Grow Lights: How Many Watts Per Plant/Square Foot is Needed?

One consideration in setting up an indoor grow space, such as a grow tent, is the number of lights you need, and with LED Grow Lights as the way to go in indoor growing, it’s essential to know the capacity of an LED fixture for you to maximize its potential.

With LEDs being more efficient than the traditional HPS, you can’t use the same rules in setting up an indoor space using the former, as this can damage your plants. That said, how many watts per plant do you need for LED Grow Lights?

And the answer: it depends.



Factors That Affect LED Choice

There are two factors that you need to consider when choosing the wattage of the LED Grow Lights.The first would be the plant you’re growing, and the second would be the total area of your grow space.


Type of Plant

Plants have different lighting needs, which is why you need to know how much light a plant needs. As a rule of thumb, the higher the wattage, the more intense the light is. Leafy plants and herbs usually need lower wattages. Fruit and flowering plants like tomatoes and cannabis need higher wattages. The amount of power you need for leafy plants would often be half of what a flower-bearing plant needs.



Total Area of Grow


Indoor Grow Area


When it comes to the total grow space area, this pertains to how much space your plants cover and not the footprint of your space. That will help you also decide how much wattage you need for every plant.

Different growing techniques are a consideration in the total area of growth. And while that affects wattage, you can’t just split the light to get the right amount of power. Instead, you can use that light in a position that can help benefit multiple plants.

So, how much do you need per plant per area?

Thirty-two watts of power should be enough for every square foot as a rule of thumb. You can go a bit low to 30, but don’t go beyond 40 per square foot. So how good is a 32-watt LED?

Let’s take the Screen of Green technique as an example. A Screen of Green needs about 0.25 square feet of grow space. With a 32-watt LED grow light, you can provide enough lighting for four plants. For a Sea of Green, the same 32-watt grow light can provide lighting for one plant.

On the other hand, 32-watts of power won’t be enough for a low-stress training, which occupies at least two square feet of grow space.

As you can see, you can use a grow light for multiple plants. But take note that it’s not ideal to do so all the time. For one, the lighting coverage on the outer part of the light’s footprint isn’t as beneficial as being close to the center. And while you can cram plants under a grow light, the results won’t be as helpful.

Sounds simple? There are some considerations to consider with the grow space and wattage.



Photosynthetically Active Radiation (PAR)


Image courtesy of


PAR, or photosynthetically active radiation, is just as important to know when deciding how much lighting you need to grow your plants. PAR measures the intensity you need to grow your plants. To give you an idea, leafy plants need around a PAR of 200, while fruit-bearing plants would thrive between 400 – 500, depending on the plant.

Knowing how much PAR a grow light has will affect how a plant grows. If the PAR is too low, your plant will have a hard time growing and will likely have stunted growth. Too intense lights, meanwhile, can burn your plants. That’s why LED grow lights need to be set at an optimal height, even with the lower heat emission.



Wrapping Up

Setting up LED grow lights in your indoor space need not be complicated. As long as you know the capacity of your grow lights, you can maximize the potential of your fixture, as well as your plants. With the proper settings, your plants can thrive to their fullest while operating at lower costs.