Led grow light buyer`s guide – how to choose the best led grow light for your plants.

LED Grow Light buyer’s guide – how to choose the best Led Grow Light for your plants.

If you need help choosing an LED grow light or just want to learn about what led grow light specifications really matter, then you have come to the right place.

There is a lot of marketing around Led Grow Lights. But great marketing does not make a great LED Grow Light. Performance does. So, how do you choose the best LED light for your grow space?

Instead of telling you which LED to buy, I am going to offer you my knowledge and insight on how to choose an LED grow light for your grow. There are several factors to consider and these have been narrowed these down into six different considerations:

Light Intensity

Spectrum

Wattage Draw

Coverage Area

Warranty

Price

Let’s examine these factors more in-depth and determine why these factors are important when choosing an LED grow lights.

Light Intensity

Light intensity is one of the top considerations when choosing an LED grow light. You want the right amount of light intensity for the plant’s growth stage and for the size of your grow space. It is possible to have too much light on your plants however, most growers are concerned with the opposite—not having enough light.

When talking about light intensity, this is not how intense it appears to the human eye, but instead the quantityof photons that plants can use for growth and flowering.

So, how do you know which fixture will cover the area that you need it to cover with the correct amount of light intensity? Here’s how:

Use the recommended footprint from the manufacturer

This is the easiest and quickest way to know which light will be adequate for your grow space. Although, this doesn’t really tell you how much light is emitted from the fixture. Therefore, one manufacturer may claim that their light covers a 4’ x 4’ area, while another manufacturer that has a similar light with similar light intensity will say their light covers a 4.5’ x 4.5’ area.

Consider the PPF reading

Sometimes, coverage areas can be a little subjective. Therefore, use the PPF reading to determine how much light the fixture emits. PPF stands for Photosynthetic Photon Flux and is the total light output of the lamp in umol/s. This is measured in an integrating sphere. In general, if the PPF is above 1100 umol/s or so, it will cover a 4’ x 4’ area. About 1500 umol/s is the top of the range for a light that covers a 4’ x 4’ area.

PPF is an important measurement because it is an official measurement for light output and it creates a baseline for light output measurements across manufacturers. Yet, light intensity is not the entire story. When considering only light intensity, it is similar to saying that the sun emits ‘x’ number of photons. But what we actually care about is how much of that light hits the surface of the earth and how it is distributed across the surface? Similarly, we want to know how much of the light from the fixture strikes our plants and how is it distributed.

Consult the manufacturer’s PAR chart

Consulting the fixture’s PAR chart should be used in conjunction with considering the manufacturer’s recommended light footprint and PPF reading. A PAR chart, or Photosynthetic Active Radiation chart, is a map of the PPFD readings (or light intensity readings, in beginner speak) over the recommended footprint. PPFD stands for Photosynthetic Photon Flux Density.

The PAR map shows you how intense the light is over a given area and how that intensity is distributed. Every single light source is most intense in the middle of the fixture, less intense on the edges, and even lower in the corners.

Some LED Grow Lights emit all their light from a small surface area. Their PAR charts will be less uniform with higher numbers in the center and very low numbers in elsewhere over the map. Generally, these fixtures are placed higher above the plants.

Other fixtures have several lower power diodes over a large surface area. Their PAR charts will be more uniform. The highest numbers will still be highest in the center, but there will not be as big of a disparity between the center readings and edge or corner readings.

The average PPFD is one of the most important specs since this tells you the average light intensity over the given footprint. Sometimes, this spec is reported with or upon the PAR chart, but not always. The only downside to the average PPFD is that it doesn’t take uniformity into consideration.

Now, that you have these PPFD readings on a PAR map in front of you, you might be wondering what readings are typical for my stage of growth for an 18 hour veg period and a 12 hour flowering period?

Plants in the veg stage need around 300 PPFD to 600 PPFD. Some people veg at higher intensities. Plants in the flowering stage need at least 600 PPFD to 1000 PPFD. Higher intensities can be used when using CO2. These PPFD numbers vary since it depends on how hard you want to push your plants.

Some LED grow lights are dimmable which allow you to dial down the light intensity for seedlings and during veg to help save energy.

Spectrum

Spectrum is of second importance when choosing an LED grow light. You want to ensure you choose the correct spectrum for the stages of growth and development that your plants will go through. Some growers only need a light for veg, others for flowering, while most growers need a fixture to grow from seedling to flower.

There are two different types of spectrums on the market – targeted and broad.

