How Many Watts Per Square Foot For LED Grow Lights?

Indoor gardening has gained lots of grounds in recent years. A few decades ago this idea was only read on books with less practicality in real life. Light being a basic need for plants to grow it is essential to have adequate light in a grow room for maximum yields. LED grow lights are undeniably the best artificial lights however, how do you determine how many watts per square foot for LED grow lights?

What is wattage?

A wattage is a unit used to measure the amount of power/ energy consumed on lighting a bulb. Most people mistake wattage for brightness. Wattage doesn’t measure brightness but there is a positive correlation between the number of watts and the brightness of the bulb measured in lumens.

Understanding PAR output

PAR output

For maximum plant yields, the artificial light should provide different light spectrums similar to that of the sun. As much as you should know how many watts per square foot for LED grow lights, understanding the concept of PAR output is essential if you are to provide your indoor plants optimal light.

What is PAR? 

The initials PAR stands for (Photosynthesis Active Ratio) and this is the part of the light spectrum used by plants for photosynthesis. From basic third grade science, the essence of light in plants is to carry out photosynthesis. This being the process in which plants make their own food you can now understand essential light is to plants.

There are different light spectrums but only a portion of it is used to carry out photosynthesis. Different artificial lights vary when it comes to PAR but LED grow lights have the highest PAR with is the plant edible part of the light.

The following is a table showing the requirement for the PAR Output in different growth stages

Stage of Growth

PAR Output







How Many Watts Per Square Foot for LED Grow Lights?

There are lots of factors that determine how many watts per square foot LED lights that are needed. These variables are:

1. Type of Plants

Different plants vary when it comes to lighting needs. Some plants require more light whereas others require average light. In particular, plants with a canopy require more light so that it would penetrate beneath and, more light means more watts.

Examples of high light intensity plants include tomatoes, pepper, and cannabis. Herbs, on the other hand, require average lighting.

Before you can decide on the required wattage it is essential that you first determine the lighting requirement of the plants you are to grow. Inadequate and too much light both affect the output of plants negatively, therefore, you should hit the balance.

2. Growth Phase

Basically, plants have three growth phases germination, vegetative and flowering. In the three phases, the lighting requirements are different explaining why some of the best LED lights have an adjustment button for the various phases.

During germination, plants require less light, this increases when the plants reach the vegetative phase. Flowering is the prime high light requirement for plats. High light intensity is essential for plants to flower and produces big buds.

3. Number of Plants

As much as you want to grow more plants in the grow tent one thing should be certain. Plants need breathing space and hence should be adequately spaced depending on the type of plants.

The number of plants in the growing area is also a variable essential that should never be ignored when determining the number of watts needed per square foot. The more the number of plants the higher the wattage requirement and vice versa!

4. Spectrum light

The sun has light spectrums but unfortunately, they cannot be seen with a naked eye. LED grow light full spectrum is, however, visible to the eye. In particular the red and blue spectrums are highly recommended since they are known to support flowering and vegetative.

5. Light Reflectors

The idea of light reflectors is new to most people but this doesn’t mean that it isn’t necessary. For optimal light usage reflectors are essential. When done right, reflectors can reduce the wattage per square foot needed to maximize plant yield.

What is the essence of reflectors in a grow tent? Reflectors are essential in the sense that they reflect and concentrate light on the plants.

This is particularly useful given the fact that; walls of most grow rooms are dark and the last thing you want is walls that absorb light meant for the plants.

Calculating Wattage Requirement Per Square Foot for LED Grow Lights

Among all artificial lights, LED grow lights have the highest PAR and have more lifespan. An average LED light runs for 10,000 hrs. To extend the lifespan some companies set the lights such that full capacity is not used.

Some lights will be written 5 watts yet only operate on 3 watts. This, however, should not be an issue in calculating how many watts per square foot of LED grow lights since we shall highlight the average requirement per square foot.

On average for a 10 square foot grow area 400 watts is sufficient. The average wattage requirement per foot for LED grow lights is 40-50watts. This is however not standard since different LED grow lights vary some are energy efficient and will use fewer watts for the same kind of lighting. 40-50 watts is just the average standard.

The size of the LED grow light also matters if big this means that it will cover a relatively large area. A smaller grow light bulb will mean that only a small portion will be covered and hence more watts will be needed to illuminate a large area.

Quick table showing the usual wattage per coverage area

Grow Tent Size


1' x 1'

30W - 42W

2' x 1'

60W - 90W

2' x 2'

120W - 150W

2' x 3'

200W - 220W

3' x 3'

25W - 300W

3' x 4'

380W - 400W

4' x 4'

500W - 600W

4' x 5'

600W - 650W

5' x 5'

750W - 800W

5' x 6'

900W - 1000W

6' x 6'

1100W - 1200W

6' x 7'

1200W - 1500W


It is one thing deciding on the best LED grow lights and another determining how many watts per square foot. This post has walked through everything you need to know about wattage requirements. There is nothing holding you back now.

1 thought on “How Many Watts Per Square Foot For LED Grow Lights?”

  1. Plants and especially cannabis need most lighting during the flowering stage, so we`ll be using that as an estimate of how much area needs to be covered. A standard LED grow light must use more than 32 watts per square foot of grow space, but for optimum results it should be over 50 watts, up to 80 watts.   Consult with the following bullet points if you need a quick guide for calculating how many watts you need for a given grow area.


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