How to choose the best LED grow lights

How to choose the best LED grow light to grow weed

The best LED grow lights: an introduction

Choosing an LED grow light is really tough. There are so many options to choose from. So, how do you choose the best LED grow lights for you? We would like to share with you some of our experience and expertise in LED lighting and help you choose the best LED grow light for growing weed.

Product names in this industry can be misleading. One trend we have spotted in the LED grow light industry is what companies are naming their products. For instance, one company may call their products the GrowLight720w, which implies it pulls 720 Watts. In fact, it may only pull 200 Watts. This means that the light output will be much lower than you anticipate. This can cause havoc when growing weed as you are going to need a lot of output power to grow your marijuana plants when they start to get bigger.

How to choose the best LED Grow Light: Understanding wattage

There are a couple of things that you need to know about how to choose the best LED grow light.

Understanding LED grow light watts

There are LED light manufacturers that state that their LED grow lights are 5 Watt LEDs or a 3 Watt LED. Just because they call it that, doesn’t actually mean it is. There are plenty of 5 Watt LEDs that may only be pulling 2 Watts of power and they look to be about 3 Watts but overdriven (which is not great for the LED itself and will lead to premature failure). Some LED grow light manufacturers will put 100 of these 5 watt lights together and call it a 500 Watt bulb when in reality, it’s pulling 200 Watts from the wall so you have a 200 Watt light being marketed as a 500 Watt light. This is totally misleading and will not provide the power you need for growing weed. Many beginners are caught out with this and get frustrated when their marijuana doesn’t grow as expected.

You need to disregard what the manufacturers are telling you the LED grow lights are, and instead look at what they are actually pulling from the mains.

Understanding watts per foot

The important thing to understand when growing weed indoors is watts per foot. In any commercial horticulture grow area (which will include your indoor grow area), when you’re using grow lights, you’re going to have a watt per foot ratio that you’re looking for.

With commercial HID (High-intensity discharge lamps) it’s always been a benchmark of 50 watts per foot. That’s industry standard in the horticulture world. With LED grow lights, you’re looking usually at a lower number. We recommend about 30 watts to 35 watts per foot for LED grow lights.

Most people who grow weed indoors just buy a lamp, find a space to grow and go for it. However, you need to remember that you will lose approximately half of your marijuana plants halfway through your project (by removing all male plants). You will still need to grow all these plants to a certain point (till when you can determine the sex) so you need to ensure that there is enough power. In fact, more power is better than less power. The female plants will use up this excess power in their flowering stage anyway.

The experienced home growers will understand this and first measure their growing area, work out the watts per foot required, and then look at a suitable LED grow light.

Let’s say we have a 3ft x 3ft space, and we are aiming for 30+ watts per foot. That’s 270 watts required. Let’s round it up to 300 watts. First, you’re going to be looking for a 300+ watt LED grow light for this growing area. That gives us something to work towards.

It’s worth mentioning about primary and secondary optics at this point and how it affects your LED grow light output.

How to choose the best LED Grow Light: Primary and secondary optics

How to choose the best LED grow light - effective light

You want all your light to fall on plant

Many LED lights use both a primary and secondary optic (including LED Grow lights).

The primary optic is built into the LED itself, and usually takes the form of a small dome on top of the device. This is designed to maximise the useful light output of the LED and provides the basic beam shape of the light output.

Secondary optics, such as lenses or reflectors, are then used to shape the light. Sometime the light will be spread out and other times the light will be more focused. This is then measured in lens angle with a lower number being a more focused beam.

Secondary optics are also required for blending colours for output light. For example, if you are blending the blue/red lightwaves lengths crucial for growing weed.

There’s a myth in the marijuana growing community that secondary optics reduce the light output. This is both true and false. It’s true because any kind of material put over an LED reduces the total light output. But the difference is, if you take a secondary optic like a lens that is specifically built for that LED, it actually has a compound effect. It can actually increase the efficiency of your grow lights.

How to choose the best LED grow light - non-effective light

Be aware of wasted light

So, if you’re covering a 3ft x 3ftspace, and let’s say you had no secondary optic. It’s just the bare LED with no secondary optics to narrow the beam. Any light that ‘overshoots’ that 3ft x 3ft area is lost. Even with reflective walls, the distance traveled by the light makes it much less powerful. It’s essentially wasted light that your marijuana plant could have used.

The key to maximising light when you are growing weed, is to get the light from your LED grow light straight to the plant canopy in the shortest distance possible.

Any light that does not hit the canopy of the marijuana plants directly is wasted light. Now, by adding a secondary optic, you can focus that light much better to the grow area you want. Just like turning a nozzle to a hosepipe from spray to narrow, you can focus your light much more in the shortest distance possible.

How to choose the best LED grow light - reflected light

The reflected light is not as effective

Let’s say your LED grow lights have a total output level of 100 units. When you add a secondary optic that may well reduce to 90 units but the actual light that your marijuana plants will receive for photosynthesis is massively increased.