A targeted spectrum uses specific wavelengths of diodes to match the photosynthetic peaks of chlorophyll absorption. Some brands will also target UVA, green, and Far Red. These ‘mono’, or narrowband wavelength, diodes were the first types of LEDs to hit the market and many brands still use this approach. The theory is that these wavelengths provide the optimal spectrum for plant growth. This approach is considered photosynthetically efficient.

The other type of spectrum is a broad, white-light spectrum. This approach uses white COBs or lower-powered white diodes, sometimes enhanced with other diodes (i.e. UV), to round out the spectrum. The idea here is that the white diode provides all or most of the essential wavelengths that the plants and for growth and flowering. This type of spectrum has more green light in it, contributed by the white diode, so the spectrum is more natural looking and the plant’s leaves appear normal, as opposed to pink or purple like a targeted spectrum approach would provide.

It is easy to say that the industry is moving toward a white light approach for a few reasons:

White light diodes are very efficient compared to narrowband wavelength diodes.

Plants look more natural under white light and therefore, it is easier to diagnose plant disease or pests.

The spectrum of a white light fixture contains a lot of green light and typically higher PFFD because of this. Medical plants are very light hungry and actually absorb much of the green light they are given, contrary to what most people think.

A fixture’s spectrum may be tunable or fixed. Fixed spectrums do not change. Fixtures that offer a tunable spectrum can be tuned either through veg and bloom on/off switches, by dimming down the respective veg or bloom channels, or remotely through a controller.

In general, increased blue light is better for veg since it keeps the distance between the internodes shorter which leads to squattier plants with less stretch. Increased red light is desired for the flowering stage since it helps drive yields. Having some red in the spectrum during veg is essential for healthy plants and having some blue in the spectrum for flower helps improve quality.

Light intensity and the ratio of red to blue light during flower will determine the yield. Relatively higher blue, say a 4000K white light spectrum or a 1:1 ratio of blue to red, will lead to smaller yields but of better quality. While relatively less blue, for example, a 3000K white light spectrum or about a 1:2 ratio of blue to red will result in higher yields but of slightly lower quality than a 4000K spectrum.

In sum, the best spectrum for your grow depends on the stage of growth your plants are in and what you want to get out of them—quality or yields.

Wattage Draw

Wattage draw has been used by growers for years to determine a fixture’s potential for growing. In general, a 400W HPS would flower a 2’ x 2’ area, a 600W HPS would flower a 3’ x 3’ area, and a 1000W HPS would flower a 4’ x 4’ area.

However, wattage does not exactly translate to light output (this is the number one mistake amateur growers make). The more efficient a fixture is the more light it will exude per watt. For instance, a light that is 2.5 umol/j that has a light output of 500W will have a PPF of 1250 umol/s. But a light that has an efficacy 2.0 umol/j and draws 600W (100W more watts than the previous example) will have a PPF of only 1,140 umol/s. In this example, more watts are used in the second case, but the light output is less. Point being, you can’t use wattage alone to determine the light output of a fixture. Wattage will only give you a general idea of how powerful a fixture might be, so take wattage with a grain of salt.

In 2018, we are seeing lights that only draw 480W and cover a 4’ x 4’ area. However, other companies will use fixtures that draw closer to 800W and cover slightly more than a 4’ x 4’ area. Why the large discrepancy? Some of this is due to efficiency. The higher wattage fixture will also have larger PPFD readings across the footprint.

You might consider a lower power fixture if energy consumption is of high importance to you. If you don’t care about energy consumption, but just want the best light for your money, then choose a light based off of other performance specs.

Wattage draw, efficacy and light output are more important to commercial growers since energy consumption really starts to add up, so they want the most amount of light for the least amount of wattage.

Also, be aware of fixtures that are titled ‘1000W’ or ‘600W’, for example. This usually refers to the diode wattage and not the actual power draw of the fixture. So, that proclaimed 1000W fixture you found on Amazon or Ebay may actually only draw 250W.

Many growers want to know how many watts you need per square foot for flowering. This number varies, but sits around 32 watts per square foot. Sometimes less (down to 30W), but sometimes more (up to 40W). There is not a single answer, because everyone flowers at different intensities with fixtures of different efficacies.

As an aside, ensure that the light is rated for your particular voltage application. Most home growers in the USA use 120V, but some may use 240V. Commercial grows may use 240V or higher. Most LED grow lights these days have a flexible driver and are rated for 110-277VAC.

The takeaway here is to use wattage as a guide and to determine how much power the fixture will draw from your wall. Instead of using wattage to choose an LED grow light, use the PPFD readings on the PAR map, uniformity, and total light output in umol/s, as discussed above.