September 8, 2014

How Many LED Watts Are Required Per Square Foot of Grow Space?

The Ultimate Guide to Help You Choose the Correct LED Wattage for Your Grow Space (during flowering)

Are you new to the world of LED growing? If so, the charts below will help you determine how much energy (by wattage) your plants require for flowering.

Disclaimer: Wattage is a relic of the HID (MH and HPS) days. Wattage should not be used to determine the coverage area a fixture or the usefulness of an LED grow light. Wattage should only be used as a simple method for approximating the correct fixture size for your grow.

PPFD (umol/j/m2) and DLI is the correct metric for measuring useful light intensity over a given area. Coupled with the correct spectrum for your plant type and phase of growth, PPFD (and spectrum) are the keys to a successful grow. However, for the purpose of estimation, we will report wattage calculations in this article.

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Grow variables

It is important to understand that the number of actual watts that you need for your grow will vary depending on:

Plant type (high light or low light)

High light plants - i.e. tomatoes, peppers, etc
Low light plants - i.e. herbs and leafy greens (such as basil lettuce)

Growth phase

Seedlings, vegetative, and flowering plants all require a different amount of light

Total area of your grow

A larger grow area will require more power

Watts per square foot

The average LED grow light draws about 40 watts to cover 1 sq ft for flowering. HID lights draw about 62.5 watts per sq ft. The energy saving that growers can expect from using LED grow lights instead of HID is around 38%. This energy savings only takes into account to savings growers gain when using LEDs fixtures. It does not account for other environmental factors where growers can save energy. For example, less ventilation and air conditioning may be used, or foregone completely, depending on the size of the setup and ambient temperatures. Total power savings may rise above 50% in certain scenarios.)

Different LED grow lights will have different efficiencies. More efficient LED grow lights will use fewer watts to emit the same amount of light that a less efficient LED grow light will emit. Therefore, wattage is not the most accurate tool to know how powerful of a grow light you need for a particular coverage area.

LED Wattage Chart Explanation

The wattages listed below assume you are flowering your plants. If vegging, you might consider reducing your wattage by 50% since vegging plants only require about half the light intensity. As always, it is best practice to follow the manufacturer's recommendations.

Using the charts

In each chart you will find the following columns:

'# of Plants' to be grown
Square footage that the respective number of plants cover
Recommended LED wattage for the number of plants grown in the respective space

Wattage charts

Assume about 32 watts/sq ft (actual LED wattage) for flowering. Fewer watts might equate to smaller yields while more wattage may lead to larger yields.

Quick Guide (watts per coverage area)

1' x 1': 40 watts

2' x 2': 160 watts

2' x 4': 320 watts

3' x 3': 360 watts

4' x 4': 640 watts

5' x 5': 1000 watts

4' x 8': 1280 watts

6' x 6': 1440 watts

Recommended wattage assuming 1.0 sq ft/plant

# of Plants	Square Feet	Wattage from Wall
1	1	40 watts
2	2	80 watts
4	4	160 watts
6	6	240 watts
8	8	320 watts
10	10	400 watts

Recommended wattage assuming 2.0 sq ft/plant

# of Plants	Square Feet	Wattage from Wall
1	2	80 watts
2	4	160 watts
4	8	320 watts
6	12	480 watts
8	16	640 watts
10	20	800 watts

Recommended assuming 4.0 sq ft/plant

# of Plants	Square Feet	Wattage from Wall
1	4	160 watts
2	8	320 watts
4	16	640 watts
6	24	960 watts
8	32	1280 watts
10	40	1600 watts

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Related: Best LED Grow Lights 2022

Notes: Please be aware that the cultivation of certain plants may or may not be legal within your own specific region or country. LED Grow Lights Depot does not encourage or condone any illegal activity and advises each individual / user to inform themselves of the relevant laws within their own region/country.

Previous article Best LED Grow Lights 2022 Video

Comments

Tarey - October 6, 2016
Seedlings do better with T8 lights. I grow mine in red cups until the root is really filling the cup. The T8 grows many more internodes than LED which gets your plant off to a great start. I clone first in a clone bucket – super great. Then when I transplant from the red cups, it’s into a gallon and 1/3 sized container. Same thing with the roots, let them grow into the container. When they are 1’ to 18" I transplant one last time into a 3-5 gallon container. I let them get comfortable and start to grow again. Then I set to flower. I’ve got 2 6 × 6 tents and I have about 1200 LED watts worth of UFO lights in each. Not much heat and I can lower and raise according to need. In one tent, instead of UFOs I have a Mars Hydro 144 in the middle – that’s 300 LED watts, though covering a larger area. LED is the best way to grow and flower, the taste, smell of your herbs are amazingly better. Starting with T8 there are many more internodes, i.e. places for flowers later. Or for cutting clones off. Don’t overpay for LED lights, because prices should be coming down not going up on these. A 300 watt light shouldn’t cost $1000! Shop around. Most ufo light dealers on ebay are great, I’ve bought from a few. They list the number of LED lights, the color and what it is good for. They can give great yields of top shelf herbs which is what you want. Some with UV etc even help chase away the evil mites. Good luck.

Zane - October 1, 2016
Whats a good estimate on amount of plants to put under 1000w full spectrum led 15 inches wide light

lindsay Branscombe - August 15, 2016
My question is the same as Kevin’s. Why are you using watts to talk about LEDs. Doing this chart (which could be SUPER helpful) with watts instead of lumens leaves the question of whether or not you’re talking about the actual wattage required to run the bulb or the “watt equivalent” of a typical bulb. ie: are you talking about an LED that requires 50 watts of power? Or are you saying an LED that produces the same amount of lumens as a typical 50watt bulb?

sheetal borkar - July 18, 2016
The LED grow light market is expected to rise to more than $1.9 Billion by 2020, growing at a Compound Annual Growth Rate (CAGR) of 26.93% between 2015 and 2020.

http://www.marketsandmarkets.com/pdfdownload.asp?id=237907331

kevin - July 3, 2016
why are you talking about wattage? plants use lumens. So, If have a system that can create more lumens with less energy input (wattage) that is the goal. which LED lights can achieve with computer chips. lumens = photosynthesis. watts are the input of energy to run the equipment that produces lumens. So question I ask is How many lumens do I need per square foot? The sun right is probably suppling well over 12000 lumens ?

Macy not putting - May 20, 2016
macynoelle2013@gmail.com

Macy not putting. - May 20, 2016
i understand that your suppose to keep the walls as close to your plants (or in other words keep them in an area that makes sense as to how many plants you have.) but in my case i have bought a larger grow tent than i needed but i wanted room for if i ever decided to grow more. but anyways im only growing about 6 plants and i have a 16 foot area how many watts would you say i need? i am have extreme trouble with this please email me!!!!!!!!!!

michael frazier - April 3, 2016
the black dog is a far more superior Led with its range and full spectrum. with veg range Phytomax 600 veg range 6×6 flower range 4×4

Koki - February 2, 2016
smd leds are not suitable for growing, un need to look for power leds.
in addiction, led bulbs emit light on a very specific frequency, one kind of blue and one kind of red are not enough. you need at least 440nm and 480nm on the blue and 640nm and 680nm on the red

Marsha Seitz - January 14, 2016
I have a tower garden which did great outside this past summer. Around the garden I put 4 4 foot strips of 9 blue 27 red 5watt each. Description says 15w 36 smd 5050. Is this enough to grow my plants. They aren’t doing so well.