodes (LED)

LED lights are promising for grow rooms, thanks to the new technology being used to improve them for most uses. They are low voltage, so it will cost less to use LED lights compared to other light sources. They also don’t produce a lot of heat, so there’s no need to worry as much about fans and ventilation. These lights aren’t going to burn the plants, so they are perfect for shelf configurations where the light must be close to the plant. 

LED lights use voltage to cause photons to move across a junction created by semiconductor materials. This creates a light that includes a range of wavelengths, so the colors do look well-defined to the average person. It is possible to use LEDs to create a variety of colors with lights, and many have phosphors on the blue LEDs to create white light. The variety in which this can be adjusted means there are LEDs that have been created to help plants absorb more light. This creates a somewhat purple light, which tends to be the best light for growing cannabis because of how the plants respond to the purple wavelengths. 

The main benefits of LED lights are the price point. In recent years, they’ve become far more efficient to produce, so the price has dropped significantly. Anyone can afford LED lights now, though those that create a specific wavelength may be more expensive compared to ones that are focused on just creating white light. They also consume a lot less power compared to CMH or HPS lights, so they’re going to be less expensive to use, and they last a lot longer. This means LEDs are often the go-to choice for today’s growers. 

Grow Lights for Cannabis

White Light Versus Purple Light?

White light is known as a full-spectrum light, as it contains all of the various colors. There are also lights that tend to be bluer or redder, depending on the wavelengths created by the light. Another option is purple, which is a combination of blue and red wavelengths. Purple lights can tend to be bluer or redder, but they do have benefits beyond what white light can offer.

Blue lights are able to help plants grow, which is great for the vegetative stage. Rend light, on the other hand, helps with photosynthesis and can help lead to more flowering. For cannabis plants, both of these are needed, which is where purple lights can help. Combined together, the plants will get everything they need to stimulate the growth patterns of the plant, helping them grow larger and have higher yields.

Purple also helps the plants know when to rest and when to gather more light to use. This helps fix the issues plants have when they don’t have sunlight to help them grow. Still, growers do have options they’ll need to consider. They’ll want to choose a darker purple color or a lighter purple depending on what they want for their plants. Darker purple can help lead to taller plants, while lighter purple will lead to better buds. There are also white lights combined with the purple lights, which can provide additional wavelengths that the plant can benefit from. 

Daylight Lighting Versus Artificial Lighting

Sunlight, when there is enough of it, is an excellent source of light for cannabis plants. The sunlight should be direct, not filtered, and should last for 10 to 12 hours a day for the best results. This does mean, however, that plants may not get enough sunlight during the winter months, even if the temperature is okay for outdoor growing. Sunlight, however, is free, so when it can be used, it is the best light source for marijuana plants. 

It is necessary to choose the right site for any plant that will be grown in natural light. It is important to make sure the plants get as much sun as possible. Filtered sunlight and shade need to be avoided, as the plants won’t get everything they need from the sunlight. Even in the right location, however, cloudy days can mean the plants aren’t getting all of the light they need, which can make a difference in how well they grow. On top of this, with outdoor growing, it’s difficult to control everything, including weather that can damage the plants. 

Though natural light does have everything the plant needs to grow, artificial light sources are able to mimic natural light well, providing the benefits of the various light wavelengths without the plants needing to be inside. Those who use lights in a grow room are able to completely control the environment, including the type of lights the plants receive. Growers can change how intense the lights are, which wavelength or color is more prominent, the distance between the light and the plant, and more. The controlled environment makes it easier for growers to reach their goals and allows them to adjust as needed to get higher yields from their plants. 

Photon Pigment

Cannabis plants react to the light they receive, with various photomorphogenic reactions possible through the plant’s lifespan. White lights are measured by the color temperature. Those with a lower temperature have a yellow tint, while those with a higher temperature have a blue tint. No matter what the temperature is, the white color does include the full spectrum of light, and the cannabis plants respond to different colors with changes in their growth cycle. For instance, the change in growth cycle because of photon pigments happens when seeds germinate and when they switch from the vegetative to the flowering stage. 

Full-spectrum lights will often come with red and blue settings, which can help change the light that the plants see and impact what growth cycle the plant is in. When growing cannabis, blue can be used for the vegetative growth state to encourage more growth, and red can be used to signal the change to the flowering stage and support the buds as they grow. With sufficient light for each plant, these changes can be timed to help the plant reach its full potential, something that can’t be done with natural light. 

