How Many Grow Lights Do Your Plants Need?


In order to properly answer the question "How many grow lights do your plants need?” you will first need to examine a few key factors. 

You need to consider the exact grow space you are working with, the type of lights you have, and the growing technique you are going to be using.  You will also want to consider the type of plants you are growing. 

Will they be large and tall or short and bushy? 

All of these questions must be answered properly in order for you to narrow your lighting needs down to the exact amount. 

Here a few tips to get your lighting scenario on point.



The Type of Lights You Use Matters

If it is at all possible, you should use a LED lighting system.  LED lights are more compact so they can be mounted without placing a large height restriction on your plants. 

They run much cooler than tradition high-intensity lighting systems so you can have more lights in a smaller area.  High-end LED lighting systems also feature a full lighting spectrum.

 This can give your plants more usable light and access to the much needed ultraviolet and infrared lighting spectrum.  All of which helps to increase your plant's productivity.

This can give your plants more usable light and access to the much needed ultraviolet and infrared lighting spectrum.  All of which helps to increase your plants productivity.


Measure Your Canopy

To determine the square footage of your garden simply measure the width and length of your gardens canopy.  Remember it is your canopy that requires light, any other parts of your garden need not be accounted for when doing your lighting calculations.


Watts per Square Foot

In a traditional garden running a high intensity lighting setup, you are going to want approximately 65 watts per square foot.  For example, if you have a 60 sq. ft garden you would use this equation to calculate the amount of HID lighting you will require to produce maximum yields.


  • 60 sq. ft. x 65 watts = 3900 watts


If you are utilizing a LED lighting system, you can reduce the amount of watts per square foot by more than half.  With a LED lighting system in place, you will only require 32 watts per square foot, so the exact same garden with a LED set up would use this equation.


  • 60 sq. ft. x 32 watts = 1920 watts


Spacing Is Important

Your lights are going to have a sweet spot or a spot where the maximum amount of PARS are located.  This is going to be the optimal location to place your plants, as they will get the most usable light in this area.  No matter what type of lighting system you use, directly below your light is going to be the most effective PAR location.  To avoid uneven growth you should space your lights at a distance to where they are getting some sort of overlapping occurring.  You should also rotate your plants or the position of your lighting to allow for a more even distribution of your plant's nutrients.  Never press your plants tight against each other.  Cannabis can sense when it is touching another plant and if it does, it will restrict its growth to prevent competing for light.



All of this means one important thing.  Adding more plants to your garden does not necessarily mean you will get more yield and at a certain point, adding more plants to your garden will actually reduce your productivity.  The key is to get the optimal balance needed to allow your plants to prosper under your lighting.



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  • David Hamilton
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