What Size LED Grow Light Do I Need?

what size led grow light do I need?

The most important bit of equipment in your grow room is your light.

Why? Light is your plants food, you need to feed your plants high quality food for them to produce high quality yields.

Good LED grow lights are now considered the best lighting option by most growers due to their energy efficiency, durability and full spectrum. However, with all the options and technical jargon, finding the right light for your project can feel a little overwhelming.

Today, we’re going to answer a question we often get asked…

What Size LED Grow Light Do I Need?

To work out what size of LED grow light you need, you first need to calculate the exact size of your grow space.

The Size Of Your Grow Space

When growing cannabis, a good rule of thumb is to use a minimum of 50 watts of light per square foot of grow space. We want to flood our plants with light ( food ) so that they have lots of energy to produce big potent buds.

Therefore, we need to calculate the square footage ( length x width ) of our grow space. We’ll then multiply this number by 50w to give us the rough wattage of light we require.

EXAMPLE: I have a grow space that is 2ft long and 3ft wide. This gives me a square foot grow space of 6 ( 2ft x 3ft ). I then multiply this number by 50w, which gives me 300w. Therefore, in this example, I would require an LED grow light that was at least 300w.

How Many Plants Can I Grow?

In general, each cannabis plant you grow requires at least 1sq ft of space. After germination, I like to pot one plant in a large 5 gallon fabric container, which has a diameter of roughly 1 sq foot. My plant will stay in this pot until it flowers.

This allows the plant to grow big and strong without other plants or tent walls obstructing its progress. Using this as a guideline, I would be able to grow between 1-6 plants in my example above.

Most LED grow lights usually be able to cover about 1- 6 plants. If you want to grow any more plans than this, I’d purchase multiple lights to hang side by side ( called daisy chaining ) to cover the canopy and ensure each plant is getting enough light.

The table below shows how the power of grow light you require increases with the size of your grow space. I’ve also included how many plants each size of grow light will be adequate for.

Note: 1 sq ft grow space = 50 watts LED grow light

Grow Space Size Minimum Number of Watts Required Number of Plants You Can Grow
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*

* The size of the grow space in these situations will require you to purchase multiple lights to hang side by side to ensure the entire canopy is receiving light.

Note: The values above are for flowering. During the vegetation stage, you will require around half the power ( 25w ) Most good quality LED grow lights come with “Veg and Bloom switches” that optimise the lights intensity for the vegetation and flowering stages.

Understanding PAR Output

You’ve probably heard about PAR. In simple terms, It’s the part of the light spectrum that your plants use for photosynthesis. So It’s a pretty big deal. The higher the PAR output of your light, the more edible light your plants receive. Take a look at the table below for the optimal ranges of PAR for each stage of your plans life:

Stage Optimal PAR Output
Seedling 200-400 (μmol/m2/s)
Veg 400-600 (μmol/m2/s)
Flowering 600-900 (μmol/m2/s)

Ideally, you want to pick a grow light that outputs PAR in the ranges above. This pretty much rules out any LED grow light below 300w, as they simply don’t have enough power to generate the required levels of PAR. That said, keep in mind that these are optimal levels of PAR. Using a grow light that has less PAR output than these ranges will not be a disaster, you just won’t max out the potential of your plant.

So, Which LED Grow Light Should You Pick?

If you’re still unsure which LED grow light to go for, then I’ve written a detailed guide to the best LED grow lights which you might find helpful.

Alternatively, the three LED grow lights below are perfect for a small grow set up of between 1 – 4 plants inside a 1 sq ft –  4 sq ft grow space.

Top Pick
VIPARSPECTRA Reflector-Series 300W LED Grow Light Full Spectrum for Indoor Plants Veg and Flower
Roleadro LED Grow Light, Galaxyhydro Series 300W Indoor Plant Grow Lights Full Spectrum with UV&IR for Veg and Flower
MarsHydro LED Grow Light 300W 600W 1200W Full Spectrum for Hydroponic Indoor Plants Growing Veg and Flower
Name
Viparspectra
300w LED Grow Light
Roleadro
300w LED Grow Light
MarsHydro
300w LED Grow Light
Dimensions:
12.6 x 7.9 x 3 inches
12.1 x 8.2 x 2.4 inches
12 x 8 x 3 inches
Veg:
2ft x 2ft at 24"
2ft x 2ft at 24"
3ft x 2.5ft at 24"
Flowering
1.5ft x 1.5ft at 18"
-
2.5ft x 2ft at 18"
Power
Replaces a 250w HPS Consumes 136 watts
Replaces a 400w HPS Consumes 269 watts
Replaces a 300w HPS Consumes 132 watts
PAR Output
427 umols at 18"
453 umols at 18”
445 umols at 18”
Warranty
3 years
2.5 years
3 years
Daisy Chain Ability?
Veg & Bloom Switch?
Top Pick
VIPARSPECTRA Reflector-Series 300W LED Grow Light Full Spectrum for Indoor Plants Veg and Flower
Name
Viparspectra
300w LED Grow Light
Dimensions:
12.6 x 7.9 x 3 inches
Veg:
2ft x 2ft at 24"
Flowering
1.5ft x 1.5ft at 18"
Power
Replaces a 250w HPS Consumes 136 watts
PAR Output
427 umols at 18"
Warranty
3 years
Daisy Chain Ability?
Veg & Bloom Switch?
Roleadro LED Grow Light, Galaxyhydro Series 300W Indoor Plant Grow Lights Full Spectrum with UV&IR for Veg and Flower
Name
Roleadro
300w LED Grow Light
Dimensions:
12.1 x 8.2 x 2.4 inches
Veg:
2ft x 2ft at 24"
Flowering
-
Power
Replaces a 400w HPS Consumes 269 watts
PAR Output
453 umols at 18”
Warranty
2.5 years
Daisy Chain Ability?
Veg & Bloom Switch?
MarsHydro LED Grow Light 300W 600W 1200W Full Spectrum for Hydroponic Indoor Plants Growing Veg and Flower
Name
MarsHydro
300w LED Grow Light
Dimensions:
12 x 8 x 3 inches
Veg:
3ft x 2.5ft at 24"
Flowering
2.5ft x 2ft at 18"
Power
Replaces a 300w HPS Consumes 132 watts
PAR Output
445 umols at 18”
Warranty
3 years
Daisy Chain Ability?
Veg & Bloom Switch?

Final Thoughts

Hopefully this article has been able to shed some light ( pun intended ) on how to pick the correct size grow light for your project. As long as you know the size of your grow space and how many watts per square meter you need, choosing a an LED grow light is pretty simple.

If you have any questions at all about choosing a grow light, let us know in the comments below.

Good luck with your grow!

Last update on 2018-11-01 / Affiliate links / Images from Amazon Product Advertising API

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