Red lights

Red wavelengths are known to help regulate growth in marijuana plants. When used during the vegetative stage, red lights can create taller marijuana plants with longer stems. It can also help with photosynthesis, so the plants obtain more energy while they’re growing. During the flowering stage, red lights help boost the growth of the flowers, which can lead to better buds and higher yields.

Blue lights

Blue lights are helpful in regulating growth in cannabis plants. The blue wavelength can lead to shorter but thicker plants that have shorter stems. The leaves are much larger compared to plants that receive more red light during the vegetative stage and are likely going to be a darker green color. Though plants with higher amounts of blue light may be shorter, they are often healthy and will end up producing more than plants that are taller but thinner. 

Both blue and red lights can be used throughout the cannabis plant life cycle to help impact how the plant grows. Growers who prefer more compact plants may want to focus on blue light during the vegetative stage, then switch to red light during the flowering stage to produce better buds. It is possible to have blue and red lights while the plant is growing, as well, so the plants are able to produce more energy and be as healthy as possible. This is done using purple lights, which can still lean toward a bluer or more red light, depending on the light source and the grower’s preferences.

Growers can purchase lights today that have both blue and red options, as well as white, so they can experiment with color combinations and figure out what works best to help them reach their goals. It’s also possible to adjust other factors, such as how close the light is to the plant, to impact how much photosynthesis can be done by the plant and how much energy is then created for the plant to use. 

Lighting Cycle for Cannabis

Just getting the right lights isn’t enough to create a higher yield, though it does help. It’s also crucial to understand the light cycle for cannabis and what lights need when they’re growing. A lighting plan can help create a better yield, as it helps control when most marijuana plants switch from the vegetative stage to the flowering stage and how much energy the plants receive through photosynthesis during each stage.

When it comes to creating a light cycle for indoor plants, it’s important to know what the plants need during the different stages. During the vegetative stage, plants benefit from long daylight hours. In general, growers should have the lights on for at least 18 hours during the vegetative stage, though some may want to leave the lights on 24 hours a day. The vegetative stage should last for around two months, though it’s possible to keep marijuana plants in this stage for longer by simply keeping the lights on the same schedule.

After two months, it’s time to switch to the flowering stage. Marijuana plants know when it’s time to switch based on the change in light hours. For the flowering stage, the lights should only be on for 12 hours per day. For the rest of the day, the plants should be in complete darkness. This tells the plants to start producing buds and gives the plants the rest they need from the light while they’re flowering. Check out more information on the lighting cycle now. 

Maintaining Optimal Lighting

Though sunlight is optimal for cannabis plants, it’s not possible to use the sunlight indoors, and throughout the year, so artificial lighting will be needed. To maintain the optimal lighting for plants, it’s important to use the right color lights, the right type of lights, and the right light cycle

To start, blue light is better for the vegetative stage of growth. MH lights provide more blue light, making them a good option for this stage, even though they can draw more power and, therefore, be more expensive to use. The blue light is what the plants receive more of during the middle of the summer, as the sun is further away. When the plant moves into the flowering stage, it’s better to use red light. This mimics the light plants would receive at the end of summer when the sun is closer and the daylight hours are shorter. HPS lights can be a good option during this time, as they offer more red light.

The distance of the light should be carefully considered. Depending on the wattage and the type of light, the light source can be closer or further from the plant. For MH and HPS lights, increase the distance from the plant to the light based on the amount of wattage since higher wattages will produce more heat. LED lights can be placed closer to the plants, but there is still an optimal distance. It often takes trial and error to figure out the best distance to make sure the plants receive enough light. If the plants seem to be reaching toward the light, they’re likely not getting enough light. The light source, in this instance, should be moved a little bit closer. 

Once the lights are set to the optimal distance, and the correct light source is chosen, make sure the lights are positioned correctly. The light should shine on the plants, not the area around the plants. If the plants look like they’re burning, it’s not that the lights are positioned incorrectly. It’s that the light source is too close to the plants. The light source will need to be moved as the plant grows to help prevent this. By learning more about maintaining optimal lighting, however, it’s possible to figure out the right settings, to begin with. 

