How to choose an LED grow light

Factors to consider when choosing an LED grow light

There are a lot of things to consider when setting up a new grow area or simply choosing and LED grow light for your existing grow space including:

  • What size grow area do I need?
  • How many plants to grow in your grow tent or grow area?
  • How much yield will I get from my grow space?
  • What grow light wattage you need for your space?
  • What is the best grow light spectrum?
  • How much should I pay for an high quality grow light?
  • What grow light features to look for?

What size grow area do I need?

You may have identified a space in your house or shed to put a grow tent or have a cupboard or small room you want to convert for growing. Most growers will use a grow tent and a good place to start is looking at the most popular grow tent sizes and the approximate number of plants you can grow.

How many plants can you fit in your grow space

The more plants you put into a grow area the less each plant has to grow to fill the canopy and utilise all of the light energy available. Growing a larger number of smaller plants also gives you some safety in numbers should some plants die. However the downside is requiring more seeds, pots etc. Larger plants require much longer to veg so the time to harvest will also be longer. 

Autoflower plants tend to grow faster and can be relatively smaller than photoperiod plants with a long vegging time.

The yield you can get from your grow space

There is a wide range of yield possible from a grow space and it can depend on many aspects such as:

  • Plant genetics
  • Growing medium
  • Grow light wattage
  • Environment control
  • Growers experience

However, we have spoken to a lot of new and experienced growers to determine the general range of yield potential. We have produced a guide for expected yield by grow area, grow light wattage and by plant in the below chart

The first point to note is that Photoperiod plants take a lot longer to grow to harvest at initial 18/6 light cycle and then 12/12. Autoflower plants can be grown in a 20/4 light cycle, receive more light each day and mature to harvest sooner.

The range of yield per plant depends on the genetics and final size of the plant. Photoperiod plants vegged for a long time will be at the upper range and smaller photoperiod plants and autoflowers will be at the lower end of the range.

The yield per watt of grow light depends most on the growing medium. In general Hydro is most efficient, coco next and soil least efficient (this also has many variables but is generally true, all other things being equal). It also depends on the efficiency of the grow light but most current LED grow light are similar efficiency, within about a 10% range.

The yield for a given grow area is a good general guide to estimating your required grow space for a target yield but also depends on the above factors as to where in that range your grow will perform.

Grow light wattage for your grow space

To maximise the yield from your grow space it is necessary to deliver a high average PAR to the plant canopy. However there is a reducing rate of return as you increase the average PAR above a certain level. We recommend an average PAR of about 800µmols/m²/second for photoperiod plants. Above this level you may need elevated CO2 which allows the plants to absorb higher PAR intensity.

To achieve 800µmols/m²/second in your grow space with modern, high efficiency, LED grow light you need the following grow light wattage for your space.

Autoflowers have a longer light cycle and the optimum PAR level is lower to deliver the same total PAR per day required to maximise the potential growth rate.

The best Grow Light spectrum

Using LEDs allows us to tailor the grow light spectrum that we want to deliver to the plants. However you may notice that most grow light manufacturers use a very similar LED selection to achieve the best full spectrum output to grow from seed to harvest. This is generally achieved by using a mix of cool and warm white LEDs and 660nm deep reds.

The mixture of white LEDs delivers a neutral white of about 4000K CT which has about 12% to 15% blue. Blue is critical for short internodal distances (distance between branches) and above 5% will deliver the desired short and dense growth.

The 660nm reds are very efficient in terms of electrical efficiency (PAR output per watt) and also photosynthetically efficient. They are relatively expensive but add a 'turbo charge' to the overall system efficiency of the grow light in terms of PAR output per watt.

This grow light spectrum is perfect to grow healthy plants. There are arguments that adding Far Red to promote flowering and UVA to stimulate higher potency but none of these theories are proven. In our view if you want to maximise yield and potency delivering high intensity PAR levels to your plant canopy is the best way to achieve this goal.

In summary there is little difference between most grow light spectrum on the market and for good reason, the established standard spectrum is close to optimal for growing plants from seed to harvest.

Features to look for in a grow light

The form of LED grow lights has changed over the years. The first LED grow lights were 'Blurple' LED grow lights with just blue and red LEDs and in boxes with fans in them.

These were replaced with COB grow lights with larger, high powered LEDs with lenses but are no longer manufactured due to higher cost of production and limited efficiency.

Panel LED grow lights or 'quantum boards' are still available, particularly suitable for smaller grow areas as they are very cheap to produce.

However most LED grow lights produced are now in LED bar format as they deliver light to the edges of the plant canopy, are cheap to produce and have a high system efficiency.

One of the most important pieces of information to look for a grow light it is a PAR map or PAR chart for the grow light in it's specified grow area. This is a graphical illustration of the PAR intensity the fixture delivers at the recommended hanging height and area.

It is critical to see the PAR intensity and spread across the plant canopy. It is important to see how uniform and intense the PAR is and be able to compare to other light fixtures you are considering.

Most of the larger fixtures will have dimming capability built in and the option of using an external controller and daisy chain multiple fixtures in larger grow rooms.

Some other features to look for are:

Can the LED driver be hung outside the grow room to reduce heat in the grow room?

Are the LEDs protected from dirt and moisture with acrylic or silicone coating?

Is the warranty at least three years and what are the terms i.e. is delivery, parts and labour included?

How much a high quality grow light costs

There is still a wide range of prices you can pay for a grow light for a given grow area. However as an example we list below a range of grow lights for a 5ft x 5ft or 1.5m x 1.5m area. You can see that generally the more you pay for a light the efficiency is higher and it will pay you back over time as the electricity running costs are lower.

Not your size? try here:

12 best grow lights for a 2 x 2 grow space (0.6m x 0.6m)

7 best grow lights for a 3 x 3 grow space (1m x 1m)

10 best grow lights for a 4 x 2 grow space (1.2m x .6m)

16 best grow lights for a 4 x 4 grow space (1.2m x 1.2m)

21 best grow lights for a 5 x 5 grow space (1.5m x 1.5m)

The bets value LED grow light for a 5x5 space

Grow light quality and service delivery

New grow lights are being released all the time so it is difficult to know the long term reliability of most models on the market. However you can research the brand and model on forums and review sites. Customer of the brand will give you some indication of the companies reliability and service levels so you can avoid companies with bad reputations. There are many good grow light manufacturers you can chose from.

Best of luck with your choice and happy growing

 

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