How Many Grow Lights Do You Need?


grow light
Before purchasing grow lights, it’s crucial to choose the right size and quantity for your garden to save time, energy, and money. Start by considering how many plants you want to grow and the space available. If you’re a hobby grower, be aware that your state may have legal limits on the number of plants you can cultivate. With a clear plan, we can help you determine the number of grow lights you’ll need.

Calculate your grow light wattage requirements – how many grow lights do you need

How many watts per square foot?

We need to estimate the coverage of grow lights by wattage. Although this can be affected by many factors, such as the efficiency of the grow lights. But it’s still very useful, especially if you’re growing in a grow tent or another small area.

Typically, Vegetative growth requires 20 watts per square foot and Flowering growth requires 30 watts per square foot.

Measuring plant canopy

Now we know that the wattage required for plant growth is an average of 20-30 watts per square foot. Please note that you should measure the area occupied by the canopy of the plants you are growing rather than the area of the tent itself. If you’re growing in a 4×4 tent but your plant canopy is only 3×3, you don’t need a grow light that can illuminate a 4×4 area.

In addition to the size of the plants at maturity, we also need to consider the height of the plants, as well as the spacing between plants, these all need to be calculated.

light coverageLight Coverage| vs2000 grow light

Most lights are measured in watts and lumens, but PAR (Photosynthetically Active Radiation) is a factor that must be considered when purchasing grow lights. “PAR” means the light that plants can use for photosynthesis.

PAR looks typically at the wavelength range of 400nm to 700nm, the visible light spectrum. PAR is measured by PPFD, and its value represents how much PAR is generated in a specific area in one second.

When you look for LED grow lights, most brands will describe their PAR—you can choose the best LED grow light according to your needs.

How many watts do I need?

The table below is our recommended wattage for different sizes of grow rooms.


Grow Room Size


Square Feet


Veg Wattage


Flower Wattage

2’ x 2’ 4 80 watts 120 watts
3’ x 3’ 9 180 watts 270 watts
2’ x 4’ 8 160 watts 240 watts
4’ x 4’ 16 320 watts 480 watts
5’ x 5’ 25 500 watts 750 watts
4’ x 8’ 32 640 watts 960 watts
8’ x 8’ 64 1,280 watts 1,920 watts
10’ x 10’ 100 2,000 watts 3,000 watts

Now that we have an idea of the approximate wattage of plant lights required, you can determine the number you need based on your actual situation.

For example, if you decide to grow inside a 4×4 grow tent, then you’ll need to grow lights of around 480 watts. You can choose 1 grow light with 480 watts or use several grow lights that add up to 480 watts. If you’re growing using clone, ScrOG, or SOG, methods, then I suggest you use several lights of different wattages.

For grow lights, the further you get from directly beneath the light, the weaker the light becomes. In these situations, one light probably won’t be enough to cover the crowded space. If you only want to grow 1-2 large plants, then one grow light with enough wattage will suffice and it will be more convenient to set up but if you plan to grow a ton of plants with a lot of canopy, you should try to overlap light coverage so all of your plants are getting max light. You might also want to rotate your plants around your tent throughout the grow.

Wrap-Up – How Many Grow Lights Do You Need

Every grower has an extraordinary passion for grow lights because they pretty much determine what a plant can grow into. They can be expensive and the biggest expense sometimes comes during growth. 

More Information about Light Distance and Light Intensity:

How Far Away Should My Grow Lights Be?

How Far should Seedlings be from Grow Light ?

What’s the Best Grow Light? Unveiling the AeroLight Revolution by VIVOSUN

What You Need to Know About Grow Lights?

Why Should You Choose the VIVOSUN LED Grow Light?

If you have any questions, please don’t hesitate to reach out to us!

And be sure to check out our other blog posts for useful tips on becoming a great grower!

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