How Many Grow Lights Do Your Plants Need?

Posted on Jun 23 , 2020


We like to grow Cannabis because it’s the safest and best way when taking both legal and health risks into consideration. But at the same time, growing cannabis can be an expensive hobby. It’s often not the soil, fertilizers or seeds, hurting our wallets the most. It’s the annoying electricity bill we get every single month production is running. So in order to maximize the energy efficiency for your indoor cultivation, you need first to do some necessary measurements for what is optimal grow lights amount you need for your cultivation purpose.

How To Install Your LED Grow Light In The Right Way?

How many buds do you want to harvest?

Let’s say a potential grower wants to consume about 30g of bud every month. Just one single autoflowering plant is easily capable of producing this amount of bud in an 8 weeks life cycle. This means a potential harvest of 120g after two months when growing just four small autoflowering plants. This is enough to last for about 4 months in this particular case. This hypothetical weed farmer could grow 2 months, take a break for 2 months, and then continue to grow again.

What has to be taken into consideration is that autoflowering varieties need a light cycle of 18/6, 20/4, or 24/0. This of course lowers their overall energy efficiency because “regular”, or “feminized” cannabis strains, only need 12 hours of artificial light when grown indoors. 

The point is, to perfectly match the amount of energy, you put into your plants, with the amount of bud you need for your private purposes.


Measure the Area(sq.ft.) of Your Canopy


When you have decided how many buds do you want, then you can decide how many plants you need to grow. You can simply consult the seeds or cuttings seller to get an approximate output per plant of specific strains. How many plants lead to how big the area you need to place them. Calculating your lights depends entirely on the size of the Canopy. The canopy is the area of your grow room that your plants occupy. This is the only area of your grow room or grow tent your grow lights should be focused on (the old method calculates for the entire room, which wastes lots of light). To do this, simply measure the length and the width of the area you’re going to have your plants in, and multiply them together.

Find the right LED GROW LIGHTS

The common lighting technologies are kind of problematic when looking at them from an efficiency point of view. These lamps have really high wattage between 250-1000W. This is not a problem at all. The amount of buds always correlates with the amount of energy you put into the “growing-equation”. But it depends a lot on how good the ratio between yield and energy is.

The gram: watt ratio is something to start with. This ratio is not really ideal because it doesn’t necessarily consider the total amount of light hours being used. Longer flowering periods lead to a higher number of light hours you need to produce the desired quality.

Please note, the ratio also varies considerably for different strains, for example, under the same best quality LED grow lights, blue dreams can yield as much as 1.5 g/watt, while UK cheese gets only about 1 g/watt.

The thing about these high pressure sodium lamps is that energy, you personally have paid for, gets converted into heat, which then has to be extracted, by using more energy you have to pay for. The heat can be quiet beneficial if you live in a colder region like Alaska, but oftentimes it’s a bigger concern to get temperatures down, than up.

New technology like LED lights though, can be a good option to lower your energy costs by still producing top-shelf buds.

LEDs emit lower heat and oftentimes have a light spectrum that is specifically tailored to plants’ needs. This means higher efficiency because less power is converted into heat, and into a light spectrum, the plant doesn’t fully appreciate it.

The most reliable way to figure out how much light you need to light your canopy is by using the “Watts per Square Ft.” method. This method says that you should give your canopy 40 to 50 watts per sq. ft., when you use LED grow lights.

Optimize the Air Environment

Most experienced growers will agree that it’s generally better to oversize the air system of an individual grow room, or tent. The reason for this is the following: Let’s say you have the feeling that your cannabis plants perform best when they are being grown at a temperature of 26 °C. Your lamp emits a good amount of heat and it’s hot outside, maybe 30 °C. Your air system runs on full power to get the temperatures down. What happens if it’s 16 °C outside? Does your air system still need to run on full power? Most likely not! This is when you can turn it down and save energy.

Installing an electric transformer that is able to reduce the voltage for your extracting tube vent is a smart move. If you have installed a transformer like this, you simply let your vent run on different velocities to safe energy when conditions allow this.

You can use a simple 5-level electric transformer that is normally used to regulate ceiling fans, they cost you a few bucks and are the cheaper alternative to the expensive ones from the grow shop. Beware of cheap “speed-controllers” or “dimmers” for your extracting tube vent, they tend to produce this annoying dimming-noise and are not suitable for any kind of silent grow operations.

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