What Power LED Grow Light Should We Choose?

This is something many people wonder about when they start using LED grow lights.
There is a mix of too much technical jargon and marketing hype, making it confusing to choose the right LED grow light.

A good rule of thumb for optimal yield is to choose an LED grow light that outputs at least 50 watts per square foot of growing space. This can serve as an important reference.

The most important equipment in a grow room is the light. Why? Light is food for plants. You need to provide high-quality food for your plants so they can produce high-quality yields. Due to their energy efficiency, durability, and full spectrum, LED grow lights are now considered the best lighting choice by most growers.

However, even knowing how to choose an LED grow light and understanding the related technical terms, finding the right light for your growing project can still feel a bit overwhelming.

To determine what size LED grow light you need, you first need to calculate the exact dimensions of your growing space.

Size of the Growing Space

When cultivating plants, a good rule of thumb is to use at least 50 watts of LED grow light per square foot of growing space.We want to flood our plants with light (food) so they have enough energy to produce robust, substantial buds.

Therefore, we need to calculate the square footage of the growing space (length x width).Then, we multiply this number by 50 watts to get a rough estimate of the required grow light wattage.

Example: I have a growing space that is 2 feet long and 3 feet wide. This gives me 6 (2ft x 3ft) square feet of growing space. I then multiply this number by 50 watts, resulting in 300 watts. So, in this example, I would need an LED grow light of at least 300 watts.

Generally, each cannabis plant cultivated requires at least 1 square foot of growing space.

After germination, many growers prefer to place one plant in a large 5-gallon grow bag, which is about 1 square foot in diameter. The plant then remains in this pot until it flowers.

This allows the plant to grow large and strong without being hindered by other plants or the sides of the tent. It also avoids frequently transplanting the plant, which can cause significant stress.

Now, it's also important to understand that most LED grow lights typically only cover about 1 to 6 plants.
If you plan to grow more, you will need to purchase multiple lights and hang them side-by-side to ensure each plant receives the same amount of light.

The table below illustrates how the wattage you need increases with the size of your growing space, and also includes how many plants are suitable for each size of grow light.

*Note: 1 square foot of growing space = 50 watts of LED grow light*

Growing Space	Minimum LED Grow Light Power Requirement	Number of Plants That Can Be Cultivated
2 sq ft (2×1)	100w	1-2 plants
4 sq ft (2×2)	200w	1-3 plants
6 sq ft (2×3)	300w	1-6 plants
9 sq ft (3×3)	450w	1-9 plants
12 sq ft (3×4)	600w	1-12 plants
16 sq ft (4×4)	800w	1-16 plants
20 sq ft (4×5)	1000w	1-20 plants

In these cases, the size of the growing space will require you to purchase multiple grow lights hung side-by-side to ensure the entire canopy receives light.

Note: The values above are for reference during the flowering stage. During the seedling and vegetative stages, you may need to reduce the power accordingly.

Simply put, PAR is a measure of the part of the light spectrum that plants use for photosynthesis, so it's an important factor. The higher the PAR output of a grow light, the more light the plants receive:

Growth Stage	Optimal PAR Output (or PPFD)
Seedling	200-400 (μmol/m²/s)
Vegetative	400-600 (μmol/m²/s)
Flowering	600-900 (μmol/m²/s)

 

Ideally, you should choose an LED grow light that outputs PAR within the ranges mentioned above.

This almost rules out LED grow lights below 300 watts, as they simply don't have enough power to produce the required PAR levels. These are the optimal PAR levels. Using a grow light with PAR output below these ranges won't cause serious harm, but it won't maximize the plant's growth potential.

We hope this article clarifies how to choose the right size grow light to supplement light for your project. As long as you know the size of your growing space and how many watts are needed per square foot, choosing an LED grow light is quite straightforward.