How to choose the size of LED grow light?

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

The most crucial equipment in a growing greenhouse is the lighting. Why? Because light is the food for plants, and you need to provide them with high-quality food to ensure they produce high-quality yields. LED grow lights are now considered the best lighting choice by most growers due to their energy efficiency, durability, and full spectrum capabilities.

However, even with knowledge of choosing LED plant lights and related technical terms, finding the right grow light for your cultivation project can still be overwhelming. To determine the required size of an LED plant grow light, you first need to calculate the exact dimensions of your growing space.

When growing cannabis, a good rule of thumb is to use at least 50 watts of LED plant light per square foot of growing space. We want to flood our plants with light so that they have sufficient energy to grow. Therefore, we need to calculate the square footage of the growing space (length x width). Then, multiply this number by 50 watts to get a rough estimate of the wattage of the plant light needed.

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

How many plants can be grown?

Generally, each cannabis plant requires at least 1 square foot of growing space. After germination, many growers prefer to place one plant in a large 5-gallon planting bag with a diameter of about 1 square foot, and the cannabis plant remains in this pot until flowering. This allows the plant to grow large and robust without being hindered by other plants or the sides of the tent. This avoids the need for frequent plant transfers, which can cause significant stress to the plants.

Ensuring coverage of your canopy:

It is also important to understand that most LED plant grow lights typically cover only around 1-6 plants. If you have plans to grow more, you will need to purchase multiple lights hung side by side to ensure each plant receives the same level of illumination.

The table below illustrates how the required wattage increases with the size of your growing space and also includes the number of plants suitable for each size of plant grow light.

2 sq ft(2×1) 100w 1–2plants
4 sq ft(2×2) 200w 1–3plants
6 sq ft(2×3)300w 1–6plants
9 sq ft(3×3) 450w 1–9plants
12 sq ft(3×4) 600w 1–12plants
16 sq ft(4×4) 800w 1–16plants
20 sq ft(4×5) 1000w 1–20plants

Note: For these scenarios, the size of the growing space will require you to purchase multiple plant lights hung side by side to ensure the entire canopy receives adequate lighting.

Understanding PAR Output:

PAR, in simple terms, is part of the spectrum parameters that measure the light spectrum used by plants for photosynthesis, making it an important consideration. The higher the PAR output of a plant light, the more light the plants receive.

The table below provides the ideal PAR range for each stage of the cannabis growth cycle as a reference:

SEEDLING 200–400umol/m2/s (PAR or PPFD)
VEG 400–600umol/m2/s (PAR or PPFD)
FLOWERING 600–900umol/m2/s (PAR or PPFD)

Ideally, you should choose an LED plant grow light that outputs PAR within the ranges mentioned above. This virtually rules out LED grow lights below 300 watts as they simply do not have enough power to produce the required PAR levels. These are the optimal PAR levels, and using grow lights with PAR outputs lower than these ranges will not have any severe consequences but may not maximize the plant’s growth potential.

We hope this article clarifies how to choose the right size of plant lights to supplement your project. As long as you know the size of the growing space and the wattage required per square foot, selecting LED grow lights becomes straightforward.

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HIBOCT C-1000W : https://hiboctgrow.com/c1000/
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HIBOCT C-900W UVIR: https://hiboctgrow.com/c900uvir/
HIBOCT C-1000W MAX 1.8M: https://hiboctgrow.com/c1000max/

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