Lighting Cycle

The light cycle is necessary to get right throughout the time the plant is growing, as it does impact how large the plant grows and whether it switches to the flowering stage. Autoflowering cannabis plants are the exception, as they’ll start flowering at the right time no matter if the light cycle changes or not. For most marijuana plants, however, the light cycle should be set to at least 18 hours on and no more than six hours off once the plants have started to sprout. Once the seedlings have appeared, the plants enter the vegetative stage and need as much light as possible. For maximum growth, the lights can be left on 24 hours per day. 

Other than Autoflowering plants, cannabis plants will start flowering when the light cycle changes to 12 hours on and 12 hours off. It is important to make sure that the light is not on for any longer than 12 hours, as the plant may not start flowering. Once the lights are switched, so the plant starts to receive at least 12 hours of darkness per day, the plant should begin flowering. From there, it won’t be long until the buds are ready to be harvested. 

Cannabis Grow Lights - The Ultimate Guide

Best Grow Lights for Cannabis

Determining the best grow lights for cannabis isn’t easy to do, simply because everyone is different. Growers who have different setups or different goals for their plants may prefer one type of light source compared to other growers. It is important to consider a variety of factors, including the type of light source, the color of the light, the stage the plant is in, and more to determine the best grow lights for cannabis.

Since the plants will be grown indoors, it’s best to pick out options that best mimic natural light and will provide everything the plant needs to grow. For this, growers can choose from any of the light sources mentioned previously. Today, LED lights are growing in popularity as they provide a plethora of options, can include lights that switch between blue or red light, are cooler than other light sources, and are becoming less expensive. Still, many growers do opt for other lighting sources, as it may fit their needs better. 

To start, growers need to consider the space where they’re growing cannabis, as some lights are better for large areas compared to others. Someone who may be using a grow room, for instance, may opt for CMH or HPS lights, as they can provide the right light for cannabis plants, but they do get hot. A larger room gives more space for the heat to dissipate, so it’s easier to keep the plants at the right temperature. Someone who is using a grow box, growing in a closet, or in a similarly small place may opt for LEDs instead, as these don’t produce as much heat. Take a look at more information on the best grow lights for indoor growing now to figure out which lights might be perfect for trying. 

Comparing Cannabis Grow Lights

Growers do have a variety of light sources, with pros and cons to each of them. For many years, CFL bulbs were the choice for growers because they were easily accessible. Unfortunately, a lot of these lights are needed to mimic natural light properly, so they get expensive to run and lead to higher power bills. These are still a good option for heat-sensitive plants like weed seeds that have just started to grow or cuttings that are growing roots. 

High-intensity discharge lights are very powerful, so they work well for growing marijuana. Metal halide and High-pressure sodium vapor lights are types of HID lights that growers commonly use. As mentioned previously, these do tend to be redder or bluer, depending on the type of light, and do produce a significant amount of heat. HPS lights also require more power, meaning they cost more to operate in the long run. 

LED lights offer lower voltage, so they can be a great option for many growers. They’re low-heat, so they can be used for seedlings as well as flowering plants. They are also less expensive to operate, saving the grower money in the long run. Today, there are many different options for LED lights, so many growers choose them simply because of their affordability. Before buying any lights, however, get more information about comparing cannabis grow lights

Figuring out the right grow lights to use can be a little complicated and can require some trial and error. However, it is best to start thinking about what lights will be used before selecting weed seeds to grow, as this allows growers to make sure they’re ready to start when the seeds arrive. Growers today have more options available to them than ever before, along with better knowledge of what marijuana plants need while they grow. They have the ability to pick out lights based on where the plant is in its lifecycle, the size of the room the plants are growing in, the desired outcome for the plants, and a lot more.

If you’re ready to start growing marijuana, use the information here to figure out which lights are best for your situation. It may be necessary to play around a little bit with where the lights are located or how long they’re on each day, but you should be able to quickly figure out the optimal lighting requirements for your plants and make sure they continue to be as healthy as possible. This will help increase your yield, as well as make sure you’re growing the best marijuana possible. Once you have the lights figured out, check out the full grow guide below to get more information and make sure your first or next crop will be successful. 

AUTHORED BY: magento

This website is exclusively for individuals who are of legal adult age (21+).

By selecting ENTER, you verify that you are 21 years of age or older.