The light which can be used by plants for photosynthesis is measured in PARS (photosynthetically active radiation). By adding a secondary optic, and focusing the light output, you may increase the PAR from 400 to 600 plus. We’ve only lost 10 Watts of output power by adding a secondary optic, but we’ve massively increased the PAR that is used by the marijuana plants to actually grow. That is what really counts and that is why its important to get your LED grow light angles correct.

What angle of secondary optics is best?

How to choose the best LED grow light - non-effective set-up

Wide optics have too much wasted light

We would recommend a secondary optic of approx 90 degrees. We would not recommend an LED grow light with a 60 degree or less. Some companies will take a 1 Watt LED and they’ll put a 45-degree optic on it which makes the light really focused. The problem is that the light is too focused. What you end up with is light being driven through a 45 or a 60 degree LED grow light with a core coverage that’s so tight and small that you’re not actually efficiently covering the entire growing area. You need your light to evenly cover as much as the marijuana plant canopy as possible, in the shortest distance possible. Imagine having a large flowerbed and the sunlight only hits a small area of that flowerbed. What will happen? Only the plants in that small area of light will thrive. The rest will simply not grow or even worse, die.

How to choose the best LED grow light - effective set-up

90 degree angles provide a better coverage

We have found that LED grow lights with a 90 degree angle is perfect. At 90 degrees, if you’re grow lights are two feet away from the plant, then you’re getting a four-foot coverage. If your lights are one feet away, then you get a two foot coverage. The distance is double for the coverage with a 90-degree optic. So it’s a perfect situation.

We would always recommend a secondary optic so you can get as much light coverage to the plant canopy as possible.

How to choose the best LED Grow Light: Understanding PAR

PAR per watt is a really important metric that is often abused in LED grow light marketing. Photosynthetically active radiation (PAR) is the light waves of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.

A lot of companies will give you the PAR but it is misleading. They will give you the central PAR which is misleading.

If you take any given light source, and you measure straight directly down underneath it, this is the centre PAR. It is easy for a manufacturer to create a high central PAR but what is important is the average PAR coverage. Not just one small, central point. It is easy to create an LED grow light with a 45 degree secondary optic have a really high PAR but in reality, that light will be pretty ineffective at growing weed because the overall PAR coverage would be low.

What you need to look for is the total PAR per watt and the overall coverage of that PAR.

A better way to measure PAR is to take a PAR reading in centre of each quadrant of grow area for a total and then divide it by the running watts. That then gives a much more accurate and useful reading.

We see this all the time with cheap, imported LED grow lights. They state over-inflated watts and PAR readings. It’s all very misleading and nearly always ends with disappointing end results.

How to choose the best LED Grow Light: getting the right colour

Choosing an LED grow light with the right lightwave output is critical. If you get a light which emits a load of infrared or greens and yellows, then that is wasted energy (for growing weed anyway).

The colour spectrum output of your LED grow lights is absolutely critical. The colours you need are dependant upon the plants you are growing. If you have a vegetative cycle (like marijuana in it’s early stages) you want mostly blue spectrum light. You still want other colours included, but blue is the most important colour at this stage.

If you’re using heavy flowering or fruiting plants (like marijuana in it’s later stages), you want a lot of red light. Again, your oranges are important but mainly red is required at this stage.

When growing weed, you need to look for an LED grow light that outputs mainly blue and red light.

How to choose the best LED Grow Light: getting maximum PAR

PAR is just simply a measurement of radiation from 400 to 700 nanometers. What we are looking for is high PAR within the key colours of the spectrum for that plant. For example, we do not care much about green and yellow light or the PAR in that light wave (marijuana leaves are green as that light is reflected). Marijuana plants will absorb green, but just not as efficiently.

The colours we are looking for when growing weed are blue and the red lights. So, we want to look for the maximum amount of PAR per watt and PAR inside of that range. That is what is really important and what will help the marijuana plants grow and produce a maximum crop.

How to choose the best LED Grow Light: Buy cheap, buy twice

Buying a cheap LED grow light is a massive false economy. Often the components used in cheap, imported LED grow lights are sub-standard or are running so hard they fail. It’s essential that your LED grow lights produce as many PAR per watt as possible, especially within the key blue and red light wave lengths. This requires not only knowledge of growing weed and what marijuana requires but also about how LED lights work in terms of even coverage to provide your plant canopy with enough quality light to grow and flourish.

There is nothing worse than investing time and money into growing weed, having to discard all your male plants halfway through and then having your lights not produce enough PAR (or even worse fail) during the flowering stage and lose all your crops. It’s not only heartbreaking but also a massive loss of a valuable crop.

Always look to buy LED grow lights that have been manufactured to a high quality by a company who is more interested in producing quality LED grow lights as opposed to churning out loads of LED lights for financial return.

In our experience, if you buy cheap, you not only buy twice but you also lose a lot of crop in the process.

So, now you know how to choose the best LED grow light for you, get started!

Good luck with your growing project – stay happy.

2 Comments on "How to choose the best LED grow lights"

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  2. Great writing!

    Do you have any article about LED vs HPS?

    I think LED is good but it needs a huge initial investment for the commercial grower. So it will helpful if you publish a comparison table between LED & HPS light.

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