A Complete Guide To Grow Lights For Marijuana Plants

Last Updated on January, 2024 by Rob Wilson

Marijuana used to be a rather touchy topic in the past and stoners and growers used to be looked down upon. However, people’s attitudes have been growing increasingly liberal towards the consumption and sale of marijuana and hence laws have also adjusted according to the same. Most states in the US now allow consuming marijuana – at least for medicinal purposes. Some states even allow the consumption of marijuana for recreational purposes and licensed dispensaries have now started off where you can buy legal weed! However, there’s a different joy in growing your own weed. 

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One of the best ways to grow your own weed is to grow it indoors and one of the most important things that you need to grow marijuana indoors is a grow light. A grow light is as critical to indoor growth as the sun is to the outdoor growth. Over the course of this article, we shall be taking a closer and detailed look at what a grow light is and what are the benefits of using it. We shall also be taking a detailed look at the lighting requirement of plants across different stages of their growth cycle. 

In addition to that, we will also be taking an in-depth look at the different kinds of lighting options that there are – and lastly at full spectrum LED grow lights, and why they are considered better than all the other options. We shall then answer some frequently asked questions before concluding the article. So let us begin straight at the basics:

What is a Grow Light? Why Do You Need to Use It?

Normally when a plant grows, it needs the light of the sun in order to ensure that processes such as photosynthesis happen properly. This is a very crucial process for the growth of any plant because it helps the plant generate energy which helps it to grow. Apart from the process of photosynthesis, sunlight also helps the plants produce and secrete other compounds and enzymes such as chlorophyll which are very important for the overall well being of the plant.

Plants also grow on something called a ‘photoperiod’ – which is the number of sunlit hours they are getting. It is based on this photoperiod that a number of life events of plants are determined. First off, the shoot grows in the direction of the sunlight – this is just evolution playing its role which makes sure that the plant can get as much sunlight as possible. Then there’s flowering – when the lighting hours are naturally reduced, flowering also takes place. However, all of this happens in nature when you are growing your plants outdoors. What happens when you plan to grow your marijuana plants indoors?

When you grow indoors, the natural sunlight is replaced with the light that comes out of grow lights. The sunlight is white or yellow when you look at it. However, it is actually made up of different lights of different spectral wavelengths – consisting of the reds and the blues, which are the warm and cool type of lights. Grow lights provide the exact kind of lighting that a plant needs at the the stage of its growth to ensure that it grows properly. Grow lights are basically devices which replace the sun when you grow weed indoors.

There are a number of benefits of using grow lights. The biggest being they give you complete control over your plant’s growth. Given how important lighting is, being in control of lighting means you can create optimal lighting conditions which will help your marijuana plant maximize its yields, and grow taller and stronger. While you can’t do much to the sun’s natural light, grow lights can be turned on and off at a specific time – creating longer or shorter photoperiods based on your plant’s needs. Grow lights can also be moved closer or farther away from the plant based on the intensity needed. 

Furthermore, blue lighting can be provided during the early stages of the plant’s growth and red lighting during the later phases so that the plant gets just the perfect lighting conditions. When you put a grow light inside a grow tent, the effect amplifies thanks to it being a small enclosed structure and one which has reflective walls, which ensures that all the light bounces on to the plants. This is the reason why grow lights are critical for the growth of a marijuana plant and are highly beneficial. 

Different Types of Grow Lights

There are a number of different types of lights and you hear them in different terms and forms, etc. However, the primary three are – Fluorescent lights, High-Intensity Discharge grow lights, and LED grow lights. Let us look at all of them in detail 

1. What are Fluorescent Grow Lights?

In common usage, you might have heard of them as CFL grow lights or T5, T8 or even T12 grow lights.  When anyone talks of any of these types of lights, they are actually talking about a Fluorescent grow light. They are great for small growth setups. These lights are priced in pretty low and can fit into standard bulb sockets as well. You’ll need a CFL above 40W in order to grow cannabis indoors. You can get them in various color spectrums ranging from daylight to warm white to reddish white. However, the light output that comes from these grow lights is significantly lower compared to other types of grow lights and hence these need to be kept very close to the plants in order for them to absorb the light. 

2. What are High-Intensity Discharge (HID) Grow Lights?

HID Grow Lights are also quite popular among a certain old-school generation of growers who aren’t willing to switch to LED grow lights yet. You might not have heard of ‘HID’ lights per say, but you might have heard of High Pressure Sodium (HPS) grow lights and Metal Halides (MH). These are the two different kinds of HID grow lights, each offering a different spectrum of lighting. Metal Halide lights are basically on the cooler (blue) shade of the lighting spectrum and are used prominently during the vegetative phase of the plant’s growth cycle and as plants begin to mature, growers can then switch to HPS grow lights which are then used to help the plant during the flowering phase of its growth. You usually need special ballasts in order to set up these lights. 

