What Kind Of Light Do You Need To Grow Weed

Growing weed indoors can be fun, but they require a lot of commitment and dedication. They come with their own set of advantages and disadvantages. While not all plant species are good for indoor cultivation, there are some specific strains that are suitable for their wide and short growth. If you are starting out, there will be many things that you will need to consider such as the home grow space, light, cooling systems to prevent burning and so on.

If you want a nice and healthy weed, you need to use the right type of light. The one thing that the weeds need to grow properly is light as this is the main food required for photosynthesis. As a beginner, you will worry about what kind of light do you need to grow weed.

The weed plant basically has two growth stages and they are the vegetative stage and the flowering stage. Before we tell you which light is most suitable, let take a sneak peek into these two important stages.

The Vegetative Stage

When the seed is planted, the first stage is the vegetative stage. In this phase, the stems slowly start to grow and it gets ready for the flowering stage. This stage may last for about one week or as long as 40 days. For the most effective results, it requires a day light cycle of 18 hours on and 6 hours off. Some growers may choose to provide a 24 hour light cycle to stimulate a faster growth.

The Flowering Stage

As the weed transitions from the vegetative stage to flowering stage, the need for light also changes. The growers need to identify this shift and switch the day light cycle to 12 hours on and 12 hours off during the flowering stage. This phase starts as soon as you switch the light cycle which stimulate budding. This period may start after 40 days or a few weeks. As a grower, you need to use your own instinct to decide when to end the vegetative stage and stimulate the flowering process.

If you are a new grower then bear in mind that not all weed strains are alike hence their growing techniques will also vary widely. The different types of growing techniques will produce different kind of results. While some strains may mature faster and get ready to enter the flowering stage, there are some that take a little longer.

What Kind of Light do You Need?

So, now coming back to the main question – hat kind of light you need to grow weed in the flowering and vegetative stage.

For the vegetative stage, the best type of light you can use is the fluorescent bulb as weeds love blue light in the spectrum. The fluorescent bulbs are most common type of light used by home growers for the vegetative stage. Efficient energy and low height output are the two main benefits that make fluorescents a good option.

There are basically two types of fluorescent bulbs that you can use to grow weed and they are compact fluorescent bulbs (CFLs) and T5 lamps. While CFLs are a low cost solution, the biggest downside is that the light is not concentrated as it spreads across a wide area.

While it would be unfair to expect large and dense buds using CFLs, that shouldn’t mean you cannot use them. Some people manage to get a decent harvest with just CFL bulbs. So, use your creativity and make sure you dedicate good amount of time for this to see great results.

If budget is not a constraint, we would recommend that you choose a T5 lighting system. They are the advanced version of high output fluorescent lights. They are capable of emitting more dense and intense light than any other standard fluorescent bulb. The only downside is the cost factor as the T5 lights may cost you more than any HID system.

When using fluorescent lights, you can hang them as close as you can to the plants because they don’t produce a lot of heat. We would recommend that you use 6500K bulbs for the vegetative stage and 2700K for the flowering stage.  Even when you are using a T5 lighting system, you may include some CFLs wherever there is space.

High Intensity Discharge (HIDs)

The HIDs are another good source of light that can be used to grow marijuana. There are basically two types of HIDs – Metal Halide (MH) and High Pressure Sodium (HPS). We would not recommend using Metal Halides unless you have the license to grow medical weed or it is legal in your state. The high energy bills will attract the attention from authorities so it is always better to be on the safe side. The HPS are a better option as the light is only needed 12 hours a day so that means less energy consumption.

If you are thinking of installing any of the above mentioned HIDs to grow weed, you may need to consider a few things before investing in this type of set-up. The most important of all is heat management. As these lights produce a lot of heat, it is essential that you choose some kind of ventilation. Get a good quality centrifugal fan to save yourself from the frustration and get a decent harvest.

When choosing HID light bulbs, you will get three different types of lights – 400W, 600W, and 1000W. Choose the intensity of light depending on the amount of growing space you have available.


Let’s summarize what kind of light you need to grow weed. Never use incandescent lights as they have practically no use in your indoor garden.  Fluorescents are a great option for the beginners and if you can stretch your budget a little more, get a T5 light system. Choose an HID system, only if you and the growing space can handle that intensity. Whatever you choose, stay safe over anything else. Stay protected and prevent fire or other health hazards.

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James Alexander James Alexander
Hey, I'm James! The founder and head writer here at GreenBudGuru.com. I started this site to share my passion and knowledge of all things cannabis. I used to work as a budtender in central Amsterdam, and have over 7 years of growing experience.

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