HID lights tend to cost lesser than other lighting solutions and are also quite bright. They’ve been a time-tested solution and are easy to use too. However, these lights tend to generate a lot of heat and consume quite a bit of electricity too. They also need a special hood and ballast system in order to be set up properly. Lastly, these bulbs aren’t really long lasting and need to be replaced much frequently especially when compared to LED grow lights

3. What are LED Grow Lights and Why are they Considered the Best?

The latest and the most popular kind of lighting system at the moment when it comes to growing marijuana indoors is that of the LED grow lights. Growers who prefer to grow their weed indoors tend to use them because they consume a fraction of the electricity that is consumed by older types of grow lights – thereby saving huge costs on electricity bills. In another major reason as to why LED grow lights are considered the best, it is because these lights often have a ‘full spectrum’ variant where you don’t need to switch the lighting setup as the plant changes its phase of growth. You can simply flip a switch and that’s done! 

These grow lights can last for over 100,000 hours and are known to be some of the best performers in the industry. LED grow lights generate much lesser heat when you compare them with HID grow lights – which is another huge plus point for the growers. You don’t need to have any technical know-how and don’t even need separate ballasts to run LED lights because they function in a simple plug-and-play mechanism. Their energy efficiency remains their best point. The one drawback that you might face is that these lights are a little expensive when compared to other types of lighting options but given what you are getting in exchange, the light totally pays off for itself in the long run.


Lighting During Different Phases of a Plant’s Growth Cycle

During the early stages of a marijuana plant’s growth cycle, it is a very young unit and its parts are frail. You need to provide it a lot of light as it needs lighting in order to grow taller and stronger. Lighting period can be really long – almost up to 20 hours or even more than that. The light can be quite close to the plants but make sure it is not too close that it damages the plants. This has to be taken care of because the plant is really young and would need a lot of care at that time. In this early stage, the cool-blue spectrum of the light is needed.

As the plant enters the vegetative phase of rapid growth, you can provide a mix of blue and red lights both – but more blue than red. At this phase, you can move the grow light higher up and cover a larger area. In this phase of growth your plants need about 16 to 18 hours of light every day and about 8 to 6 hours of darkness. Following this phase, the plant begins to mature and you will notice that the sex organs begin to show up so you can identify the male and the female plants. After you’ve separated the male plants, you will need to provide about 14 hours of light to the plants for the rest of this phase which is the ‘pre-flowering’ phase.

The shift from pre-flowering to flowering happens when you reduce the photoperiod even more and begin providing warm red light to the plants for a reduced number of hours – about 10 to 12 hours of lighting and about 12 to 14 hours of darkness. This is how you need to provide lighting to your plants through the different phases of their growth cycle. 


Buyer’s Guide to Grow Lights: What to Consider Before You Buy a Grow Light

Now that you know which are the different types of grow lights and why grow lights are important for growing marijuana indoors, you must must also know about some features that must be kept in mind before you buy the grow light of your choice. These are the features on the basis of which you can compare between different grow lights and decide if the one you want to buy stands good on all of these parameters:

  • Power Draw – This is the most important thing. You must know how much power your grow light tends to draw. You must look for a grow light which draws the least power while giving you the maximum possible output. Don’t go by the ‘W’ Watts indicator that they show on the product’s name – that’s usually the output you get. The actual power draw is always in the product specifications which tells you how much power does. LED lights usually have the least power draw compared to the output you get.
  • CoverageThe coverage that the light offers matters a lot. You first need to set up your plants together and see how much area they occupy. Then you need to check the specifications of the grow light that you are planning to buy and see what is the coverage that the grow light is offering. The coverage in the flowering stage should be at least equal to, or slightly larger than your existing setup of plants. Make sure you use the flowering coverage to measure because that offers a more accurate picture.
  • Bulb QualityThe quality of LEDs or bulbs that are being used in the grow light matter a lot as well. Growers need to make sure that they are getting just the right kind of bulb which is a good-quality product and will last them for a long time. If you’re getting an LED grow light check which manufacturer has made the LEDs and if they’re made in America or made in China. Usually American-made LEDs tend to last longer compared to their Chinese counterparts. The better the bulb quality, the longer the lifespan of the grow light as well – LED lights generally tend to last for over 100,000 hours if made of the right quality
  • Dimmer- Check if your grow light comes with a dimmer. This is usually something that is a part of LED grow lights. Having a dimmer helps the growers reduce or increase the lighting based on the needs of the plants and ensures that the intensity can be increased or decreased based on the phase of growth the plant is at.
  • Brand CredibilityThe credibility of the brand also tends to matter a lot. You need to make sure that you are getting the grow lights from a good brand which will honor the warranty. Usually getting an LED grow light from Viparspectra, Vivosun, PlatinumLED, KingLED, etc. are considered to be a better option than going for unknown or lesser known brands.
  • SpectrumA full-spectrum grow light usually better than getting spectrum-specific grow lights because then you can simply flip a switch and get a better outcome rather than having to change the grow light every time your plant matures from the vegetattive to the flowering stage. Full-spectrum grow lights cover everything including the Ultraviolet and Infrared lighting needs of the plant. Just make sure your light has a high PAR value too.
  • DurabilityThe grow light that you are buying also needs to be durable enough to survive some accidental bumps and falls. Make sure its a sturdy and good quality grow light while also not being too heavy or bulky at the same time. Durability is important and many growers are worrying about it as lights are now growing thinner and sleeker with every passing day.
  • Daisy ChainingDaisy Chaining is a feature which helps the growers hook one light on to another instead of having to plug all of them individually to the power sockets. This is a double-edged sword, however. Make sure that you are buying good quality grow lights if you plan on daisy chaining because this can sometimes lead to power surges or overheating which might be a safety risk.
  • Cooling MechanismThe cooling mechanism in your grow lights needs to be top-notch. Especially if you are using something like a High Intensity Discharge grow light, or an LED grow light with a very high wattage – make sure there are sufficient heat vents and sinks and fans in your grow light which will dissipate all the heat and prevent it from accumulating inside the device. This can damage not only your grow light but also be a potential fire hazard. Keeping it cool is the reason why many LED grow lights even have holes in the front panels so that the light can ‘breathe’ and the hot air can move out.
  • Cost and WarrantyLast but definitely not the least of these points, cost and warranty matter a lot. Grow lights can cost anywhere between $60 to $600 a piece but make sure you’re setting a budget and make sure you know which your main grow light is, which your secondary lights are and which your backup lights are – and spend accordingly. Most grow lights offer two to three years of warranty, while others in the more premium category can offer upto 5 years of warranty, so check accordingly. 


Frequently Asked Questions about Grow Lights

Here are some of the most common and frequently asked questions about grow lights for growing marijuana indoors – many of you too, might be having similar queries so do take a look at these. 

1. Can I grow marijuana without using grow lights?

Yes, you can grow weed without using grow lights by keeping it either outdoors or near a window where it gets some sunlight. However, the results won’t be as good as using a grow light because grow lights give you the complete control to set up the optimal lighting as you can move it closer and farther, increase the lighting hours etc. Depending on natural light means there will be cloudy days or days with less light which isn’t really great for a healthy growth.

2. Are grow lights needed for outdoor growth also?

Not necessarily, but they can be combined along with using a greenhouse to get even better results. The greenhouse allows sunlight to enter and helps the plants grow and after sunset grow lights can be used to give an extra boost to the plants. However, you can also grow weed outdoors without using grow lights – but same as the above answer, it won’t really be ‘optimum’ growth.

3. How much do grow lights cost?

Depends on light to light, what features you’re getting, what wattage the light is and how much area it covers. Grow lights range from under $50 to over $600. They are available in all budgets.

4. Are grow lights legal?

Yes. Grow lights are legal to use as many growers also use them to grow fruits and vegetables or even ornamental plants indoors. However, if you are planning on growing weed using your grow light, the only thing you need to worry about is the legality of weed. If weed is legal in your area and if you are allowed to grow it and if you are growing in the right amount, there won’t really be a problem. Basically, using grow lights in itself will never be the cause of a legal problem.

5. What else do I need apart from grow lights to grow marijuana indoors?

Apart from grow lights, you also need grow tentsventilation kits (inline fans and carbon filters), and in some cases humidifiers/dehumidifiers, heaters and air coolers, etc. You’ll also need a steady supply of water and nutrients and these are just some of the most basic things.  



To conclude, we hope this article about grow lights for marijuana plants helps act as a complete primer to everything that you need to know about grow lights before you start growing your own weed indoors. Growing marijuana indoors might seem like a big challenge at first but when you get hands-on with it, it is actually a simple task which requires you to follow certain basic guidelines and then the plants grow by themselves! If there are any more questions that you have or if you feel there’s something that we’ve missed out on, do let us know in the comments below and we shall get back to you shortly!

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  • Rob Wilson

    Rob Wilson is a maverick horticulturist and alchemist of the herbal world. With an uncanny green thumb and a passion for unlocking the secrets of cannabis cultivation and processing, he blends science and artistry to orchestrate nature's most intricate symphony. Rob's journey is an odyssey of coaxing delicate trichomes and potent terpenes into harmonious existence. When not lost in his garden, he's a devoted educator, guiding fellow enthusiasts through the verdant realms of cannabis cultivation.

    https://mediafi.org/rob-wilson/ mediafi@gmail.com Wilson Rob